ILLUSTRATED DICTIONARY OF

ELECTRICAL &
ELECTRONICS ENGINEERING
3RD EDITION
Edited by:

Antonio Escobar-Molero
• TERMS • DEFINITIONS • EXAMPLES
DESIGNED FOR SENIOR HIGH TO
UNDERGRADUATE STUDENTS

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ILLUSTRATED DICTIONARY OF ELECTRICAL & ELECTRONICS ENGINEERING
3RD EDITION

Edited by: Antonio Escobar-Molero

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Electrical &
Electronics
Engineering
“Electronics are getting more and more accessible now - you
don’t have to be an engineer to start building things.”
― Simone Giertz

From powering up the Global Positioning System to generating electric power, the field of electrical
engineering has been a driving force behind an extensive array of technological advancements. These
engineers are the architects behind the design, development, testing, and supervision of electrical
systems and electronic devices. They operate at the forefront of practical technology, enhancing
the devices and systems that permeate our daily lives, spanning from solar-energy systems to the
ubiquitous mobile phones. Their innovations address society’s communication, technological, and
energy needs. To deal with the subjects of electrical and electronics engineering, a fundamental
grasp of the associated terms is paramount. Familiarity with the basic terminology in this domain
facilitates a profound understanding of the subject matter. The 3rd edition of the Illustrated
Dictionary of Electrical & Electronics Engineering stands as a comprehensive resource, equipped
with updated terms and revised content. The dictionary employs descriptive illustrations that
offer a concise and thorough comprehension of the subject. It presents state-of-the-art scientific
and practical terms in an easily navigable A-Z order, complemented by visuals and examples to
elucidate each term. The user-friendly layout, with guide words at the top of each page and an
A-Z ‘tab’ index, ensures accessibility. Vibrant, colorful illustrations and photographs make the
learning experience enjoyable, while full sentence definitions and examples place the headwords
in familiar contexts.

Aa
15 kV AC
The 15 kV, 16.7 Hz AC railway
electrification system is used in
Germany, Austria, Switzerland, Sweden
and Norway. The high voltage enables
high power transmission with the lower
frequency reducing the losses of the
traction motors that were available
at the beginning of the 20th century.
Railway electrification in late 20th
century tends to use 25 kV, 50 Hz AC
systems which has become the preferred
standard for new railway electrifications
but extensions of the existing 15 kV

networks are not completely unlikely.
In particular, the Gotthard Base Tunnel
(opened on 1 June 2016) still uses 15
kV, 16.7 Hz electrification. Due to high
conversion costs, it is unlikely that
existing 15 kV, 16.7 Hz systems will be
converted to 25 kV, 50 Hz despite the
fact that this would reduce the weight
of the on-board step-down transformers
to one third that of the present devices.

ILLUSTRATED DICTIONARY OF ELECTRICAL & ELECTRONICS ENGINEERING

A

2D computer graphics

30 seconds before applying the plate
voltage.

2D computer graphics is the computerbased generation of digital images—
mostly from two-dimensional models
(such as 2D geometric models, text,
and digital images) and by techniques
specific to them. The word may stand
for the branch of computer science
that comprises such techniques, or for
the models themselves. 2D computer
graphics are mainly used in applications
that were originally developed upon
traditional printing and drawing
technologies, such as typography,
cartography, technical drawing,
advertising, etc. In those applications,
the two-dimensional image is not just
a representation of a real-world object,
but an independent artifact with added
semantic value; two-dimensional models
are therefore preferred, because they
give more direct control of the image
than 3D computer graphics (whose
approach is more akin to photography
than to typography).

A (amp)
The ampere often shortened to amp,
is the unit of electric current in the
International System of Units (SI).
One ampere is equal to 1 coulomb
moving past a point in 1 second, or
6.241509074×1018 electrons’ worth of
charge moving past a point in 1 second.

866A

AAC

The 866 is a mercury vapor half-wave
rectifier intended for high-voltage
applications. The voltage drop is
approximately 15 volts up to 150 Hz.
To avoid unwanted shorts the tube
must be operated in a vertical position
and the filament preheated for at least

AAC is short for Augmentative
and Alternative Communication.
Communication devices, systems,
strategies and tools that replace or
support natural speech are known
as augmentative and alternative
communication (AAC). These tools
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support a person who has difficulties
communicating using speech.

distortion depending on the type
A
of aberration.

Abrasion (mechanical)
Abrasion is the process of scuffing,
scratching, wearing down, marring, or
rubbing away. It can be intentionally
imposed in a controlled process using an
abrasive. Abrasion can be an undesirable
effect of exposure to normal use or
exposure to the elements.

ABC
The American Broadcasting Company is
an American multinational commercial
broadcast television network that is
a flagship property of Walt Disney
Television, a division of Disney General
Entertainment Content of The Walt
Disney Company.

ABS
An anti-lock braking system is a safety
anti-skid braking system used on
aircraft and on land vehicles, such as
cars, motorcycles, trucks, and buses.

Aberration
Aberration is a property of optical
systems such as lenses that causes
light to be spread out over some
region of space rather than focused
to a point. Aberrations cause the
image formed by a lens to be blurred
or distorted, with the nature of the

Absolute error
Absolute Error is the amount of error in
your measurements. It is the difference
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A

between the measured value and “true”
value. For example, if a scale states
90 pounds but you know your true
weight is 89 pounds, then the scale has
an absolute error of 90 lbs – 89 lbs =
1 lbs.

Absorption coefficient
The absorption coefficient determines
how far into a material light of a
particular wavelength can penetrate
before it is absorbed. In a material with
a low absorption coefficient, light is only
poorly absorbed, and if the material is
thin enough, it will appear transparent
to that wavelength. The absorption
coefficient depends on the material and
also on the wavelength of light which
is being absorbed.

Absolute zero
Absolute zero is the lowest limit of
the thermodynamic temperature scale,
a state at which the enthalpy and
entropy of a cooled ideal gas reach their
minimum value, taken as zero kelvins.

Absorption

Absorption loss

The process of absorption means that
a substance captures and transforms
energy. The absorbent distributes
the material it captures throughout
whole and adsorbent only distributes
it through the surface. The process of
gas or liquid which penetrate into the
body of adsorbent is commonly known
as absorption.

That part of the transmission loss caused
by the dissipation or conversion of
electrical, electromagnetic, or acoustic
energy into other forms of energy as a
result of its interaction with a material
medium.

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that, averaged over a complete cycle
A
of the AC waveform, results in net
transfer of energy in one direction is
known as active power (more commonly
called real power to avoid ambiguity
especially in discussions of loads with
non-sinusoidal currents). The portion
of power due to stored energy, which
returns to the source in each cycle, is
known as reactive power.

AC adapter
An AC adapter, AC/DC adapter, or AC/
DC converter is a type of external power
supply, often enclosed in a case similar
to an AC plug. Other common names
include plug pack, plug-in adapter,
adapter block, domestic mains adapter,
line power adapter, wall wart, power
brick, and power adapter. Adapters for
battery-powered equipment may be
described as chargers or rechargers (see
also battery charger). AC adapters are
used with electrical devices that require
power but do not contain internal
components to derive the required
voltage and power from mains power.
The internal circuitry of an external
power supply is very similar to the
design that would be used for a builtin or internal supply.

AC power plugs and
sockets
AC power plugs and sockets are
devices that allow electrically operated
equipment to be connected to the
primary alternating current (AC) power
supply in a building. Electrical plugs
and sockets differ in voltage and
current rating, shape, size and type
of connectors. The types used in each
country are set by national standards,
some of which are listed in the IEC
technical report TR 60083, Plugs and
socket-outlets for domestic and similar
general use standardized in member
countries of IEC. The scope of IEC TR
60083 states: “The report only contains
systems for which standard sheets have
been published in a National Standard,
which may be a National Standard of

AC power
Power in an electric circuit is the rate
of flow of energy past a given point
of the circuit. In alternating current
circuits, energy storage elements such
as inductors and capacitors may result
in periodic reversals of the direction
of energy flow. The portion of power
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A

the country itself or any other IEC
member country”.

AC/DC receiver design
AC/AC converter

An AC/DC receiver design is a style of
power supply of vacuum tube radio or
television receivers that eliminated the
bulky and expensive mains transformer.
A side-effect of the design was that the
receiver could in principle operate from
a DC supply as well as an AC supply.
Consequently, they were known as “AC/
DC receivers”.

A solid-state AC-AC converter converts
an AC waveform to another AC
waveform, where the output voltage
and frequency can be set arbitrarily.

AC/DC conversion
A rectifier is an electrical device that
converts alternating current (AC),
which periodically reverses direction,
to direct current (DC), which flows
in only one direction. The process
is known as rectification, since it
“straightens” the direction of current.
Physically, rectifiers take a number of
forms, including vacuum tube diodes,
mercury-arc valves, stacks of copper and
selenium oxide plates, semiconductor
diodes, silicon-controlled rectifiers
and other silicon-based semiconductor
switches. Historically, even synchronous
electromechanical switches and motors
have been used. Early radio receivers,
called crystal radios, used a “cat’s
whisker” of fine wire pressing on a
crystal of galena (lead sulfide) to serve
as a point-contact rectifier or “crystal
detector”.

Accelerated life test
Accelerated life testing is the process
of testing a product by subjecting it to
conditions (stress, strain, temperatures,
voltage, vibration rate, pressure etc.) in
excess of its normal service parameters
in an effort to uncover faults and
potential modes of failure in a short
amount of time.

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by converting the signal’s energy into
A
mechanical motion. An actuator is the
mechanism by which a control system
acts upon an environment. The control
system can be simple (a fixed mechanical
or electronic system), software-based
(e.g. a printer driver, robot control
system), a human, or any other input.

Accelerating anode
An electrode in an electron tube to
which, typically, a positive potential
is applied to increase the velocity of
cathode rays.

Active rectification
Active rectification, or synchronous
rectification, is a technique for
improving the efficiency of rectification
by replacing diodes with actively
controlled switches such as transistors,
usually power MOSFETs or power BJTs.
Historically, vibrator driven switches or
motor-driven commutators have also
been used for mechanical rectifiers and
synchronous rectification.

Adaptive control
Adaptive control is the control method
used by a controller which must adapt
to a controlled system with parameters
which vary, or are initially uncertain.
For example, as an aircraft flies, its
mass will slowly decrease as a result
of fuel consumption; a control law
is needed that adapts itself to such
changing conditions. Adaptive control
is different from robust control in that
it does not need a priori information
about the bounds on these uncertain or
time-varying parameters; robust control
guarantees that if the changes are within
given bounds the control law need not
be changed, while adaptive control is
concerned with control law changing
itself.

Actuator
An actuator is a component of a machine
that is responsible for moving and
controlling a mechanism or system, for
example by opening a valve. In simple
terms, it is a “mover”. An actuator
requires a control signal and a source
of energy. The control signal is relatively
low energy and may be electric voltage
or current, pneumatic or hydraulic
pressure, or even human power. Its
main energy source may be an electric
current, hydraulic fluid pressure, or
pneumatic pressure. When it receives
a control signal, an actuator responds
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ILLUSTRATED DICTIONARY OF ELECTRICAL & ELECTRONICS ENGINEERING

Affinity law

A

The affinity laws (Also known as the
“Fan Laws” or “Pump Laws”) for
pumps/fans are used in hydraulics,
hydronics and/or HVAC to express the
relationship between variables involved
in pump or fan performance (such as
head, volumetric flow rate, shaft speed)
and power. They apply to pumps, fans,
and hydraulic turbines. In these rotary
implements, the affinity laws apply both
to centrifugal and axial flows. The laws
are derived using the Buckingham π
theorem. The affinity laws are useful
as they allow prediction of the head
discharge characteristic of a pump or fan
from a known characteristic measured at
a different speed or impeller diameter.
The only requirement is that the two
pumps or fans are dynamically similar,
that is the ratios of the fluid forced are
the same.

Adjustable-speed drive
Adjustable speed drive (ASD) or
variable-speed drive (VSD) describes
equipment used to control the speed of
machinery. Many industrial processes
such as assembly lines must operate at
different speeds for different products.
Where process conditions demand
adjustment of flow from a pump or fan,
varying the speed of the drive may save
energy compared with other techniques
for flow control. Where speeds may be
selected from several different pre-set
ranges, usually the drive is said to be
adjustable speed. If the output speed
can be changed without steps over a
range, the drive is usually referred to as
variable speed. Adjustable and variable
speed drives may be purely mechanical,
electromechanical, hydraulic, or
electronic.

AIEE
The American Institute of Electrical
Engineers (AIEE) was a United States
based organization of electrical engineers
that existed from 1884 through 1962.
On January 1, 1963 it merged with
the Institute of Radio Engineers (IRE)
to form the Institute of Electrical and
Electronics Engineers (IEEE).

Alloy
An alloy is a mixture of metals or a
mixture of a metal and another element.
Alloys are defined by a metallic bonding
character. An alloy may be a solid
solution of metal elements (a single
phase) or a mixture of metallic phases
(two or more solutions). Intermetallic
compounds are alloys with a defined

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stoichiometry and crystal structure. Zintl
phases are also sometimes considered
alloys depending on bond types (see
also: Van Arkel-Ketelaar triangle for
information on classifying bonding in
binary compounds). Alloys are used in
a wide variety of applications. In some
cases, a combination of metals may
reduce the overall cost of the material
while preserving important properties.
In other cases, the combination of
metals imparts synergistic properties
to the constituent metal elements such
as corrosion resistance or mechanical
strength. Examples of alloys are steel,
solder, brass, pewter, duralumin, bronze
and amalgams.

quickly after it was featured on the cover
A
of the January 1975 issue (published
in late November 1974) of Popular
Electronics, and was sold by mail
order through advertisements there, in
Radio-Electronics, and in other hobbyist
magazines. The designers hoped to
sell a few hundred build-it-yourself
kits to hobbyists, and were surprised
when they sold thousands in the first
month. The Altair also appealed to
individuals and businesses that just
wanted a computer and purchased the
assembled version. The Altair is widely
recognized as the spark that ignited
the microcomputer revolution as the
first commercially successful personal
computer. The computer bus designed
for the Altair was to become a de facto
standard in the form of the S-100 bus,
and the first programming language for
the machine was Microsoft’s founding
product, Altair BASIC.

Alpha–beta transformation
In electrical engineering, the alphabeta ( αβγ ) transformation (also known
as the Clarke transformation) is a
mathematical transformation employed
to simplify the analysis of three-phase
circuits. Conceptually it is similar to the
dq0 transformation. One very useful
application of the αβγ transformation
is the generation of the reference signal
used for space vector modulation control
of three-phase inverters.

Alternating current
Alternating current (AC) is an electric
current which periodically reverses
direction, in contrast to direct current
(DC) which flows only in one direction.
Alternating current is the form in
which electric power is delivered to
businesses and residences, and it is the

Altair 8800
The Altair 8800 is a microcomputer
designed in 1974 by MITS and based
on the Intel 8080 CPU. Interest grew
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A

form of electrical energy that consumers
typically use when they plug kitchen
appliances, televisions, fans and electric
lamps into a wall socket. A common
source of DC power is a battery cell
in a flashlight. The abbreviations AC
and DC are often used to mean simply
alternating and direct, as when they
modify current or voltage.

Alternator synchronization
In an alternating current electric power
system, synchronization is the process of
matching the speed and frequency of a
generator or other source to a running
network. An AC generator cannot
deliver power to an electrical grid unless
it is running at the same frequency as
the network. If two segments of a grid
are disconnected, they cannot exchange
AC power again until they are brought
back into exact synchronization. A direct
current (DC) generator can be connected
to a power network by adjusting its
open-circuit terminal voltage to match
the network voltage, by either adjusting
its speed or its field excitation. The exact
engine speed is not critical. However,
an AC generator must match both
the amplitude and the timing of the
network voltage, which requires both
speed and excitation to be systematically
controlled for synchronization. This extra
complexity was one of the arguments
against AC operation during the War of
Currents in the 1880s. In modern grids,
synchronization of generators is carried
out by automatic systems.

Alternator
An alternator is an electrical generator
that converts mechanical energy
to electrical energy in the form of
alternating current. For reasons of
cost and simplicity, most alternators
use a rotating magnetic field with a
stationary armature. Occasionally, a
linear alternator or a rotating armature
with a stationary magnetic field is
used. In principle, any AC electrical
generator can be called an alternator,
but usually the term refers to small
rotating machines driven by automotive
and other internal combustion engines.
An alternator that uses a permanent
magnet for its magnetic field is called a
magneto. Alternators in power stations
driven by steam turbines are called
turbo-alternators. Large 50 or 60 Hz
three phase alternators in power plants
generate most of the world’s electric
power, which is distributed by electric
power grids.

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significant amounts of greenhouse gas
A
emissions.

American wire gauge

Altitude
Altitude or height (sometimes known
as depth) is defined based on the
context in which it is used (aviation,
geometry, geographical survey, sport,
atmospheric pressure, and many more).
As a general definition, altitude is a
distance measurement, usually in the
vertical or “up” direction, between a
reference datum and a point or object.
The reference datum also often varies
according to the context. Although the
term altitude is commonly used to mean
the height above sea level of a location,
in geography the term elevation is often
preferred for this usage.

Aluminium smelting
Aluminium smelting is the process of
extracting aluminium from its oxide,
alumina, generally by the Hall-Héroult
process. Alumina is extracted from the
ore bauxite by means of the Bayer
process at an alumina refinery. This is
an electrolytic process, so an aluminium
smelter uses prodigious amounts of
electricity; they tend to be located very
close to large power stations, often
hydro-electric ones, and near ports
since almost all of them use imported
alumina. A large amount of carbon is
also used in this process, resulting in

American Wire Gauge (AWG) is the
standard way to denote wire size in
North America. In AWG, the larger the
number, the smaller the wire diameter
and thickness. The largest standard
size is 0000 AWG, and 40 AWG is the
smallest standard size. It may also be
called Brown & Sharpe wire gauge or
simply the gauge of the wire.

Ammeter
An ammeter (from Ampere Meter) is a
measuring instrument used to measure
the current in a circuit. Electric currents
are measured in amperes (A), hence
the name. Instruments used to measure
smaller currents, in the milliampere or
microampere range, are designated as
milliammeters or microammeters. Early
ammeters were laboratory instruments
which relied on the Earth’s magnetic
field for operation. By the late 19th
century, improved instruments were
designed which could be mounted
in any position and allowed accurate
measurements in electric power systems.
It is generally represented by letter ‘A’
in a circle.
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ILLUSTRATED DICTIONARY OF ELECTRICAL & ELECTRONICS ENGINEERING

countries. Ampacity is defined as the
maximum amount of electric current
a conductor or device can carry before
sustaining immediate or progressive
deterioration. Also described as current
rating or current-carrying capacity,
ampacity is the RMS electric current
which a device or conductor can
continuously carry while remaining
within its temperature rating.

A

Amorphous metal
transformer

Ampere hour

An amorphous metal transformer (AMT)
is a type of energy efficient transformer
found on electric grids. The magnetic
core of this transformer is made with
a ferromagnetic amorphous metal. The
typical material (Metglas) is an alloy of
iron with boron, silicon, and phosphorus
in the form of thin (e.g. 25 µm) foils.
These materials have high magnetic
susceptibility, very low coercivity and
high electrical resistance. The high
resistance and thin foils lead to low
losses by eddy currents when subjected
to alternating magnetic fields. On the
downside amorphous alloys have a
lower saturation induction and often
a higher magnetostriction compared
to conventional crystalline iron-silicon
electrical steel.

An ampere-hour or amp-hour is a unit
of electric charge, having dimensions
of electric current multiplied by time,
equal to the charge transferred by a
steady current of one ampere flowing
for one hour, or 3,600 coulombs. The
commonly seen milliampere-hour is
one-thousandth of an ampere-hour.

Ampère’s circuital law
In classical electromagnetism, Ampère’s
circuital law (not to be confused with
Ampère’s force law that André-Marie
Ampère discovered in 1823) relates
the integrated magnetic field around
a closed loop to the electric current

Ampacity
Ampacity is a portmanteau for ampere
capacity defined by National Electrical
Safety Codes, in some North American
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passing through the loop. James Clerk
Maxwell (not Ampère) derived it using
hydrodynamics in his 1861 paper “On
Physical Lines of Force” and it is now one
of the Maxwell equations, which form
the basis of classical electromagnetism.

Ampère’s force law
In magnetostatics, the force of attraction
or repulsion between two currentcarrying wires (see first figure below)
is often called Ampère’s force law. The
physical origin of this force is that
each wire generates a magnetic field,
following the Biot–Savart law, and the
other wire experiences a magnetic force
as a consequence, following the Lorentz
force law.

Amplifier
An amplifier, electronic amplifier or
(informally) amp is an electronic device
that can increase the power of a signal
(a time-varying voltage or current). An
amplifier uses electric power from a
power supply to increase the amplitude
of a signal. The amount of amplification
provided by an amplifier is measured
by its gain: the ratio of output voltage,
current, or power to input. An amplifier
is a circuit that has a power gain greater
than one.

Amplidyne
An amplidyne is an electromechanical
amplifier invented prior to World War II
by Ernst Alexanderson. It consists of an
electric motor driving a DC generator.
The signal to be amplified is applied to
the generator’s field winding, and its
output voltage is an amplified copy of
the field current. The amplidyne is used
in industry in high power servo and
control systems, to amplify low power
control signals to control powerful
electric motors, for example. It is now
mostly obsolete.

Amplitude modulation
Amplitude modulation (AM) is a
modulation technique used in electronic
communication, most commonly for
transmitting information via a radio
carrier wave. In amplitude modulation,
the amplitude (signal strength) of the
carrier wave is varied in proportion to
the waveform being transmitted. That
waveform may, for instance, correspond
to the sounds to be reproduced by a
loudspeaker, or the light intensity
of television pixels. This technique
contrasts with frequency modulation,
in which the frequency of the carrier
signal is varied, and phase modulation,
in which its phase is varied.

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A

Analog circuit

pointer on the scale to indicate the
level of measurement being made. The
pointer deflects from its initial position
increasingly as the measuring quantity
increases.

Analogue electronics (also spelled
analog electronics) are electronic
systems with a continuously variable
signal, in contrast to digital electronics
where signals usually take only two
levels. The term “analogue” describes
the proportional relationship between
a signal and a voltage or current that
represents the signal.

Analog filter
Analogue filters are a basic building
block of signal processing much used
in electronics. Amongst their many
applications are the separation of an
audio signal before application to bass,
mid-range and tweeter loudspeakers;
the combining and later separation of
multiple telephone conversations onto a
single channel; the selection of a chosen
radio station in a radio receiver and
rejection of others.

Analog signal
An analog signal is any continuous
signal for which the time varying feature
(variable) of the signal is a representation
of some other time varying quantity, i.e.,
analogous to another time varying signal.
For example, in an analog audio signal,
the instantaneous voltage of the signal
varies continuously with the pressure of
the sound waves. It differs from a digital
signal, in which the continuous quantity
is a representation of a sequence of
discrete values which can only take
on one of a finite number of values.
The term analog signal usually refers to
electrical signals; however, mechanical,
pneumatic, hydraulic, human speech,
and other systems may also convey or
be considered analog signals. An analog
signal uses some property of the medium
to convey the signal’s information. For

Analog Multimeter
An analog multimeter is a permanent
magnet moving coil (PMMC) meter type
measuring instrument. It works on the
principle of d’Arsonval galvanometer.
The analog multimeter has an analog
display that uses the deflection of a
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example, an aneroid barometer uses
rotary position as the signal to convey
pressure information. In an electrical
signal, the voltage, current, or frequency
of the signal may be varied to represent
the information.

Analog-to-digital converter
In electronics, an analog-to-digital
converter (ADC, A/D, or A-to-D) is
a system that converts an analog
signal, such as a sound picked up
by a microphone or light entering a
digital camera, into a digital signal.
An ADC may also provide an isolated
measurement such as an electronic
device that converts an input analog
voltage or current to a digital number
representing the magnitude of the
voltage or current. Typically the digital
output is a two’s complement binary
number that is proportional to the input,
but there are other possibilities.

Analog signal processing
Analog signal processing is any type
of signal processing conducted on
continuous analog signals by some
analog means (as opposed to the discrete
Digital Signal Processing where the signal
processing is carried out by a digital
process). “Analog” indicates something
that is mathematically represented as
a set of continuous values. This differs
from “digital” which uses a series of
discrete quantities to represent signal.
Analog values are typically represented
as a voltage, electric current, or electric
charge around components in the
electronic devices. An error or noise
affecting such physical quantities will
result in a corresponding error in the
signals represented by such physical
quantities. Examples of analog signal
processing include crossover filters
in loudspeakers, “bass”, “treble” and
“volume” controls on stereos, and
“tint” controls on TVs. Common analog
processing elements include capacitors,
resistors, inductors and transistors.

Annealing (metallurgy)
Annealing, in metallurgy and materials
science, is a heat treatment that alters
the physical and sometimes chemical
properties of a material to increase its
ductility and reduce its hardness, making
it more workable. It involves heating
a material above its recrystallization
temperature, maintaining a suitable
temperature, and then cooling. In
annealing, atoms migrate in the crystal
lattice and the number of dislocations
decreases, leading to a change in ductility
and hardness. As the material cools it
recrystallizes. For many alloys, including
carbon steel, the crystal grain size and
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moving in metal conductors, used with a
transmitter or receiver. In transmission,
a radio transmitter supplies an electric
current to the antenna’s terminals,
and the antenna radiates the energy
from the current as electromagnetic
waves (radio waves). In reception, an
antenna intercepts some of the power
of an electromagnetic wave in order
to produce an electric current at its
terminals that is applied to a receiver
to be amplified. Antennas are essential
components of all radio equipment,
and are used in radio broadcasting,
broadcast television, two-way radio,
communications receivers, radar, cell
phones, satellite communications and
other devices.

phase composition, which ultimately
determine the material properties, are
dependent on the heating, and cooling
rate. Hot working or cold working after
the annealing process alter the metal
structure, so further heat treatments
may be used to achieve the properties
required. With knowledge of the
composition and phase diagram, heat
treatment can be used to adjust between
harder and more brittle, to softer and
more ductile.

Anode
An anode is an electrode through
which conventional current flows into
a polarized electrical device. A common
mnemonic is ACID for “anode current
into device”. The direction of (positive)
electric current is opposite to the
direction of electron flow: (negatively
charged) electrons flow out the anode
to the outside circuit. An anode is also
the wire or plate having excess positive
charge. Consequently, anions will tend
to move towards the anode.

Antilog
The anti-logarithm of a number is the
inverse process of finding the logarithms
of the same number. If x is the logarithm
of a number y with a given base b,
then y is the anti-logarithm of (antilog)
of x to the base b. Natural Logarithms
and Anti-Logarithms have their base
as 2.7183.

Antenna (radio)
In radio, an antenna is the interface
between radio waves propagating
through space and electric currents
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Apc
Automatic phase control. A device that
protects from over voltage and also does
quality control.

it is the product of rms voltage and rms
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current. The unit for reactive power is
expressed as var, which stands for voltampere reactive. Since reactive power
transfers no net energy to the load, it
is sometimes called “wattless” power.

Arc converter

Apollo program
The Apollo program, also known as
Project Apollo, was the third United
States human spaceflight program
carried out by the National Aeronautics
and Space Administration (NASA),
which accomplished landing the first
humans on the Moon from 1969 to
1972. First conceived during Dwight D.
Eisenhower’s administration as a threeman spacecraft to follow the one-man
Project Mercury which put the first
Americans in space, Apollo was later
dedicated to President John F. Kennedy’s
national goal of “landing a man on the
Moon and returning him safely to the
Earth” by the end of the 1960s, which
he proposed in an address to Congress
on May 25, 1961.

Apparent power
Apparent power is conventionally
expressed in volt-amperes (VA) since

The arc converter, sometimes called
the arc transmitter, or Poulsen arc after
Danish engineer Valdemar Poulsen
who invented it in 1903, was a variety
of spark transmitter used in early
wireless telegraphy. The arc converter
used an electric arc to convert direct
current electricity into radio frequency
alternating current. It was used as
a radio transmitter from 1903 until
the 1920s when it was replaced by
vacuum tube transmitters. One of the
first transmitters that could generate
continuous sinusoidal waves, it was one
of the first technologies used to transmit
sound (amplitude modulation) by radio.
It is on the list of IEEE Milestones as
a historic achievement in electrical
engineering.

Arc furnace
An Electric Arc Furnace (EAF) is a
furnace that heats charged material by
means of an electric arc. Industrial arc
furnaces range in size from small units
of approximately one ton capacity (used
in foundries for producing cast iron
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products) up to about 400 ton units used
for secondary steelmaking. Arc furnaces
used in research laboratories and by
dentists may have a capacity of only a
few dozen grams. Industrial electric arc
furnace temperatures can be up to 1,800
°C (3,272 °F), while laboratory units can
exceed 3,000 °C (5,432 °F). Arc furnaces
differ from induction furnaces in that
the charge material is directly exposed
to an electric arc and the current in the
furnace terminals passes through the
charged material.

Arc welder
Arc welding is a process that is used to
join metal to metal by using electricity
to create enough heat to melt metal,
and the melted metals when cool result
in a binding of the metals. It is a type
of welding that uses a welding power
supply to create an electric arc between
an electrode and the base material to melt
the metals at the welding point. They
can use either direct (DC) or alternating
(AC) current, and consumable or nonconsumable electrodes. The welding
region is usually protected by some
type of shielding gas, vapor, or slag.
Arc welding processes may be manual,
semi-automatic, or fully automated.
First developed in the late part of
the 19th century, arc welding became
commercially important in shipbuilding
during the Second World War. Today
it remains an important process for
the fabrication of steel structures and
vehicles.

Arc lamp
An arc lamp or arc light is a lamp that
produces light by an electric arc (also
called a voltaic arc). The carbon arc
light, which consists of an arc between
carbon electrodes in air, invented by
Humphry Davy in the first decade of
the 1800s, was the first practical electric
light. It was widely used starting in
the 1870s for street and large building
lighting until it was superseded by
the incandescent light in the early
20th century. It continued in use in
more specialized applications where a
high intensity point light source was
needed, such as searchlights and movie
projectors until after World War II. The
carbon arc lamp is now obsolete for all
of these purposes and is only still made
for very specialized purposes where a
high intensity UV source is needed.
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Argon
Argon is a chemical element with
symbol Ar and atomic number 18. It
is in group 18 of the periodic table and
is a noble gas. Argon is the third-most
abundant gas in the Earth’s atmosphere,
at 0.934% (9340 ppmv). It is more than
twice as abundant as water vapor
(which averages about 4000 ppmv, but
varies greatly), 23 times as abundant as
carbon dioxide (400 ppmv), and more
than 500 times as abundant as neon (18
ppmv). Argon is the most abundant
noble gas in Earth’s crust, comprising
0.00015% of the crust. Nearly all of
the argon in the Earth’s atmosphere is
radiogenic argon-40, derived from the
decay of potassium-40 in the Earth’s
crust. In the universe, argon-36 is by
far the most common argon isotope, as
it is the most easily produced by stellar
nucleosynthesis in supernovas.

comprise either permanent magnets, or
A
electromagnets formed by a conducting
coil, such as another armature (i.e.,
doubly-fed electric machine). The
armature, in contrast, must carry
current, so it is always a conductor or
a conductive coil, oriented normal to
both the field and to the direction of
motion, torque (rotating machine), or
force (linear machine). The armature’s
role is twofold. The first is to carry
current crossing the field, thus creating
shaft torque in a rotating machine or
force in a linear machine. The second
role is to generate an electromotive force
(EMF). In the armature, an electromotive
force is created by the relative motion
of the armature and the field. When the
machine is used as a motor, this EMF
opposes the armature current, and the
armature converts electrical power to
mechanical power in the form of torque,
and transfers it via the shaft. When
the machine is used as a generator,
the armature EMF drives the armature
current, and the shaft’s movement is
converted to electrical power. In an
induction generator, generated power
is drawn from the stator.

Armature (electrical
engineering)
In electrical engineering, an armature
is the power-producing component of
an electric machine. The armature can
be on either the rotor (rotating part)
or the stator (stationary part) of the
electric machine. The armature interacts
with the magnetic field (magnetic flux)
in the air-gap; the field component can

Artificial heart
An artificial heart is a device that
replaces the heart. Artificial hearts are
typically used to bridge the time to
heart transplantation, or to permanently
replace the heart in case heart
transplantation is impossible. Although
other similar inventions preceded it from
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transfer protocols. This type of circuit
is contrasted with synchronous circuits,
in which changes to the signal values
in the circuit are triggered by repetitive
pulses called a clock signal. Most digital
devices today use synchronous circuits.
However asynchronous circuits have
the potential to be faster, and may
also have advantages in lower power
consumption, lower electromagnetic
interference, and better modularity in
large systems. Asynchronous circuits
are an active area of research in digital
logic design.

the late 1940s, the first artificial heart to
be successfully implanted in a human
was the Jarvik-7 in 1982, designed by a
team including Willem Johan Kolff and
Robert Jarvik.

Audio and video connector
Audio connectors and video connectors
are electrical connectors (or optical
connectors) - plugs and sockets for carrying audio signal and video
signal. Audio interfaces and video
interfaces define physical parameters
and interpretation of signals. For digital
audio and digital video, this can be
thought of as defining the physical
layer, data link layer, and most or all
of the application layer. For analog
audio and analog video these functions
are all represented in a single signal
specification like NTSC or the direct
speaker-driving signal of analog audio.
Physical characteristics of the electrical
or optical equipment includes the types
and numbers of wires required, voltages,
frequencies, optical intensity, and the
physical design of the connectors.
Any data link layer details define how
application data is encapsulated (for
example for synchronization or errorcorrection). Application layer details
define the actual audio or video format
being transmitted, often incorporating
a codecs not specific to the interface,
such as PCM, MPEG-2, or the DTS
Coherent Acoustics codec. In some

Artificial intelligence
Artificial intelligence (AI, also machine
intelligence, MI) is intelligence
demonstrated by machines, in contrast
to the natural intelligence (NI) displayed
by humans and other animals. In
computer science AI research is defined
as the study of “intelligent agents”: any
device that perceives its environment
and takes actions that maximize its
chance of successfully achieving its
goals. Colloquially, the term “artificial
intelligence” is applied when a machine
mimics “cognitive” functions that
humans associate with other human
minds, such as “learning” and “problem
solving”.

Asynchronous circuit
An asynchronous circuit, or self-timed
circuit, is a sequential digital logic
circuit which is not governed by a
clock circuit or global clock signal.
Instead it often uses signals that
indicate completion of instructions and
operations, specified by simple data
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cases, the application layer is left open;
for example, HDMI contains an Ethernet
channel for general data transmission.

Audio equipment
Audio equipment refers to devices that
reproduce, record, or process sound.
This includes microphones, radio
receivers, AV receivers, CD players, tape
recorders, amplifiers, mixing consoles,
effects units, and loudspeakers.

Audio filter
An audio filter is a frequency dependent
amplifier circuit, working in the audio
frequency range, 0 Hz to beyond 20
kHz. Audio filters can amplify (“boost”),
pass or attenuate (“cut”) some frequency
ranges. Many types of filters exist for
different audio applications including hifi stereo systems, musical synthesizers,
sound effects, sound reinforcement
systems, instrument amplifiers and
virtual reality systems.

unit of audio frequency is the hertz (Hz).
A
It is the property of sound that most
determines pitch. The generally accepted
standard range of audible frequencies is
20 to 20,000 Hz, although the range of
frequencies individuals hear is greatly
influenced by environmental factors.
Frequencies below 20 Hz are generally
felt rather than heard, assuming the
amplitude of the vibration is great
enough. Frequencies above 20,000 Hz
can sometimes be sensed by young
people. High frequencies are the first
to be affected by hearing loss due to
age and/or prolonged exposure to very
loud noises.

Audio signal processing
Audio signal processing or audio
processing is the intentional alteration
of audio signals often through an audio
effect or effects unit. As audio signals
may be electronically represented in
either digital or analog format, signal
processing may occur in either domain.
Analog processors operate directly
on the electrical signal, while digital
processors operate mathematically on
the digital representation of that signal.

Audion tube

Audio frequency
An audio frequency (abbreviation: AF)
or audible frequency is characterized as
a periodic vibration whose frequency is
audible to the average human. The SI

The Audion was an electronic amplifying
vacuum tube invented by American
electrical engineer Lee de Forest in 1906.
It was the first triode, consisting of a
partially evacuated glass tube containing
three electrodes; a heated filament, a
grid, and a plate. It is important in the
history of technology because it was
the first widely used electrical device
which could amplify a small electrical
signal applied to the grid could control a
larger current flowing from the filament
to plate.
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Automatic Flow Controller

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Used in controlling the flow of gasses
under pressure into a vacuum system.

Automatic frequency
control
Automatic Frequency Control (AFC) is
a technique used in communication
systems to ensure that the carrier
frequency of a transmitted signal
remains at a constant and accurate
frequency. AFC is commonly used in
many communication systems, including
AM and FM radio broadcasting,
television broadcasting, and wireless
communication systems such as WiFi and Bluetooth. It is an essential
technique for maintaining accurate
and stable communication signals
over long distances and in challenging
environments.

Austin transformer
An Austin transformer is a special type
of an Isolation transformer used for
feeding the air-traffic obstacle lamps and
other devices on a mast radiator antenna
insulated from ground. As the electrical
potential difference between the antenna
and ground is high (up to 300 kV),
feeding the lamps directly is impossible.
The transformer consists of two ringlike windings with a large air space
between the winding and the magnetic
core. The large spacing provides both
isolation from high voltage and low
inter-winding coupling capacitance.

Automatic gain control
Automatic gain control (AGC), also
called automatic volume control (AVC),
is a closed-loop feedback regulating
circuit, the purpose of which is to
provide a controlled signal amplitude
at its output, despite variation of the
amplitude in the input signal. The
average or peak output signal level is
used to dynamically adjust the input-tooutput gain to a suitable value, enabling
the circuit to work satisfactorily with

Automatic Fine Tuning
An electronic circuit used to
automatically keep a resonant
circuit tuned to the frequency of an
incoming radio signal.

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a greater range of input signal levels.
It is used in most radio receivers to
equalize the average volume (loudness)
of different radio stations due to
differences in received signal strength,
as well as variations in a single station’s
radio signal due to fading. Without AGC
the sound emitted from an AM radio
receiver would vary to an extreme extent
from a weak to a strong signal; the AGC
effectively reduces the volume if the
signal is strong and raises it when it is
weaker. AGC is derived from detector
and given to RF and IF stages.

Automatic transfer switch
A transfer switch is an electrical switch
that switches a load between two
sources. Some transfer switches are
manual, in that an operator effects the
transfer by throwing a switch, while
others are automatic and trigger when
they sense one of the sources has lost
or gained power. An Automatic Transfer
Switch (ATS) is often installed where
a backup generator is located, so that
the generator may provide temporary
electrical power if the utility source fails.

A

Automatic Volume Control
An automatic volume control (AVC)
automatically adjusts the volume, or
loudness, of an audio signal, usually
to compensate for ambient noise in an
effort to make the audio signal better
heard and understood above the noise.
An AVC is primarily used to enhance
intelligibility of speech or appreciation
of music heard by the user in noisy
environments. Most conventional AVCs
attempt to keep the signal-to-noise ratio
(S/N) constant for the user.

Automation
Automation can be defined as the
technology by which a process or
procedure is performed without
human assistance. In other words,
Automation or automatic control, is
the use of various control systems for
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Autotransformer

operating equipment such as machinery,
processes in factories, boilers and heat
treating ovens, switching on telephone
networks, steering and stabilization of
ships, aircraft and other applications
and vehicles with minimal or reduced
human intervention. Some processes
have been completely automated.

An autotransformer (sometimes called
autostep down transformer) is an
electrical transformer with only one
winding. The “auto” (Greek for “self”)
prefix refers to the single coil acting
alone and not to any kind of automatic
mechanism. In an autotransformer,
portions of the same winding act
as both the primary and secondary
sides of the transformer. In contrast,
an ordinary transformer has separate
primary and secondary windings which
are not electrically connected. The
winding has at least three taps where
electrical connections are made. Since
part of the winding does “double duty”,
autotransformers have the advantages of
often being smaller, lighter, and cheaper
than typical dual-winding transformers,
but the disadvantage of not providing
electrical isolation between primary and
secondary circuits. Other advantages of
autotransformers include lower leakage
reactance, lower losses, lower excitation
current, and increased VA rating for a
given size and mass.

Autorecloser
In electric power distribution, a
recloser, or autorecloser, is a circuit
breaker equipped with a mechanism
that can automatically close the breaker
after it has been opened due to a
fault. Reclosers are used on overhead
distribution systems to detect and
interrupt momentary faults. Since many
short-circuits on overhead lines clear
themselves, a recloser improves service
continuity by automatically restoring
power to the line after a momentary
fault.

Autotransformers are often used to
step up or step down voltages in the
110-115-120 V range and voltages in
the 220-230-240 V range - for example,
providing 110 V or 120 V (with taps)
from 230 V input, allowing equipment
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designed for 100 or 120 V to be used
with a 230 V supply. This allows US
electrical equipment to be fed from the
higher voltages used in Europe and
elsewhere. Autotransformers can also
be used to supply 230 V appliances
from a 100 to 120 V supply within the
US. In all cases the supply and the
autotransformer must be correctly rated
to supply the required power.

Availability factor
The availability factor of a power plant
is the amount of time that it is able
to produce electricity over a certain
period, divided by the amount of the
time in the period. Occasions where
only partial capacity is available may or
may not be deducted. Where they are
deducted, the metric is titled equivalent
availability factor (EAF). The availability
factor should not be confused with the
capacity factor. The capacity factor for
a given period can never exceed the
availability factor for the same period.
The difference arises when the plant is
run at less than full capacity, in which
case the capacity factor is less than the
availability factor.

Avalanche diode
In electronics, an avalanche diode is
a diode (made from silicon or other

semiconductor) that is designed to
A
experience avalanche breakdown
at a specified reverse bias voltage.
The junction of an avalanche diode
is designed to prevent current
concentration and resulting hot spots,
so that the diode is undamaged by the
breakdown. The avalanche breakdown
is due to minority carriers accelerated
enough to create ionization in the
crystal lattice, producing more carriers
which in turn create more ionization.
Because the avalanche breakdown is
uniform across the whole junction, the
breakdown voltage is nearly constant
with changing current when compared
to a non-avalanche diode.

Average rectified value
In electrical engineering, the average
rectified value (ARV) of the quantity is
the average of its absolute value. The
average of a symmetric alternating value
is zero and it is therefore not useful to
characterize it. Thus the easiest way to
determine a quantitative measurement
size is to use the average rectified
value. The average rectified value is
mainly used to characterize alternating
voltage and alternating current. It can
be computed by averaging the absolute
value of a waveform over one full period
of the waveform.

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B

Bb
B-H curve
The B-H curve is the curve characteristic
of the magnetic properties of a material
or element or alloy.

Babinet’s principle
Babinet’s principle states that the
diffraction pattern from an opaque
body is identical to that from a hole
of the same size and shape except for
the overall forward beam intensity. It
was formulated in the 1800s by French
physicist Jacques Babinet.

Balanced line
In telecommunications and professional
audio, a balanced line or balanced signal
pair is a transmission line consisting of
two conductors of the same type, each
of which have equal impedances along
their lengths and equal impedances to
ground and to other circuits. The chief
advantage of the balanced line format
is good rejection of external noise when
fed to a differential amplifier. Common
forms of balanced line are twin-lead,
used for radio frequency signals and
twisted pair, used for lower frequencies.
They are to be contrasted to unbalanced
lines, such as coaxial cable, which is
designed to have its return conductor
connected to ground, or circuits whose
return conductor actually is ground.
Balanced and unbalanced circuits can
be interconnected using a transformer
called a balun.

Backward wave oscillator
A backward wave oscillator (BWO), also
called carcinotron (a trade name for
tubes manufactured by CSF, now Thales)
or backward wave tube, is a vacuum
tube that is used to generate microwaves
up to the terahertz range. It belongs to
the traveling-wave tube family. It is an
oscillator with a wide electronic tuning
range. An electron gun generates an
electron beam that is interacting with
a slow-wave structure. It sustains the
oscillations by propagating a traveling
wave backwards against the beam.
The generated electromagnetic wave
power has its group velocity directed
oppositely to the direction of motion
of the electrons. The output power is
coupled out near the electron gun.

Ball bearing motor
A ball bearing motor is an unusual
electric motor that consists of two ballbearing-type bearings, with the inner
races mounted on a common conductive
shaft, and the outer races connected to a
high current, low voltage power supply.
An alternative construction fits the outer
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races inside a metal tube, while the inner
races are mounted on a shaft with a
non-conductive section (e.g. two sleeves
on an insulating rod). This method has
the advantage that the tube will act as
a flywheel. The direction of rotation is
determined by the initial spin which is
usually required to get it going.

Band-pass filter

Balun

Band-stop filter

A balun is an electrical device that
converts between a balanced signal (two
signals working against each other where
ground is irrelevant) and an unbalanced
signal (a single signal working against
ground or pseudo-ground). A balun
can take many forms and may include
devices that also transform impedances
but need not do so. Transformer baluns
can also be used to connect lines of
differing impedance. Sometimes, in the
case of transformer baluns, they use
magnetic coupling but need not do so.
Common-mode chokes are also used as
baluns and work by eliminating, rather
than ignoring, common mode signals.

In signal processing, a band-stop filter
or band-rejection filter is a filter that
passes most frequencies unaltered, but
attenuates those in a specific range to
very low levels. It is the opposite of
a band-pass filter. A notch filter is a
band-stop filter with a narrow stop band
(high Q factor).

A band-pass filter (also band pass filter, B
BPF) is a device that passes frequencies
within a certain range and rejects
(attenuates) frequencies outside that
range.

Bandwidth (signal
processing)
Bandwidth is the difference between
the upper and lower frequencies in
a continuous set of frequencies. It
is typically measured in hertz, and
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B

may sometimes refer to pass band
bandwidth, sometimes to baseband
bandwidth, depending on context.
Pass band bandwidth is the difference
between the upper and lower cutoff
frequencies of, for example, a bandpass filter, a communication channel,
or a signal spectrum. In the case of a
low-pass filter or baseband signal, the
bandwidth is equal to its upper cutoff
frequency. Bandwidth in hertz is a
central concept in many fields, including
electronics, information theory, digital
communications, radio communications,
signal processing, and spectroscopy and
is one of the determinants of the capacity
of a given communication channel.

bang controllers are variable structure
systems, and bang–bang controllers are
thus variable structure controllers.

Barlow’s wheel
Barlow’s wheel was an early
demonstration of a homopolar
motor, designed and built by English
mathematician and physicist, Peter
Barlow in 1822. An electric current
passes through the hub of the wheel
to a mercury contact on the rim; this
is contained in a small trough through
which the rim passes. Due to health and
safety considerations brine is sometimes
used today in place of mercury. The
interaction of the current with the
magnetic field of a U-magnet causes
the wheel to rotate. The presence of
serrations on the wheel is unnecessary
and the apparatus will work with a
round metal disk, usually made of
copper.

Bang-bang control
A bang–bang controller (2 step or on–off
controller), also known as a hysteresis
controller, is a feedback controller that
switches abruptly between two states.
These controllers may be realized in
terms of any element that provides
hysteresis. They are often used to control
a plant that accepts a binary input,
for example a furnace that is either
completely on or completely off. Most
common residential thermostats are
bang–bang controllers. The Heaviside
step function in its discrete form is
an example of a bang–bang control
signal. Due to the discontinuous control
signal, systems that include bang–
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Bartlett’s bisection
theorem
Bartlett’s Bisection Theorem is an
electrical theorem in network analysis
attributed to Albert Charles Bartlett. The
theorem shows that any symmetrical
two-port network can be transformed
into a lattice network. The theorem
often appears in filter theory where
the lattice network is sometimes
known as a filter X-section following
the common filter theory practice of
naming sections after alphabetic letters
to which they bear a resemblance. The
theorem as originally stated by Bartlett
required the two halves of the network
to be topologically symmetrical. The
theorem was later extended by Wilhelm
Cauer to apply to all networks which
were electrically symmetrical. That is,
the physical implementation of the
network is not of any relevance. It is
only required that its response in both
halves are symmetrical.

Base load power plant
The base load on a grid is the minimum
level of demand on an electrical grid
over a span of time, for example, one
week. Base load power sources are
power stations which can economically
generate the electrical power needed to
satisfy this minimum demand. Because
they have a relatively high annual
contribution to the energy supply, they
are designed with features to minimize
fuel cost. Daily peaks in grid load are
met with generating plants that may
have higher fuel costs, but which operate
for only a part of a day.

B

Battery (electricity)
An electric battery is a device consisting
of one or more electrochemical cells with
external connections provided to power
electrical devices such as flashlights,
smartphones, and electric cars. When
a battery is supplying electric power,
its positive terminal is the cathode and
its negative terminal is the anode. The
terminal marked negative is the source
of electrons that when connected to an
external circuit will flow and deliver
energy to an external device. When
a battery is connected to an external
circuit, electrolytes are able to move
as ions within, allowing the chemical
reactions to be completed at the separate
terminals and so deliver energy to the
external circuit. It is the movement of
those ions within the battery which
allows current to flow out of the battery
to perform work. Historically the term
“battery” specifically referred to a device
composed of multiple cells, however
the usage has evolved additionally to
include devices composed of a single
cell.

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B

Battery eliminator
A battery eliminator is a device powered
by an electrical source other than a
battery, which then converts the source
to a suitable DC voltage that may be
used by a second device designed to
be powered by batteries. A battery
eliminator eliminates the need to replace
batteries but may remove the advantage
of portability. A battery eliminator is
also effective in replacing obsolete
battery designs. Some examples of
battery eliminators include the nine volt
mains power supply, the size and shape
of a PP9 battery, originally intended to
replace the battery in portable radios
in the 1960s. A solar panel providing
power for a portable appliance may
also be considered a battery eliminator.
The term is also sometimes used as a
misnomer when using a bigger battery
for more runtime when branching out
a power supply to wired electrical
equipment using DC input.

Bayer filter
A Bayer filter mosaic is a color filter
array (CFA) for arranging RGB color
filters on a square grid of photosensors.
Its particular arrangement of color filters
is used in most single-chip digital
image sensors used in digital cameras,
camcorders, and scanners to create a
color image. The filter pattern is 50%
green, 25% red and 25% blue, hence
is also called BGGR, RGBG, GRGB, or
RGGB.

Baud

Beam tetrode

In telecommunication and electronics,
baud is a common unit of measurement
of symbol rate, which is one of the
components that determine the speed
of communication over a data channel. It
is the unit for symbol rate or modulation
rate in symbols per second or pulses
per second.

A beam tetrode, sometimes called
a “beam power tube”, is a type of
tetrode vacuum tube (or ‘valve’) with
auxiliary beam-focusing plates designed
to augment power-handling capability
and help reduce unwanted emission
effects. These tubes are usually used
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for power amplification, especially at
audio-frequency.

Beat frequency oscillator
A beat frequency oscillator or BFO is a B
dedicated oscillator used to create an
audio frequency signal from Morse code
radiotelegraphy (CW) transmissions to
make them audible.

Beat frequency
In acoustics, a beat is an interference
pattern between two sounds of slightly
different frequencies, perceived as a
periodic variation in volume whose rate
is the difference of the two frequencies.
When tuning instruments that can
produce sustained tones, beats can be
readily recognized. Tuning two tones to
a unison will present a peculiar effect:
when the two tones are close in pitch but
not identical, the difference in frequency
generates the beating. The volume
varies like in a tremolo as the sounds
alternately interfere constructively and
destructively. As the two tones gradually
approach unison, the beating slows
down and may become as slow as to
be imperceptible.

Biasing (electronics)
Biasing in electronics means establishing
predetermined voltages or currents at
various points of an electronic circuit
for the purpose of establishing proper
operating conditions in electronic
components. Many electronic devices
such as transistors and vacuum tubes,
whose function is processing timevarying (AC) signals also require a
steady (DC) current or voltage to
operate correctly — a bias. The AC
signal applied to them is superposed
on this DC bias current or voltage.
The operating point of a device, also
known as bias point, quiescent point, or
Q-point, is the steady-state (DC) voltage
or current at a specified terminal of an
active device (a transistor or vacuum
tube) with no input signal applied. A
bias circuit is a portion of the device’s
circuit which supplies this steady
current or voltage.

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B

BIBO stability

Binary coded decimal

In signal processing, specifically control
theory, bounded-input, bounded-output
(BIBO) stability is a form of stability
for linear signals and systems that take
inputs. If a system is BIBO stable, then
the output will be bounded for every
input to the system that is bounded.

Binary-coded decimal is a system of
writing numerals that assigns a fourdigit binary code to each digit 0 through
9 in a decimal (base 10) number. Simply
put, binary-coded decimal is a way to
convert decimal numbers into their
binary equivalents.

Bilinear transform

Biot–Savart law

The bilinear transform (also known as
Tustin’s method) is used in digital signal
processing and discrete-time control
theory to transform continuous-time
system representations to discrete-time
and vice versa.

The Biot–Savart law is an equation
describing the magnetic field generated
by a stationary electric current. It relates
the magnetic field to the magnitude,
direction, length, and proximity of the
electric current. The Biot–Savart law is
fundamental to magnetostatics, playing
a similar role to Coulomb’s law in
electrostatics. When magnetostatics does
not apply, the Biot–Savart law should
be replaced by Jefimenko’s equations.
The law is valid in the magnetostatic
approximation, and is consistent with
both Ampère’s circuital law and Gauss’s
law for magnetism. It is named after
Jean-Baptiste Biot and Félix Savart who
discovered this relationship in 1820.

Bimetallic strip
A bimetallic strip is used to convert
a temperature change into mechanical
displacement. The strip consists of two
strips of different metals which expand
at different rates as they are heated,
usually steel and copper, or in some
cases steel and brass. The strips are
joined together throughout their length
by riveting, brazing or welding. The
different expansions force the flat strip
to bend one way if heated, and in the
opposite direction if cooled below its
initial temperature. The metal with the
higher coefficient of thermal expansion
is on the outer side of the curve when
the strip is heated and on the inner side
when cooled.

Bipolar junction transistor
A bipolar junction transistor (bipolar
transistor or BJT) is a type of transistor
that uses both electron and hole charge
carriers. In contrast, unipolar transistors,
such as field-effect transistors, only
use one kind of charge carrier. For
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their operation, BJTs use two junctions
between two semiconductor types, n-type
and p-type. BJTs are manufactured in
two types, NPN and PNP, and are
available as individual components, or
fabricated in integrated circuits, often
in large numbers. The basic function
of a BJT is to amplify current. This
allows BJTs to be used as amplifiers or
switches, giving them wide applicability
in electronic equipment, including
computers, televisions, mobile phones,
audio amplifiers, industrial control, and
radio transmitters.

can be varied as desired. However, a
blocked rotor current test is conducted
on squirrel cage rotor motors.
B

Blu-ray Disc
Blu-ray or Blu-ray Disc (BD) is a digital
optical disc data storage format. It was
designed to supersede the DVD format,
in that it is capable of storing hours of
video in high-definition (HDTV 720p
and 1080p) and ultra-high-definition
resolution (2160p). The main application
of Blu-ray is as a medium for video
material such as feature films and for
the physical distribution of video games
for the PlayStation 3, PlayStation 4 and
Xbox One. The name “Blu-ray” refers
to the blue laser (actually a violet laser)
used to read the disc, which allows
information to be stored at a greater
density than is possible with the longerwavelength red laser used for DVDs.

Blocked rotor test
A blocked rotor test is conducted on an
induction motor. It is also known as short
circuit test, locked rotor test or stalled
torque test. From this test, short circuit
current at normal voltage, power factor
on short circuit, total leakage reactance,
and starting torque of the motor can
be found. The test is conducted at low
voltage because if the applied voltage
was normal voltage then the current
through the stator windings would be
high enough to overheat the windings
and damage them. The blocked rotor
torque test is not performed on woundrotor motors because the starting torque

Bode plot
In electrical engineering and control
theory, a Bode plot is a graph of the
frequency response of a system. It
is usually a combination of a Bode
magnitude plot, expressing the
magnitude (usually in decibels) of
the frequency response, and a Bode
phase plot, expressing the phase shift.
As originally conceived by Hendrik
Wade Bode in the 1930s, the plot is
an asymptotic approximation of the
frequency response, using straight line
segments.
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Boolean algebra (logic)
B

Boolean algebra is the branch of algebra
in which the values of the variables are
the truth values true and false, usually
denoted 1 and 0 respectively.

Boost converter

Bound charge

A boost converter (step-up converter)
is a DC-to-DC power converter that
steps up voltage (while stepping down
current) from its input (supply) to its
output (load). It is a class of switchedmode power supply (SMPS) containing
at least two semiconductors (a diode
and a transistor) and at least one
energy storage element: a capacitor,
inductor, or the two in combination.
To reduce voltage ripple, filters made
of capacitors (sometimes in combination
with inductors) are normally added to
such a converter’s output (load-side
filter) and input (supply-side filter).

In classical electromagnetism,
polarization density (or electric
polarization, or simply polarization)
is the vector field that expresses the
density of permanent or induced electric
dipole moments in a dielectric material.
When a dielectric is placed in an external
electric field, its molecules gain electric
dipole moment and the dielectric is
said to be polarized. The electric dipole
moment induced per unit volume of the
dielectric material is called the electric
polarization of the dielectric.

Braking chopper
Braking choppers sometimes also
referred to as braking unit are used in
the DC voltage intermediate circuits of
frequency converters to control voltage
when the load feeds energy back to
the intermediate circuit. This arises, for
example, when a magnetized motor is
being rotated by an overhauling load
and so functions as a generator feeding
power to the DC voltage intermediate
circuit. They are an application of the
chopper principle, using on-off control
of a switching device.

Booster (electric power)
A booster was a motor-generator (MG)
set used for voltage regulation in direct
current (DC) electrical power circuits.
The development of alternating current
and solid-state devices has rendered
it obsolete. Boosters were made in
various configurations to suit different
applications.

Breakdown voltage
The breakdown voltage of an insulator

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is the minimum voltage that causes
a portion of an insulator to become
electrically conductive. For diodes, the
breakdown voltage is the minimum
reverse voltage that makes the diode
conduct appreciably in reverse. Some
devices (such as TRIACs) also have a
forward breakdown voltage.

Bridge rectifier
A Bridge rectifier is an Alternating
Current (AC) to Direct Current (DC)
converter that rectifies mains AC input
to DC output. Bridge Rectifiers are
widely used in power supplies that
provide necessary DC voltage for the
electronic components or devices. They
can be constructed with four or more
diodes or any other controlled solidstate switches.

Buffer
An amplifier used to isolate a load from B
a source.

Broadcasting
Broadcasting is the distribution of audio
or video content to a dispersed audience
via any electronic mass communications
medium, but typically one using the
electromagnetic spectrum (radio waves),
in a one-to-many model. Broadcasting
began with AM radio, which came into
popular use around 1920 with the spread
of vacuum tube radio transmitters
and receivers. Before this, all forms of
electronic communication (early radio,
telephone, and telegraph) were one-toone, with the message intended for a
single recipient. The term broadcasting
evolved from its use as the agricultural
method of sowing seeds in a field by
casting them broadly about. It was later
adopted for describing the widespread
distribution of information by printed
materials or by telegraph.

Brush (electric)
A brush is a device which conducts
current between stationary wires and
moving parts, most commonly in a
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B

rotating shaft. Typical applications
include electric motors, alternators and
electric generators.

Brushless DC electric
motor

Brushed DC electric motor

Brushless DC electric motor (BLDC
motors, BL motors) also known as
electronically commutated motors
(ECMs, EC motors), or synchronous
DC motors, are synchronous motors
powered by DC electricity via an
inverter or switching power supply
which produces an AC electric current
to drive each phase of the motor via a
closed loop controller. The controller
provides pulses of current to the motor
windings that control the speed and
torque of the motor.

A brushed DC motor is an internally
commutated electric motor designed
to be run from a direct current power
source. Brushed motors were the first
commercially important application of
electric power to driving mechanical
energy, and DC distribution systems
were used for more than 100 years
to operate motors in commercial and
industrial buildings. Brushed DC motors
can be varied in speed by changing
the operating voltage or the strength
of the magnetic field. Depending on
the connections of the field to the
power supply, the speed and torque
characteristics of a brushed motor can be
altered to provide steady speed or speed
inversely proportional to the mechanical
load. Brushed motors continue to be
used for electrical propulsion, cranes,
paper machines and steel rolling mills.
Since the brushes wear down and
require replacement, brushless DC
motors using power electronic devices
have displaced brushed motors from
many applications.

Buchholz relay
In the field of electric power distribution
and transmission, a Buchholz relay is
a safety device mounted on some oilfilled power transformers and reactors,
equipped with an external overhead oil
reservoir called a “conservator”. The
Buchholz relay is used as a protective
device sensitive to the effects of dielectric
failure inside the equipment. A generic
designation for this type of device is
“gas detector relay”.

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voltage magnitude that is either greater
than or less than the input voltage
magnitude. It is equivalent to a flyback B
converter using a single inductor instead
of a transformer. Two different topologies
are called buck–boost converter. Both of
them can produce a range of output
voltages, ranging from much larger
(in absolute magnitude) than the input
voltage, down to almost zero.

Buck converter
A buck converter (step-down converter)
is a DC-to-DC power converter which
steps down voltage (while stepping up
current) from its input (supply) to its
output (load). It is a class of switchedmode power supply (SMPS) typically
containing at least two semiconductors (a
diode and a transistor, although modern
buck converters frequently replace the
diode with a second transistor used for
synchronous rectification) and at least
one energy storage element, a capacitor,
inductor, or the two in combination. To
reduce voltage ripple, filters made of
capacitors (sometimes in combination
with inductors) are normally added to
such a converter’s output (load-side
filter) and input (supply-side filter).

Buck–boost converter
The buck–boost converter is a type of
DC-to-DC converter that has an output

Buck–boost transformer
A buck–boost transformer is a type of
transformer used to make adjustments to
the voltage applied to alternating current
equipment. Buck–boost connections
are used in several places such as
uninterruptible power supply (UPS)
units for computers and in the tanning
bed industry. Buck–boost transformers
can be used to power low voltage
circuits including control, lighting
circuits, or applications that require 12,
16, 24, 32 or 48 volts, consistent with
the design’s secondary. The transformer
is connected as an isolating transformer
and the nameplate kVA rating is the
transformer’s capacity.

Building codes
A building code (also building control or
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B

building regulations) is a set of rules that
specify the standards for constructed
objects such as buildings and nonbuilding structures. Buildings must
conform to the code to obtain planning
permission, usually from a local council.
The main purpose of building codes is to
protect public health, safety and general
welfare as they relate to the construction
and occupancy of buildings and
structures. The building code becomes
law of a particular jurisdiction when
formally enacted by the appropriate
governmental or private authority.

Bunching
Bunching is the combining of multiple
odd-lot or round-lot orders for the same
security so that they can all be executed
at the same time. All affected clients
must agree to the bunching before the
order is submitted. Bunched trades may
also be referred to as block trades.

Buried layer

Bulk acoustic waves (BAWs) are
elastic waves propagating in solids.

Buried layers are formed within
a semiconductor. Metallic or
insulating buried layers are produced
several microns within a semiconductor
substrate. The buried layer can confine
current to the buried layer itself by
using a conductive material to create
the buried layer.

Bulk properties

Burn-in

When describing a material, the term
“bulk properties” is often used to
differentiate, either intentionally or
unintentionally, from the term “surface
properties.”

Burn-in is a test in which a system
or component is made to run for an
extended period of time to detect
problems.

Bulk acoustic wave

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B

Busbar

Bus network

In electric power distribution, a busbar
(also bus bar, and sometimes misspelled
as buss bar or bussbar) is a metallic
strip or bar, typically housed inside
switchgear, panel boards, and busway
enclosures for local high current power
distribution. They are also used to
connect high voltage equipment at
electrical switchyards, and low voltage
equipment in battery banks. They
are generally uninsulated, and have
sufficient stiffness to be supported in air
by insulated pillars. These features allow
sufficient cooling of the conductors, and
the ability to tap in at various points
without creating a new joint.

A bus network is a network topology
in which nodes are directly connected
to a common half-duplex link called a
bus. A host on a bus network is called a
station. In a bus network, every station
will receive all network traffic, and the
traffic generated by each station has
equal transmission priority.

Butterworth filter

Bushing (electrical)
In electric power, a bushing is an
insulated device that allows an electrical
conductor to pass safely through a
grounded conducting barrier such as
the case of a transformer or circuit
breaker. Bushings are typically made
from porcelain, though other materials
are possible.

The Butterworth filter is a type of signal
processing filter designed to have a
frequency response as flat as possible
in the pass band. It is also referred to
as a maximally flat magnitude filter.
It was first described in 1930 by the
British engineer and physicist Stephen
Butterworth in his paper entitled “On
the Theory of Filter Amplifiers”.

Buzzer
A buzzer or beeper is an audio signalling
device, which may be mechanical,
electromechanical, or piezoelectric (piezo
for short). Typical uses of buzzers and
beepers include alarm devices, timers,
and confirmation of user input such as
a mouse click or keystroke.
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Byte
B

The byte is a unit of digital information
that most commonly consists of eight
bits. Historically, the byte was the
number of bits used to encode a single
character of text in a computer and for
this reason it is the smallest addressable
unit of memory in many computer
architectures.

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Cc
Cable
An assembly of one or more insulated
conductors, or optical fibers, or
a combination of both, within an
enveloping jacket. Either a stranded
conductor (single-conductor cable) or
a combination of conductors insulated
from one another (multiple conductor
cable). Small sizes are commonly
referred to as stranded wire or as
cords. A conductor with insulation, or
a stranded conductor with or without
insulation and other coverings (singleconductor cable), or a combination of
conductors insulated from one another
(multiple-conductor cable).

Cable Assembly
A cable that is ready for installation
in specific applications and usually
terminated with connectors.

Cable Carrier
A device that holds a cable. Also refer
to a detailed definition of Cable Carrier.
In some case it may be called a cable
retractor.

Cable Clamp

Cable Armor
A covering of steel, wire, tape or some
other material used to protect the
internal conductors.

A mechanical clamp attached to the wire
entrance of a connector to support the
cable or wire bundle, provide stress
relief, and absorb vibration and shock.
Also called a cable adapter bracket. Flat
to round shown.

Cable Harness
A string of cables and/or wires which
transmit informational signals or
operating currents (energy). The cables
are bound together by clamps, cable
ties, cable lacing, sleeves, electrical tape,
conduit, a weave of extruded string, or
a combination thereof.

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C

Cable Leakage
Shielded cables with gaps in their
shielding, which allows the center
conductor to radiate. Cable signal leaks
can be caused by loose connectors, or
cracked or unterminated cables.

Cable Tray

A PC modem which interfaces between a
personal computer and a cabled internet
connection, normally coax. Related
topics; Modem IC Manufacturers, or
Modem Gear Manufacturers.

A lattice work or mesh of intersecting
metal used to support some number of
cables running between different points.
A cable tray is normally metal but may
also be plastic or fiber-glass. Cable Trays
may also be a solid section of metal
instead of a wire frame work.

Cable Splitter

Cache

See Splitter as it refers to a 3-port
component, or Y-Cable as it refers to a
cable with 3 ends or terminations.

A small portion of memory used as
temporary storage, normally having a
faster access time than the main memory
bank. A high-speed memory used to
stored data that was most recently
accessed by a processor.

Cable Modem

Cache memory
Cache memory is used to reduce the
average time to access data from the
Main memory.

Cable tester
A cable tester is an electronic device used
to verify the electrical connections in a
signal cable or other wired assembly.
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C

Can Bus
Cage Code
Commercial and Government Entity
Code. A five-position alphanumeric
code with a numeric in the first and last
positions (e.g. 27340, 2A345, or 2AAA5),
assigned to United States and Canadian
organizations which manufacture and/
or control the design of items supplied
to a Government Military or Civil
Agency or assigned to United States
and foreign organizations, primarily for
identifying contractors in the mechanical
interchange of data.

A differential 2-wire interface running
over either a Shielded Twisted Pair
(STP), Un-shielded Twisted Pair (UTP),
or Ribbon cable. A number of different
Protocols are used with CAN bus.
The CanBus is primarily used as an
Automotive Bus, but is also one of the
major Field Buses.

Cancel Character
A control character used by some
conventions to indicate that the data
with which it is associated are in error
or are to be disregarded. Related; Table
of ASCII Codes.

Calibration

Capacitance

Calibration is the process of configuring
an instrument to provide a result for
a sample within an acceptable range.
Eliminating or minimizing factors that
cause inaccurate measurements is a
fundamental aspect of instrumentation
design.

The property of an electrical circuit that
opposes changes in voltage. Also refer
to the dictionary of Capacitor Terms.
That property of a system of conductors
and dielectrics that permits the storage
of electricity when potential difference
exists between the conductors. Its value
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electrical energy in an electrostatic field.

is expressed as the ratio of quantity of
electricity to a potential difference. A
capacitance value is always positive.
C

Capacitor Microphone

Capacitive Coupling

A microphone that uses one plate of a
capacitor as the diaphragm.

The transfer of energy from one circuit
to another by means of the mutual
capacitance between the circuits. Detailed
definition of Capacitive Coupling.

Capacitor-Start Motor
A type of single-phase, ac induction
motor in which a starting winding
and a capacitor are placed in series to
start the motor. The values of XC and
R are such that the main-winding and
starting-winding currents are nearly 90
degrees apart and the starting torque
is produced as in a two-phase motor.

Capacitive Load
A load where the current leads the
voltage.

Capacitive Reactance
The opposition, expressed in ohms,
offered to the flow of an alternating
current by capacitance. The symbol for
capacitive reactance is XC.

Capture Ratio

Capacitor

A measure of an FM tuner’s ability to
reject an interfering signal of the same
frequency as the desired signal.

An electrical device capable of storing
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Carbon-film resistor
Carbon film resistors are a type of fixed
value resistor. They are constructed out
of a ceramic carrier with a thin pure
carbon film around it. This carbon
film functions as the resistive material.

or slots and allows attachment of a
backplane to allow the interconnection
of the cards within the cage.

Card Extractor
A device specifically designed to remove
a circuit card assembly.

Carbon Microphone
A microphone in which sound waves
vary the resistance of a pile of carbon
granules. May be single-button or
double-button.

Card Stiffener
A rigid item mounted to a printed
wiring board.

Cardbus

Carbon Resistor

One of the different types of PCMCIA
interfaces. CardBus implements the 32bit PCI bus standard into the PCMCIA
form factor.

A resistor that uses either a slug of
carbon or a film impregnated with
carbon as the resistive element.

Card Cage
That portion of an equipment chassis
that holds the circuit cards. An open
or closed frame which has card guides
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Carrier
C

A constant amplitude wave that may
be modulated in amplitude, frequency
or phase.

Carrier Card

Cartridge Fuse

A host card designed to hold two or
more mezzanine cards, and having the
primary function of supporting the cards
by providing a site for the mezzanine
card. The VME card to the right acts
as a carrier card for one or two PMC
mezzanine cards which would plug into
the pair of black connectors just to the
right of the white VME connector.

An instrument fuse. A fuse with a
cylindrical body usually made of plastic
or ceramic and terminated with metal
end caps. Also called a ribbon fuse when
the body of the fuse is glass.

Cascade Amplifier

Carrier Frequency

Two or more amplifiers connected
together, with each output connected to
the input of the following stage. Several
amplifiers connected in series, forming
a chain.

The base frequency of a transmitted
electromagnetic pulse or wave on which
information can be imposed by varying
the signal strength, varying the base
frequency, varying the wave phase,
or other means. The frequency of an
unmodulated transmitter output.

Carrier Wave
The Carrier Frequency component of
a modulated wave, or the signal wave
that is intended to be modulated.

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Cascading

Circuit Breaker

Connecting two or more circuits together
so that one circuit feeds the other.

Safety device used to break the flow
of electricity by opening the circuit
automatically in the event of overloading,
or used to open or close it manually.

Case Temperature
The temperature measured at a specified
point on the case of a semiconductor
device.

Cathode
A cathode is the electrode from which a
conventional current leaves a polarized
electrical device. This definition can be
recalled by using the mnemonic CCD for
Cathode Current Departs. A conventional
current describes the direction in which
positive charges move.

Computer aided design

Circuit

Computer-aided design (CAD) is a way
to digitally create 2D drawings and 3D
models of real-world products before
they’re ever manufactured. With 3D
CAD, you can share, review, simulate,
and modify designs easily, opening
doors to innovative and differentiated
products that get to market fast.

Flow of electricity through two or more
wires from the supply source to one or
more outlets and back to the source.

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Computer aided
manufacturing
C

C o m p u t e r- a i d e d m a n u f a c t u r i n g
(CAM) is a type of manufacturing
method that uses computer software
and automatable machinery to create
products with a high degree of accuracy
and precision. Modern machines and
software technologies have enabled us
to create better parts with increasingly
more control over the entire process.

Common collector
A common collector amplifier (also
known as an emitter follower) is one of
three basic single-stage bipolar junction
transistor (BJT) amplifier topologies,
typically used as a voltage buffer.
In this circuit the base terminal of
the transistor serves as the input, the
emitter is the output, and the collector
is common to both (for example, it may
be tied to ground reference or a power
supply rail), hence its name. The
analogous field-effect transistor circuit
is the common drain amplifier and the
analogous tube circuit is the cathode
follower.

Common base
configuration
Common Base (CB) configuration (or)
Grounded base configuration. In this
circuit arrangement, input is applied
between the emitter and base, and
output is taken from the collector and
base. Here, the base of the transistor
is common to both input and output
circuits and hence the name common
base connection.

Common emitter
A common-emitter amplifier is one of
three basic single-stage bipolar-junctiontransistor (BJT) amplifier topologies,
typically used as a voltage amplifier.
It offers high current gain (typically
200), medium input resistance and a
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high output resistance. The output
of a common emitter amplifier is 180
degrees out of phase to the input signal.

a computer program, such as arithmetic,
logic, controlling, and input/output (I/O)
operations. This role contrasts with that
of external components, such as main
memory and I/O circuitry,[1] and
specialized coprocessors such
as graphics processing units (GPUs).

cmil
A circular mil is a unit of area, equal to
the area of a circle with a diameter of
one mil (one thousandth of an inch
or 0.0254 mm). It corresponds to
approximately 5.067×10−4 mm2. It is a
unit intended for referring to the area
of a wire with a circular cross section.
As the definition of the unit contains π,
it is easy to calculate area values in
circular mils when the diameter in mils
is known.

Conductor
The internal material of a cord that
conducts electricity. Copper is the most
common material used for electrical
wiring. Silver is the best conductor,
but is expensive. Because it does not
corrode, gold is used for high-quality
surface-to-surface contacts.

Conductor Gauge

Central processing unit
A
central
processing
unit (CPU)—also called a central
processor or main processor—is
the most important processor in
a given computer. Its electronic
circuitry executes instructions of

Numerical system used to label electric
conductor sizes, given in American Wire
Gauge (AWG) or square millimeters
diameter.

Connector
A female cord mounted wiring device
with the conducting elements recessed
behind the mating surface. This type of
device is normally wired to be live when
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CRT

nothing is plugged in to it. Therefore,
connectors are wired to the source of
power.

A Cathode–Ray Tube is a vacuum tube
containing one or more electron guns,
which emit electron beams that are
manipulated to display images on a
phosphorescent screen. The images may
represent electrical waveforms, pictures,
radar targets, or other phenomena. A
CRT on a television set is commonly
called a Picture Tube.

C

Covered Conductor
Wire or cable covered with one or more
layers of insulation.

CRO
CSA

The CRO stands for a cathode ray
oscilloscope. It is typically divided into
four sections which are display, vertical
controllers, horizontal controllers, and
Triggers. Most of the oscilloscopes are
used the probes and they are used for the
input of any instrument. We can analyze
the waveform by plotting amplitude
along with the x-axis and y-axis. The
applications of CRO are mainly involved
in the radio, TV receivers, also in
laboratory work involving research and
design. In modern electronics, the CRO
plays an important role in the electronic
circuits.

Canadian Standards Association, a
Canadian product safety and certification
organization. Their registered mark
shows that a product has been
independently tested and certified to
meet recognized standards for safety
or performance.

Current
The rate of flow of electrical energy
through a conductor or wire, comparable
to the amount of water flowing in a
pipe. Electric current is measured in
amperes or “amps”.

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Current gain

Cut-off frequency

The current gain for the common-base
configuration is defined as the change in
collector current divided by the change
in emitter current when the base-tocollector voltage is constant.

A cutoff frequency, corner frequency,
or break frequency is a boundary in a
system’s frequency response at which
energy flowing through the system
begins to be reduced rather than passing
through.

Current transformer
A current transformer is a type of
transformer that is used to reduce
or multiply an alternating current. It
produces a current in its secondary
which is proportional to the current in
its primary. Current transformers, along
with voltage or potential transformers,
are instrument transformers.

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Dd
D’Arsonval galvanometer
D

D’Arsonval galvanometer, in which the
indicating system consists of a light
coil of wire suspended from a metallic
ribbon between the poles of a permanent
magnet.

D Flip Flop
A style of flip flop who’s output follows
the input when the device is clocked.
The Truth Table for a D-Type flip flop is
shown to the right. The output changes
on the edge of the clock. The most
common IC is the 7474; Dual PositiveEdge-Triggered D-Type Flip-Flops with
Set and Reset.

Daisy Chain
An interconnection architecture that
connects components in a line, one
after the other. An Interface Bus
Architecture where one node on the
bus feeds only one other node and
only receives information from only
one node.

D-region
The D-region of the ionosphere,
traditionally defined as the region of
ionization below 100 km, is a link
between the non-ionized stratosphere
below and the dense plasma above. In
it, minor neutral constituents play a
dominant role and chemical reactions,
both neutral and ionic, are dominant.

Damping
The process of smoothing out oscillations.
The progressive decay with time in the
amplitude of the free oscillations in a
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circuit. The progressive diminution with
time of certain quantities characteristic of
a phenomenon. In a meter, this process
is used to keep the pointer of the meter
from over-shooting the correct reading.
A mechanical or electrical technique
used in synchro receivers to prevent
the rotor from oscillating or spinning.
Damping is also used in servo systems
to minimize overshoot of the load.

Darlington
A transistor pair configured as a
dual Emitter amplifier. A transistor
configuration that produces a gain equal
to the product of both transistors. A
transistor pair in which the emitter
current of the first transistor equals the
Base current of the second transistor.

D’Arsonval Meter
Movement
The permanent-magnet moving-coil
movement used in most analog meters.
Note that most meters use digital
displays. A common Analog meter
movement is shown to the right.

Damped Natural
Frequency
The frequency of an oscillator or other
circuit that occurs following a transient
input, which might be a step function.

Damped Oscillation

Data Bandwidth

An Oscillation that gradually decreases
over time.

The difference between the highest
and lowest frequency of the data to
be transmitted, usually defined by the
-3dB points.

Damped Wave
A sinusoidal wave in which the
amplitude steadily decreases with time.
Often associated with energy loss.

Damping Coefficient
The ratio of damping to critical damping.

Data Block
A block transfer that moves a unit
of data as a complete unit, normally
without much of the associated overhead
required with a single data transfer. Any
required interaction to gain control of an
interface bus is only done with the first
data transfer, while all other transfers
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be stored in a given domain, such as
space, time, or frequency, or contained
in a given message length. Reducing the
amount of storage space required to store
a given amount of data, or reducing the
length of message required to transfer
a given amount of information.

within the block do not require this
over-head.

D

Data Conversion

Data Bus

The process of changing data from one
form of representation to another.

A bus used to transfer data within or to
and from a processing unit or storage
device.

Data Encryption Standard
A cryptographic algorithm for the
protection of unclassified computer
data and published by the National
Institute of Standards and Technology
in Federal Information Processing
Standard Publication 46-1.

Data Communication
The transfer of information between
functional units by means of data
transmission according to a protocol.

Data Compaction

Data Frame

The reduction of the number of data
elements, bandwidth, cost, and time for
the generation, transmission, and storage
of data without loss of information by
eliminating unnecessary redundancy,
removing irrelevancy, or using special
coding.

A packet of transmitted information that
contains at a minimum, the destination
address and information being
transmitted. Additional information
also being transmitted may include the
source address, a check word or CRC,
and frame length.

Data Compression

Data Integrity

Increasing the amount of data that can

The condition in which data are
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identically maintained during any
operation, such as transfer, storage, and
retrieval.

or blocks per unit time passing between
corresponding equipment in a data
transmission system.

Data Link

Data Transmission

The means of connecting one location to
another for the purpose of transmitting
and receiving data. The communication
path between nodes on a network.

The transfer of information from one
place to another or from one part of a
system to another. The sending of data
from one place to another by means of
signals over a channel.

Data Multiplexing
The process of combining two or more
signals into a single composite signal.

Datum
Data Processing
The execution of a systematic sequence
of operations performed upon data.
Synonymous with information
processing.

Data Signaling Rate
The aggregate rate at which data pass
a point in the transmission path of a
data transmission system.

A datum is the origin from which the
location or geometric characteristics of
features of a part are established.

DC – Direct Current
Current which moves in a single
direction in a steady flow. Normal
household electricity is alternating
current (AC) which repeatedly reverses
its direction. However, many electronics
devices require DC, and therefore must
convert the current into DC before using
it.

Data Transfer Rate
The average number of bits, characters,
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materials and spacing under normal
conditions.

D

Dielectric
Any insulating medium, which
intervenes between two conductors
and permits electrostatic attraction and
repulsion to take place across it.

Digital/Analogue Converter
(DAC)
A device used to generate a replica of the
original analogue signal that has been
coded into binary data and transmitted
as a digital signal.

Diode

Dielectric constant

A semiconductor device with two
terminals, typically allowing the flow
of current in one direction only. Diodes
allow current to flow when the anode
is positive in relation to the cathode.

A quantity measuring the ability of a
substance to store electrical energy in
an electric field.

Dielectric strength
The maximum electric field that a pure
material can withstand under ideal
conditions without breaking down
(i.e., without experiencing failure of its
insulating properties).

Dielectric Test
Tests which consist of the application of
a voltage higher than that of the rated
voltage for a specified time for the
purpose of determining the adequacy
against breakdown of insulating

DIP
Dual in-line package. A rectangular
electronic component with parallel pins
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on both sides. These packages can be
soldered directly to the PCB or inserted
in a socket.

Dynamo
A dynamo is an electrical generator
that creates direct current using a
commutator.
D

Direct-quadrature-zero
transformation
The direct-quadrature-zero (DQZ or
DQ0 or DQO, sometimes lowercase)
transformation or zero-direct-quadrature
(0DQ or ODQ, sometimes lowercase)
transformation is a tensor that rotates
the reference frame of a three-element
vector or a three-by-three element
matrix in an effort to simplify analysis.
The DQZ transform is the product of
the Clarke transform and the Park
transform, first proposed in 1929 by
Robert H. Park. The DQZ transform is
often used in the context of electrical
engineering with three-phase circuits.
The transform can be used to rotate the
reference frames of ac waveforms such
that they become dc signals. Simplified
calculations can then be carried out on
these dc quantities before performing
the inverse transform to recover the
actual three-phase ac results. As an
example, the DQZ transform is often
used in order to simplify the analysis
of three-phase synchronous machines or
to simplify calculations for the control
of three-phase inverters. In analysis of
three-phase synchronous machines the
transformation transfers three-phase
stator and rotor quantities into a single
rotating reference frame to eliminate
the effect of time-varying inductances.

Dyne
The dyne is a derived unit of force
specified in the centimetre–gram–second
system of units, a predecessor of the
modern SI.

Dynode
A dynode is an electrode in a vacuum
tube that serves as an electron multiplier
through secondary emission. The first
tube to incorporate a dynode was the
dynatron, an ancestor of the magnetron,
which used a single dynode.

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Ee

Early voltage
The Early voltage is a parameter
describing the variation of the transistor
collector or drain current in the active or
the saturation region of operation with
the VCE or VDS , respectively.

E-layer
E

The E layer is the middle layer, 90 km (56
mi) to 150 km (93 mi) above the surface
of the Earth. Ionization is due to soft
X-ray (1–10 nm) and far ultraviolet (UV)
solar radiation ionization of molecular
oxygen (O2).

EAROM
Acronym for electrically alterable readonly memory. A form of semiconductor
memory in which it is possible to
change the contents of selected memory
locations by applying suitable electric
signals. Normally these changes are
infrequent.

E-plane
The electric field or “E” plane determines
the polarization or orientation of the
radio wave.

E-region

Earphone

E region, also called Kennelly-Heaviside
Layer, ionospheric region that generally
extends from an altitude of 90 km (60
miles) to about 160 km (100 miles).

A transducer placed near the ear or over
the ear. A small speaker placed over
one or both ears. A smaller version of
Headphones.

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code for alphabetic and numeric
characters that IBM developed for its
larger operating systems. It is the code
for text files that is used in IBM’s OS/390
operating system for its S/390 servers and
that thousands of corporations use for
their legacy applications and databases.
In an EBCDIC file, each alphabetic or
numeric character is represented with
an 8-bit binary number (a string of eight
0’s or 1’s). 256 possible characters (letters
of the alphabet, numerals, and special
characters) are defined.

Earth Ground
The connection to earth. Ground. The
most common connection to earth is via
a water pipe. The graphic shows how to
connect a Printed Circuit Board [PCB]
ground to chassis ground. In many cases
chassis ground will also connect to earth
ground.

ECG
An electrocardiogram (ECG or
EKG) records the electrical signal from
the heart to check for different heart
conditions. Electrodes are placed on
the chest to record the heart’s electrical
signals, which cause the heart to beat.

Echo
The reflection of the original sound
wave as it bounces off a distant surface.
The RF signal reflected back from a
radar target.

EBCDIC
EBCDIC (Extended Binary Coded
Decimal Interchange Code) is a binary
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Echo Box

E

The normal supply voltage level [Vee] is
-5.2 volts as opposed to TTL logic which
is 5 volts. However ECL also uses a Vcc
of between 0 volts to 7 volts. Although
ECL ‘logic’ gates function the same as
TTL gates, the greater speed, differential
un-saturated logic [analog] signals and
impedance matching requirements
impose a completely different design
approach.

A resonant cavity device that is used
to check the overall performance of a
radar system. It receives a portion of
the transmitted pulse and retransmits it
back to the receiver as a slowly decaying
transient.

E-Core
E-Cores expose the winding so heat does
not get trapped inside and also makes
it easier to bring out connections from
several windings.

ECL
[Emitter Coupled Logic] A type of
digital logic using transistors that do
not go into saturation, allowing the
devices to operate faster [as it takes
longer for the transistor to come out of
saturation]. For more detail on switching
speed, ECL circuit diagram and logic
family comparisons. An ECL OR gate
symbol is shown to the right. Note that
most gates use differential inputs and
outputs, although the I/O can be made
into single ended lines too.

Eddy Current Loss
Losses caused by random current
flowing in the core of a transformer.
Power is lost in the form of heat.

Eddy Current
Induced circulating currents in a
conducting material that are caused by
a varying magnetic field. The current
induced in a conductor subjected to a
varying magnetic field.

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Edge Triggered Flip Flop
A type of Flip Flop [FF] that requires
either a rising edge or falling edge of a
clock edge to force the output to change
to the level of the input signal [D].
E

Edge Connector
A male connector formed by running
conductive copper traces to the edge of
a printed wiring board to act as a plug
for another connector. The standard
connector system used for expansion
cards in personal computers.

Edge Triggering
A method of activating a circuit by
means of a pulse transition from either
high to low or low to high. Normally
components such as flip flops are edge
triggered while components like latches
are level triggered.

Edge Skew
The difference in the arrival between
two edges from the same device. For a
flip flop, the difference in time between
when Q output goes high and the Q-bar
output goes low. The difference in time
between the outputs of a digital counter
changing, with reference to each other
[A, B, C, D].

Edison Cell
Another name for a nickel-iron cell or
battery [NiFe].

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EHF
Extremely high frequency (EHF) is the
International Telecommunication Union
(ITU) designation for the band of radio
frequencies in the electromagnetic
spectrum from 30 to 300 gigahertz
(GHz). It lies between the super high
frequency band and the far infrared
band, the lower part of which is the
terahertz band.

E

Edison Effect
Also called Richardson Effect. The
phenomenon wherein electrons emitted
from a heated element within a vacuum
tube will flow to a second element that
is connected to a positive potential.

Electricity
Energy used to run household appliances
and industrial machinery; can produce
light, sound, heat and numerous other
uses.

eDRAM
Embedded DRAM [Memory]. eDRAM
is used as embedded memory blocks
within ASIC ICs. eDRAM does not exist
as an individual integrated circuit, IC
or component.

Electrolyte
Any substance which, in solution, is
dissociated into ions and is thus made
capable of conducting an electrical
current. The sulfuric acid - water solution
in a storage battery is an electrolyte.

Electromotive Force (EMF)
Electromotive force, abbreviated emf,
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is the electrical intensity or “pressure”
developed by a source of electrical
energy such as a battery or generator.
A device that converts other forms
of energy into electrical energy (a
“transducer”) provides an emf at its
output. (The word “force” in this case
is not used to mean mechanical force,
as may be measured in pounds or
newtons.).

E

EMI
Electromagnetic interference (EMI)
is unwanted noise or interference in
an electrical path or circuit caused by
an outside source. It is also known as
radio frequency interference. EMI can
cause electronics to operate poorly,
malfunction or stop working completely.

Electron
A tiny particle which rotates around the
nucleus of an atom. It has a negative
charge of electricity.

EW
Electronic warfare is warfare involving
the use of the electromagnetic spectrum
or directed energy to control the
spectrum, attack an enemy, or impede
enemy operations.

Electron theory
The theory which explains the nature
of electricity and the exchange of “free”
electrons between atoms of a conductor.
It is also used as one theory to explain
direction of current flow in a circuit.
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Ff
F-layer

F

The F layer or region, also known as
the Appleton–Barnett layer, extends
from about 150 km (93 mi) to more
than 500 km (310 mi) above the surface
of Earth. It is the layer with the highest
electron density, which implies signals
penetrating this layer will escape into
space.

Faraday shield
A Faraday cage or Faraday shield is an
enclosure used to block electromagnetic
fields. A Faraday shield may be formed
by a continuous covering of conductive
material or in the case of a Faraday cage,
by a mesh of such materials. Faraday
cages are named after the English
scientist Michael Faraday, who invented
them in 1836.

F-region
The F region of the ionosphere is home
to the F layer of ionization, also called
the Appleton–Barnett layer, after the
English physicist Edward Appleton
and New Zealand physicist and
meteorologist Miles Barnett.

Faraday’s law of induction

Farad

Faraday’s law of induction is a basic
law of electromagnetism predicting
how a magnetic field will interact
with an electric circuit to produce
an electromotive force (EMF)—a
phenomenon called electromagnetic
induction. It is the fundamental
operating principle of transformers,
inductors, and many types of electrical
motors, generators and solenoids.

The farad (symbol: F) is the SI derived
unit of electrical capacitance, the ability
of a body to store an electrical charge.
It is named after the English physicist
Michael Faraday.

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Fast Fourier Transform

Fax

A fast Fourier transform (FFT) is an
algorithm that samples a signal over a
period of time (or space) and divides
it into its frequency components. These
components are single sinusoidal
oscillations at distinct frequencies each
with their own amplitude and phase.
This transformation is illustrated in
Diagram 1. Over the time period
measured, the signal contains 3 distinct
dominant frequencies.

Fax (short for facsimile), sometimes
called telescoping or telefax (the latter
short for telefacsimile), is the telephonic
transmission of scanned printed material
(both text and images), normally to a
telephone number connected to a printer
or other output device. The original
document is scanned with a fax machine
(or a telecopier), which processes the
contents (text or images) as a single
fixed graphic image, converting it into a
bitmap, and then transmitting it through
the telephone system in the form of
audio-frequency tones. The receiving
fax machine interprets the tones and
reconstructs the image, printing a
paper copy. Early systems used direct
conversions of image darkness to audio
tone in a continuous or analog manner.
Since the 1980s, most machines modulate
the transmitted audio frequencies using
a digital representation of the page
which is compressed to quickly transmit
areas which are all-white or all-black.

Fault (power engineering)
In an electric power system, a fault or
fault current is any abnormal electric
current. For example, a short circuit
is a fault in which current bypasses
the normal load. An open-circuit fault
occurs if a circuit is interrupted by some
failure. In three-phase systems, a fault
may involve one or more phases and
ground, or may occur only between
phases. In a “ground fault” or “earth
fault”, current flows into the earth.
The prospective short-circuit current
of a predictable fault can be calculated
for most situations. In power systems,
protective devices can detect fault
conditions and operate circuit breakers
and other devices to limit the loss of
service due to a failure.

Feed forward (control)
Feed-forward, sometimes written feed
forward, is a term describing an element
or pathway within a control system
that passes a controlling signal from a
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F

source in its external environment, often
a command signal from an external
operator, to a load elsewhere in its
external environment. A control system
which has only feed-forward behavior
responds to its control signal in a predefined way without responding to how
the load reacts; it is in contrast with a
system that also has feedback, which
adjusts the output to take account of
how it affects the load, and how the load
itself may vary unpredictably; the load
is considered to belong to the external
environment of the system.

Feed-in tariff
A feed-in tariff (FIT, FiT, standard offer
contract, advanced renewable tariff, or
renewable energy payments) is a policy
mechanism designed to accelerate
investment in renewable energy
technologies. It achieves this by offering
long-term contracts to renewable energy
producers, typically based on the cost
of generation of each technology. Rather
than pay an equal amount for energy,
however generated, technologies such as
wind power and solar PV, for instance,
are awarded a lower per-kWh price,
while technologies such as tidal power
are offered a higher price, reflecting
costs that are higher at the moment.

Feedback
The return of a portion of the output,
or processed portion of the output, of
a (usually active) device to the input.
The feedback may be in phase with the
input signal [positive feedback], or out
of phase with the input signal [negative
feedback].

Feedback amplifier

Ferrite core

A negative-feedback amplifier (or
feedback amplifier) is an electronic
amplifier that subtracts a fraction of its
output from its input, so that negative
feedback opposes the original signal. The
applied negative feedback can improve
its performance (gain stability, linearity,
frequency response, step response)
and reduces sensitivity to parameter
variations due to manufacturing
or environment. Because of these
advantages, many amplifiers and control
systems use negative feedback.

In electronics, a ferrite core is a type of
magnetic core made of ferrite on which
the windings of electric transformers
and other wound components such as
inductors are formed. It is used for its
properties of high magnetic permeability
coupled with low electrical conductivity
(which helps prevent eddy currents).
Because of their comparatively low losses
at high frequencies, they are extensively
used in the cores of RF transformers
and inductors in applications such as
switched-mode power supplies, and
ferrite loop stick antennas for AM radio
receivers.

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Ferroelectricity
Ferroelectricity is a characteristic of
certain materials that have a spontaneous
electric polarization that can be reversed
by the application of an external electric
field. All ferroelectrics are pyroelectric,
with the additional property that
their natural electrical polarization is
reversible. The term is used in analogy
to ferromagnetism, in which a material
exhibits a permanent magnetic moment.
Ferromagnetism was already known
when ferroelectricity was discovered in
1920 in Rochelle salt by Valasek. Thus,
the prefix ferro, meaning iron, was used
to describe the property despite the fact
that most ferroelectric materials do not
contain iron.

Fiber optic cable
An optical fiber cable, also known as
fiber optic cable, is an assembly similar
to an electrical cable, but containing one
or more optical fibers that are used to
carry light. The optical fiber elements are
typically individually coated with plastic
layers and contained in a protective tube
suitable for the environment where
the cable will be deployed. Different
types of cable are used for different
applications, for example long distance
telecommunication, or providing a highspeed data connection between different
parts of a building.

F

Field effect transistor
The field-effect transistor (FET) is a
transistor that uses an electric field
to control the electrical behavior of
the device. FETs are also known as
unipolar transistors since they involve
single-carrier-type operation. Many
different implementations of field
effect transistors exist. Field effect
transistors generally display very high
input impedance at low frequencies.
The conductivity between the drain
and source terminals is controlled by
an electric field in the device, which
is generated by the voltage difference
between the body and the gate of the
device.

Field-oriented control
Vector control, also called field-oriented
control (FOC), is a variable-frequency
drive (VFD) control method in which
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F

the stator currents of a three-phase
AC electric motor are identified as
two orthogonal components that can be
visualized with a vector. One component
defines the magnetic flux of the motor,
the other the torque. The control system
of the drive calculates the corresponding
current component references from
the flux and torque references given
by the drive’s speed control. Typically
proportional-integral (PI) controllers
are used to keep the measured current
components at their reference values.
The pulse-width modulation of the
variable-frequency drive defines the
transistor switching according to the
stator voltage references that are the
output of the PI current controllers.

filtering of undesirable frequencies. They
are common in electrical and electronic
equipment, and cover a number of
applications, such as:

►
►

►

►

Filter (signal processing)

►

In signal processing, a filter is a device
or process that removes some unwanted
components or features from a signal.
Filtering is a class of signal processing,
the defining feature of filters being the
complete or partial suppression of some
aspect of the signal. Most often, this
means removing some frequencies or
frequency bands. However, filters do
not exclusively act in the frequency
domain; especially in the field of
image processing many other targets
for filtering exist. Correlations can
be removed for certain frequency
components and not for others without
having to act in the frequency domain.
Filters are widely used in electronics and
telecommunication, in radio, television,
audio recording, radar, control systems,
music synthesis, image processing, and
computer graphics.

Glitch removal on Direct
current (DC) power rails
Radio frequency interference
(RFI) removal for signal
or power lines entering or
leaving equipment
Capacitors used after a
voltage regulator to further
smooth dc power supplies
Capacitors used in audio,
intermediate frequency (IF)
or radio frequency (RF)
frequency filters (e.g. low
pass, high pass, notch, etc.)
Arc suppression, such as
across the contact breaker or
‘points’ in a spark-ignition
engine

Filter capacitors are not the same
as reservoir capacitors, the tasks the
two perform are different, albeit related.

Finite impulse response
In signal processing, a finite impulse
response (FIR) filter is a filter whose
impulse response (or response to any
finite length input) is of finite duration,
because it settles to zero in finite time.

Filter capacitor
Filter capacitors are capacitors used for
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This is in contrast to infinite impulse
response (IIR) filters, which may have
internal feedback and may continue to
respond indefinitely (usually decaying).
The impulse response (that is, the output
in response to a Kronecker delta input)
of an Nth-order discrete-time FIR filter
lasts exactly N + 1 samples (from first
nonzero element through last nonzero
element) before it then settles to zero.

Firmware
In electronic systems and computing,
firmware is a computer program that
provides the low-level control for the
device’s specific hardware. Firmware
can either provide a standardized
operating environment for the device’s
more complex software (allowing
more hardware-independence), or,
for less complex devices, act as the
device’s complete operating system,
performing all control, monitoring and
data manipulation functions. Typical
examples of devices containing firmware
are embedded systems, consumer
appliances, computers, computer
peripherals, and others. Almost all
electronic devices beyond the simplest
contain some firmware.

Fleming oscillation valve, was a vacuum
tube (or “thermionic valve”) invented
in 1904 by John Ambrose Fleming as a
detector for early radio receivers used in
electromagnetic wireless telegraphy. It
was the first practical vacuum tube and
the first thermionic diode, a vacuum tube
whose purpose is to conduct current in
one direction and block current flowing
in the opposite direction. The thermionic
diode was later widely used as a rectifier
— a device which converts alternating
current (AC) into direct current (DC) —
in the power supplies of a wide range
of electronic devices, until beginning to
be replaced by the selenium rectifier in
the early 1930s and almost completely
replaced by the semiconductor diode in
the 1960s. The Fleming valve was the
forerunner of all vacuum tubes, which
dominated electronics for 50 years. The
IEEE has described it as “one of the
most important developments in the
history of electronics”, and it is on the
List of IEEE Milestones for electrical
engineering.

Fleming’s left-hand rule
for motors

Fleming valve
The Fleming valve, also called the

Fleming’s left-hand rule for motors is
one of a pair of visual mnemonics, the
other being Fleming’s right-hand rule
(for generators). They were originated
by John Ambrose Fleming, in the late
19th century, as a simple way of working
out the direction of motion in an electric
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field strength times the coil area. Flux
linkage is flux density x cross sectional
area x number of turns in coil Field
strength is technically different from
flux density, but I don’t think they care
too much at a-level.

motor, or the direction of electric current
in an electric generator.

Flyback converter
The flyback converter is used in both
AC/DC and DC/DC conversion with
galvanic isolation between the input and
any outputs. The flyback converter is a
buck-boost converter with the inductor
split to form a transformer, so that the
voltage ratios are multiplied with an
additional advantage of isolation. When
driving for example a plasma lamp or a
voltage multiplier the rectifying diode
of the boost converter is left out and the
device is called a flyback transformer.

F

Fluorescent lamp
A fluorescent lamp, or fluorescent tube,
is a low-pressure mercury-vapor gasdischarge lamp that uses fluorescence to
produce visible light. An electric current
in the gas excites mercury vapor, which
produces short-wave ultraviolet light
that then causes a phosphor coating
on the inside of the lamp to glow. A
fluorescent lamp converts electrical
energy into useful light much more
efficiently than incandescent lamps. The
typical luminous efficacy of fluorescent
lighting systems is 50–100 lumens per
watt, several times the efficacy of
incandescent bulbs with comparable
light output.

Flyback transformer
A flyback transformer (FBT), also called
a line output transformer (LOPT), is a
special type of electrical transformer. It
was initially designed to generate high
voltage saw tooth signals at a relatively
high frequency. In modern applications,
it is used extensively in switched-mode
power supplies for both low (3 V) and
high voltage (over 10 kV) supplies.

Flux linkage
Flux linkage is the magnetic flux running
through, or “linked” to a coil, so the
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Fossil-fuel phase-out

Fokker–Planck equation
Fokker–Planck equation is a partial
differential equation that describes the
time evolution of the probability density
function of the velocity of a particle
under the influence of drag forces and
random forces, as in Brownian motion.
The equation can be generalized to other
observables as well.

Forward converter
The forward converter is a DC/DC
converter that uses a transformer to
increase or decrease the output voltage
(depending on the transformer ratio)
and provide galvanic isolation for the
load. With multiple output windings, it
is possible to provide both higher and
lower voltage outputs simultaneously.

Fossil fuel phase out refers to the
discontinuation of the use of fossil
fuels, through the decommissioning of
operating fossil fuel-fired power plants,
the prevention of the construction of
new ones, and the use of alternative
energy to replace the role of fossil fuels.
The purpose of fossil fuel phase-out is to
reduce the negative externalities that use
of fossil fuels cause. Negative externalities
refer to the costs a certain activity has
over people who did not choose to incur
in them. A direct negative externality
from fossil fuels’ use is air pollution,
and an indirect negative externality
are mining accidents, that happen as a
consequence of the extraction of fossil
fuels. Fossil fuel burning contributes to
climate change, as it releases greenhouse
gas emissions.

Fossil-fuel power station
A fossil fuel power station is a power
station which burns a fossil fuel such
as coal, natural gas, or petroleum to
produce electricity. Central station fossil
fuel power plants are designed on a
large scale for continuous operation.
In many countries, such plants
provide most of the electrical energy
used. Fossil fuel power stations have
machinery to convert the heat energy
of combustion into mechanical energy,
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F

which then operates an electrical
generator. The prime mover may be
a steam turbine, a gas turbine or, in
small plants, a reciprocating internal
combustion engine. All plants use the
energy extracted from expanding gas,
either steam or combustion gases. Very
few MHD generators have been built
which directly convert the energy of
hot, moving water into electricity. MHD
means Magneto hydrodynamics, which
is the study of the magnetic properties of
electrically conducting fluids. Examples
of such magnetofluids include plasmas,
liquid metals, salt water and electrolytes.

Frequency
Frequency is the number of occurrences
of a repeating event per unit of time. It
is also referred to as temporal frequency,
which emphasizes the contrast to spatial
frequency and angular frequency. The
period is the duration of time of one
cycle in a repeating event, so the period
is the reciprocal of the frequency.

Frequency changer
A frequency changer or frequency
converter is an electronic or
electromechanical device that converts
alternating current (AC) of one
frequency to alternating current of
another frequency. The device may also
change the voltage, but if it does, that
is incidental to its principal purpose.

Free space optical
communications
Free-space optical communication
(FSO) is an optical communication
technology that uses light propagating
in free space to wirelessly transmit data
for telecommunications or computer
networking. “Free space” means air,
outer space, vacuum, or something
similar. This contrasts with using solids
such as optical fiber cable.

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Frequency modulation
In telecommunications and signal
processing, frequency modulation
(FM) is the encoding of information
in a carrier wave by varying the
instantaneous frequency of the wave.
In analog frequency modulation, such
as FM radio broadcasting of an audio
signal representing voice or music, the
instantaneous frequency deviation, the
difference between the frequency of
the carrier and its center frequency, is
proportional to the modulating signal.

Frequency response
Frequency response is the quantitative
measure of the output spectrum of
a system or device in response to a
stimulus, and is used to characterize
the dynamics of the system. It is a
measure of magnitude and phase of
the output as a function of frequency,
in comparison to the input. In simplest
terms, if a sine wave is injected into a
system at a given frequency, a linear
system will respond at that same
frequency with a certain magnitude
and a certain phase angle relative to
the input. Also for a linear system,
doubling the amplitude of the input will
double the amplitude of the output. In
addition, if the system is time-invariant
(so LTI), then the frequency response
also will not vary with time. Thus for
LTI systems, the frequency response can
be seen as applying the system’s transfer
function to a purely imaginary number
argument representing the frequency of
the sinusoidal excitation.

Frequency-shift keying
Frequency-shift keying (FSK) is a
frequency modulation scheme in which
digital information is encoded on a
carrier signal by periodically shifting the
frequency of the carrier between several
discrete frequencies. The technology is
used for communication systems such as
telemetry, weather balloon radiosondes,
caller ID, garage door openers, and
low frequency radio transmission in
the VLF and ELF bands. The simplest
FSK is binary FSK (BFSK), in which the
carrier is shifted between two discrete
frequencies to transmit binary (0s and
1s) information.

Full scale deflection
The full range of motion of an analog
needle of an analog meter, or a
galvanometer.

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Functional neuroimaging
Functional neuroimaging is the use of
neuroimaging technology to measure
an aspect of brain function, often with
a view to understanding the relationship
between activity in certain brain areas
and specific mental functions.
F

Full-wave rectifier
A full-wave rectifier converts the whole
of the input waveform to one of constant
polarity (positive or negative) at its
output. Mathematically, this corresponds
to the absolute value function. Full-wave
rectification converts both polarities of
the input waveform to pulsating DC
(direct current), and yields a higher
average output voltage. Two diodes and
a center tapped transformer, or four
diodes in a bridge configuration and
any AC source (including a transformer
without center tap), are needed. Single
semiconductor diodes, double diodes
with common cathode or common
anode, and four-diode bridges, are
manufactured as single components.

Function generator
A function generator is usually a
piece of electronic test equipment or
software used to generate different
types of electrical waveforms over a
wide range of frequencies. Some of the
most common waveforms produced
by the function generator are the sine
wave , square wave, triangular wave
and sawtooth shapes.

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Fundamental frequency

Fusible-link

The fundamental frequency, often
referred to simply as the fundamental,
is defined as the lowest frequency of
a periodic waveform. In music, the
fundamental is the musical pitch of
a note that is perceived as the lowest
partial present.

A physical link providing electric
continuity across an individual cell in
the memory array of a PROM. With this
link intact the cell,when interrogated,
will display a known logic state.

F

Fuzzy control

Fuse (electrical)
In electronics and electrical engineering,
a fuse is an electrical safety device
that operates to provide overcurrent
protection of an electrical circuit. Its
essential component is a metal wire or
strip that melts when too much current
flows through it, thereby interrupting
the current. It is a sacrificial device; once
a fuse has operated it is an open circuit,
and it must be replaced or rewired,
depending on type.

A fuzzy control system is a control system
based on fuzzy logic—a mathematical
system that analyzes analog input values
in terms of logical variables that take
on continuous values between 0 and 1,
in contrast to classical or digital logic,
which operates on discrete values of
either 1 or 0 (true or false, respectively).

Fuzzy logic
Fuzzy logic is an approach to computing
based on “degrees of truth” rather than
the usual “true or false” (1 or 0) Boolean
logic on which the modern computer
is based. The idea of fuzzy logic was
first advanced by Dr. Lotfi Zadeh of the
University of California at Berkeley in
the 1960s.

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FWHM

F

In a distribution, full width at half
maximum is the difference between the
two values of the independent variable
at which the dependent variable is equal
to half of its maximum value. In other
words, it is the width of a spectrum
curve measured between those points on
the y-axis which are half the maximum
amplitude.

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Gg
GaAs
Gallium arsenide: A semiconductor
material used for optoelectronic
products such as LEDs, and for highspeed electronic devices.

Gain Block
A component that provides amplification,
which normally contains additional
circuitry in addition to a simple
amplifier.

GaAs MESFET
A Gallium Arsenide (GaAs) MetalSemiconductor Field-Effect-Transistor
(MESFET) is a transistor built with
gallium arsenide semiconductor
material. The conducting channel is built
using a metal-semiconductor (Schottky)
junction.

GaAsP
Gallium Arsenide Phosphide (or, Gallium
Arsenic Phosphide): A semiconductor
material used for optoelectronics,
including LEDs and photodiodes.

Gain

Gain compression
Gain compression is a reduction in
“differential” or “slope” gain caused by
nonlinearity of the transfer function of
the amplifying device. This nonlinearity
may be caused by heat due to power
dissipation or by overdriving the active
device beyond its linear region. It is
a large-signal phenomenon of circuits.

Any increase in the strength of a signal.
The ratio of output current, voltage,
or power to input current, voltage, or
power, respectively. The ratio of the
magnitude of an output signal compared
to the input signal.
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usually expressed in LSB or as a percent
of full-scale range (%FSR), and it can
be calibrated out with hardware or in
software. Gain error is the full-scale
error minus the offset error.

G

Gain control
The purpose of a gain control is to tune
the amp’s input stage to accept the head
unit’s voltage level. Think about it like
a cellphone conversation. Your job is to
listen to the person on the other end.
With phone turned down too low, you
can’t hear the other person over the
background noise around you.

Gain margin
Gain Error

Gain margin is defined as the amount
of change in open-loop gain needed to
make a closed-loop system unstable. The
gain margin is the difference between 0
dB and the gain at the phase cross-over
frequency that gives a phase of −180°.

The gain error of a data converter
indicates how well the slope of an actual
transfer function matches the slope of
the ideal transfer function.
Gain error is usually expressed in
LSB or as a percent of full-scale range.
Gain error can be calibrated out with
hardware or in software. Gain error
is the full-scale error minus the offset
error.

Galactic noise
It has been called “noise” as it can
actually be heard in earphones.

The gain error of an ADC or DAC
indicates how well the slope of an actual
transfer function matches the slope of
the ideal transfer function. Gain error is
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G

Gain scheduling
In control theory, gain scheduling is
an approach to control of non-linear
systems that uses a family of linear
controllers, each of which provides
satisfactory control for a different
operating point of the system.
One or more observable variables,
called the scheduling variables, are
used to determine what operating
region the system is currently in
and to enable the appropriate linear
controller. For example, in an aircraft
flight control system, the altitude and
Mach number might be the scheduling
variables, with different linear controller
parameters available (and automatically
plugged into the controller) for various
combinations of these two variables.

Galvanic corrosion
Galvanic corrosion (also called bimetallic
corrosion) is an electrochemical
process in which one metal corrodes
preferentially when it is in electrical
contact with another, in the presence
of an electrolyte. A similar galvanic
reaction is exploited in primary cells
to generate a useful electrical voltage
to power portable devices.

Gain-Bandwidth Product
The number that results when the gain of
a circuit is multiplied by the bandwidth
of that circuit. For an operational
amplifier, the gain-bandwidth product
for one configuration will always
equal the gain-bandwidth product for
any other configuration of the same
amplifier.

Galvanic Isolation
The separation in movement of chargecarrying particles from one section
to another. A current moving in one
section of a circuit does not flow in
another section of the circuit. Isolation
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Gamma

between the ground reference of two
power systems such that the potential
difference between the two ground
references, up to some maximum
voltage, would not cause damage or
interference to normal operations.

The application of a function that
transforms brightness or luminance
values. Gamma functions are usually
nonlinear but monotonic and designed
to affect the highlights (whitest values),
midtones (grayscale), and shadows
(dark areas) separately.
Most commonly applied to make a
light-emitting device, such as a display,
match the human eye’s brightness curve.
In other terms: A gamma correction
function can be used to alter the
luminance (light intensity) of a display
such that its brightness (the humanperceived values) looks correct.

G

Ganged Tuning
Galvanometer

A variable capacitor connected in parallel
with another variable capacitor so that
as one is varied they both change by
the same degree. The graphic represent
the schematic symbol for a GangedCapacitor.

A galvanometer is an electromechanical
instrument for detecting and indicating
electric current. A galvanometer works
as an actuator, by producing a rotary
deflection (of a “pointer”), in response
to electric current flowing through a
coil in a constant magnetic field. Early
galvanometers were not calibrated, but
their later developments were used as
measuring instruments, called ammeters,
to measure the current flowing through
an electric circuit.

Gapped Clock
A periodic clock stream which is missing
clock pulses at arbitrary intervals for
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arbitrary lengths of time. A clock signal
which has had one or more clock pulses
removed from the series.

Garble

the tube. When sufficient voltage is
applied to the tube, ionization of the
gas molecules occurs and is responsible
for the current passing through the tube
during operation.

An error in transmission or reception,
that results in incorrect or un-decryptable
information.
G

Gas Gauge
Gas Discharge Tube
A gas filled tube that illuminates by
ionizing the gas within the tube with
an applied voltage.

Gas Filled Tube
Gas Tube. A two-electrode vacuum tube
with a cathode and plate. The evacuated
tube contains a small amount of gas,
such as neon, which is sealed inside

A feature or device that measures the
accumulated energy added to and
removed from a battery, allowing
accurate estimates of battery charge
level.

Gasket
A preformed shapeable component that
is placed between two adjoining parts to
prevent electromagnetic radiation into
or escaping from an enclosure or system.

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G

Gate

Gated-Beam Detector

As applied to logic circuitry, one of
several different types of electronic
devices that will provide a particular
output when specified input conditions
are satisfied. Gate; as in AND Gate, OR
Gate, NOR Gate, NAND Gate or Inverter
[shown to the right]. Also, a circuit in
which a signal switches another signal
on or off. The electrode associated with
the region in which the electric field
due to the control voltage is effective

An FM demodulator that uses a special
gated-beam tube to limit, detect, and
amplify the received FM signal. Also
known as a quadrature detector.

Gating
The process of selecting those portions
of a wave that exist during one or more
selected time intervals or that have
magnitudes between selected limits. Also,
the application of a specific waveform
to perform electronic switching.

Gauss’s law
In physics, Gauss’s law, also known as
Gauss’s flux theorem, is a law relating
the distribution of electric charge to
the resulting electric field. The surface
under consideration may be a closed one
enclosing a volume such as a spherical
surface.

Gate Pulse
A signal pulse use to gate or allow
another signal through a circuit.

Gate Turn-off Thyristor.
[GTO]
A Thyristor that may be turned on or
off by a signal applied to the gate, as
opposed to only being turned on with
a normal thyristor. Also refer to GTO
Thyristor Manufacturers for a list of
vendors.

Gauss-Seidel method
The Gauss–Seidel method, also known as
the Liebmann method or the method of
successive displacement, is an iterative
method used to solve a linear system of
equations. It is named after the German
mathematicians Carl Friedrich Gauss
and Philipp Ludwig von Seidel, and is
similar to the Jacobi method. Though

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it can be applied to any matrix with
non-zero elements on the diagonals,
convergence is only guaranteed if the
matrix is either diagonally dominant, or
symmetric and positive definite.

GBIC
Gigabit Interface Converter: A removable
transceiver module permitting FibreChannel and Gigabit-Ethernet physicallayer transport.

General Purpose Interface
Bus
General Purpose Interface Bus: A
standard bus for controlling electronic
instruments with a computer. Also
called IEEE-488 bus because it is defined
by ANSI/IEEE Standards 488-1978,
and 488.2-1987. Also called HP-IB, a
trademarked term of Hewlett-Packard,
which invented the protocol.

Generator

General Packet Radio
Service
General Packet Radio Service: A radio
technology for GSM networks that adds
packet-switching protocols and shorter
set-up time for ISP connections; it offers
the possibility to charge by amount of
data sent rather than connect time.

A generator in electrical circuit theory
is one of two ideal elements: an ideal
voltage source, or an ideal current
source. These are two of the fundamental
elements in circuit theory. Real electrical
generators are most commonly modelled
as a non-ideal source consisting of a
combination of an ideal source and a
resistor. Voltage generators are modelled
as an ideal voltage source in series
with a resistor. Current generators are
modelled as an ideal current source in
parallel with a resistor. The resistor is
referred to as the internal resistance
of the source. Real world equipment
may not perfectly follow these models,
especially at extremes of loading (both
high and low) but for most purposes
they suffice.

General Purpose I-O
General Purpose I/O: A flexible parallel
interface that allows a variety of custom
connections.

Geothermal power
Geothermal power is power generated
by geothermal energy. Technologies in
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GFSK

use include dry steam power stations,
flash steam power stations and binary
cycle power stations. Geothermal
electricity generation is currently used in
24 countries, while geothermal heating
is in use in 70 countries.

Gaussian frequency-shift keying: A
type of FSK modulation which uses
a Gaussian filter to shape the pulses
before they are modulated. This reduces
the spectral bandwidth and out-of-band
spectrum, to meet adjacent-channel
power rejection requirements. Bluetooth
uses GFSK.

Germanium
G

Germanium is a chemical element with
symbol Ge and atomic number 32. It is a
lustrous, hard, grayish-white metalloid
in the carbon group, chemically similar to
its group neighbors tin and silicon. Pure
germanium is a semiconductor with an
appearance similar to elemental silicon.
Like silicon, germanium naturally reacts
and forms complexes with oxygen in
nature.
A grayish-white metal having
semiconductor properties, similar to tin.
Many transistors once used Germanium
as the semiconductor material [example
Germanium diodes; 1N270, 1N276,
1N277, 1N3287 and Germanium
transistors 2N384, 2N539, 2N1120].

Gigabit
The gigabit is a multiple of the unit
bit for digital information or computer
storage. The prefix giga(symbol G) is
defined in the International System of
Units (SI) as a multiplier of 109 (1 billion,
short scale), and therefore
1 gigabit = 109bits = 1000000000bits.
The gigabit has the unit symbol
Gbit or Gb.

Glitch
General term used to describe an
undesirable, momentary pulse or
unexpected input or output.

Germanium Photodiode

Glitch Immunity

A germanium-based PN- or PIN-junction
photodiode.

A term used in microprocessor
supervisory circuit datasheets to describe
the maximum magnitude and duration
of a negative-going VCC supply-voltage
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pulse without causing the reset output
to assert.

Global Positioning System
Global Positioning System: A satellitebased navigation system in which two
or more signals, received from satellites,
are used to determine the receiver’s
position on the globe.
The Global Positioning System
(GPS), originally Navstar GPS, is a
space-based radionavigation system
owned by the United States government
and operated by the United States Air
Force. It is a global navigation satellite
system that provides geolocation and
time information to a GPS receiver
anywhere on or near the Earth where
there is an unobstructed line of sight
to four or more GPS satellites.

GMSK
Gaussian minimum shift keying (GMSK)
is a form of frequency shift keying
(FSK) used in GSM systems. The tone
frequencies are separated by exactly
half the bit rate. It has high spectral
efficiency.

GMSL
Gigabit Multimedia Serial Link. This
is a Maxim-specific category name
for a range of products that serialize,
desterilize, and buffer high-speed digital
data streams for communications over
short distances.

G

Gold
Gold is a chemical element with symbol
Au (from Latin: aurum) and atomic
number 79. In its purest form, it is a
bright, slightly reddish yellow, dense,
soft, malleable, and ductile metal.
Chemically, gold is a transition metal
and a group 11 element. It is one of the
least reactive chemical elements and is
solid under standard conditions. Gold
often occurs in free elemental (native)
form, as nuggets or grains, in rocks,
in veins, and in alluvial deposits. It
occurs in a solid solution series with
the native element silver (as electrum)
and also naturally alloyed with copper
and palladium. Less commonly, it occurs
in minerals as gold compounds, often
with tellurium (gold tellurides).

Governor (device)
A governor, or speed limiter or
controller, is a device used to measure
and regulate the speed of a machine,
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such as an engine. A classic example
is the centrifugal governor, also known
as the Watt or fly-ball governor on a
reciprocating steam engine, which uses
the effect of centrifugal force on rotating
weights driven by the machine output
shaft to regulate its speed by altering
the input flow of steam.

minimum of a function using gradient
descent, one takes steps proportional to
the negative of the gradient (or of the
approximate gradient) of the function at
the current point. If instead one takes
steps proportional to the positive of
the gradient, one approaches a local
maximum of that function; the procedure
is then known as gradient ascent.
Gradient descent is also known as
steepest descent. However, gradient
descent should not be confused with
the method of steepest descent for
approximating integrals.

G

Gravitational force
The gravitational force is a force that
attracts any two objects in the universe,
whether they have equal masses or not.
Furthermore, Newton’s Universal Law
of Gravitation states that everything,
including you, pulls every other object
in the universe. The unit of gravitational
force is Newtons, denoted as N.

GPIB
General Purpose Interface Bus: A
standard bus for controlling electronic
instruments with a computer. Also
called IEEE-488 bus because it is defined
by ANSI/IEEE Standards 488-1978,
and 488.2-1987. Also called HP-IB, a
trademarked term of Hewlett-Packard,
which invented the protocol.

Grid energy storage
Grid energy storage (also called largescale energy storage) is a collection of
methods used to store electrical energy
on a large scale within an electrical power
grid. Electrical energy is stored during
times when production (especially
from intermittent power plants such
as renewable electricity sources such as
wind power, tidal power, solar power)
exceeds consumption, and returned to

Gradient descent
Gradient descent is a first-order iterative
optimization algorithm for finding the
minimum of a function. To find a local
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the grid when production falls below
consumption.

Grid-tie inverter
A grid-tie inverter converts direct current
(DC) into an alternating current (AC)
suitable for injecting into an electrical
power grid, normally 120V RMS at 60Hz
or 240V RMS at 50 Hz. Grid-tie inverters
are used between local electrical power
generators: solar panel, wind turbine,
hydro-electric, and the grid.
In order to inject electrical power
efficiently and safely into the grid, gridtie inverters must accurately match the
voltage and phase of the grid sine wave
AC waveform.
Some electricity companies will pay
for electrical power that is injected into
the grid.

Ground (electricity)
In electrical engineering, ground
or earth is the reference point in an
electrical circuit from which voltages
are measured, a common return path
for electric current, or a direct physical
connection to the Earth.
Electrical circuits may be connected
to ground (earth) for several reasons.
In mains powered equipment, exposed
metal parts are connected to ground
so that if, due to any fault conditions,
a “Line” supply voltage connection
occurs to any such conductive parts,
the current flow will then be such that
any protective equipment installed for
either overload or “leakage” protection
will operate and disconnect the “Line”
voltage. This is done to prevent harm
resulting to the user from coming in
contact with any such dangerous voltage
in a situation where the user may, at the
same time, also come in contact with
an object at ground/earth potential. In
electrical power distribution systems,
a Protective Earth (PE) conductor is an
essential part of the safety provided by
the earthing system.

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Ground and neutral

G

have Angers (Tramway d’Angers) and
Dubai (Al Sufouh Tram).

As the neutral point of an electrical
supply system is often connected to
earth ground, ground and neutral
are closely related. Under certain
conditions, a conductor used to connect
to a system neutral is also used for
grounding (earthing) of equipment
and structures. Current carried on a
grounding conductor can result in
objectionable or dangerous voltages
appearing on equipment enclosures, so
the installation of grounding conductors
and neutral conductors is carefully
defined in electrical regulations. Where
a neutral conductor is used also to
connect equipment enclosures to earth,
care must be taken that the neutral
conductor never rises to a high voltage
with respect to local ground.

Growler (electrical device)
A growler is an electrical device used
for testing insulation of a motor for
shorted coils. A growler consists of a
coil of wire wrapped around an iron
core and connected to a source of AC
current. When placed on the armature or
stator core of a motor the growler acts
as the primary of a transformer and the
armature coils act as the secondary. A
“feeler”, a thin strip of steel (hacksaw
blade) can be used as the short detector.

GSM900
Ground-level power supply

GSM network operating in the 900MHz
band, as used by BT Cellnet and
Vodafone in the UK, and by more
than one hundred countries around
the world.

Ground-level power supply, also
known as surface current collection and
Alimentation par le Sol (APS, which
literally means feeding via the ground),
is a modern method of third-rail electrical
pick-up for street trams. It was invented
for the Bordeaux tramway (Tramway de
Bordeaux), which was constructed from
2000 and opened in 2003. Until 2011,
this was the only place it was used,
with proposals to install it elsewhere.
Reims has adopted this technology for
its new Reims Tramway (Tramway de
Reims), which was opened in 2011, as

GT
Transfer refers to the amount of data
transferred across a digital interface,
exclusive of any extra bits used to
encode the data.
The number of data transfers is less
than the number of bits transmitted
when encoded data has more bits
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than the raw data. As an example, a
PCIe serial bus uses 10 bits to encode
eight data bits. (Extra bit space may be
used to encode a clock, error-detection
redundancy, etc.)

microwaves, in applications such as
radar speed guns, microwave relay data
link transmitters, and automatic door
openers.

Data rates are commonly expressed
in transfers per second, gigatransfers
per second (GT/s) and megatransfers
per second (MT/s).

G

Gyrotron

GUI
The graphical user interface, is a type
of user interface that allows users to
interact with electronic devices through
graphical icons and visual indicators
such as secondary notation, instead
of text-based user interfaces, typed
command labels or text navigation.

A gyrotron is a high-power linearbeam vacuum tube which generates
millimeter-wave electromagnetic waves
by the cyclotron resonance of electrons
in a strong magnetic field. Output
frequencies range from about 20 to
527 GHz, covering wavelengths from
microwave to the edge of the terahertz
gap. Typical output powers range from
tens of kilowatts to 1–2 megawatts.
Gyrotrons can be designed for pulsed
or continuous operation.

Gunn diode
A Gunn diode, also known as a
transferred electron device (TED), is a
form of diode, a two-terminal passive
semiconductor electronic component,
with negative resistance, used in highfrequency electronics. It is based on
the “Gunn effect” discovered in 1962
by physicist J. B. Gunn. Its largest use
is in electronic oscillators to generate

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Hh

Half-wave dipole
The half wave dipole is the most popular
version of the dipole antenna or aerial.
As the name implies, the half wave
dipole is a half wavelength long. This
is the shortest resonant length that can
be used for a resonant dipole. It also
has a very convenient radiation pattern.

Halation
The spreading of light beyond its proper
boundaries to form a fog round the
edges of a bright image in a photograph
or on a television screen.

H

Half Adder
A circuit that adds two 1-bit binary
numbers and output a sum bit and a
carry bit, but does not have a provision
to accept a carry input from a previous
adder stage. Two Half Adders can be
combined to form a Full Adder.

Half-power beamwidth

Half-Duplex

The Half Power Beamwidth (HPBW)
is the angular separation in which the
magnitude of the radiation pattern
decrease by 50% (or -3 dB) from the
peak of the main beam.

Data flow in either direction, but not in
both directions at the same time. There
are a number of interface buses that
only allow Half-Duplex operation, while
some bus networks just add a redundant
path in the opposite direction to allow
communication in either direction at the
same time. Operation in both directions
at the same time is called Full-Duplex.
An Abbreviation for half duplex is HDX.

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Half-Flash
An ADC architecture which uses a bank
of comparators first to digitize the upper
half bits, then uses a digital-to-analog
converter (DAC) to subtract that voltage
from the input, and then digitizes what
remains of the input signal to get the
lower half bits. Also see application note
748, “The ABCs of ADCs.”

Half-Power Point
A point on a waveform or radar beam
that corresponds to half the power of
the maximum power point.

H

Half-Wave Voltage
Doubler
Two half-wave voltage rectifier circuits
connected to double the input voltage.
Read more on Voltage Multiplier
Circuits. A voltage doubler circuit that
only operates on half of the input cycle.

Half-Wave Rectifier
A rectifier using only one-half of each
cycle to change ac to pulsating dc. The
direction of the diode or the winding
of the transformer selects the polarity
of the output across the load. Resistor
Rs is not required but is used to limit
the current through the diode. Refer to
the Half-Wave Rectifier Circuit detail.

Hall Effect
An electric field that is produced when
a current carrying conductor is placed
in a magnetic field whose direction is
perpendicular to both the direction of
the current and the magnetic field.
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Hall effect sensor
A Hall effect sensor is a transducer that
varies its output voltage in response
to a magnetic field. Hall effect sensors
are used for proximity switching,
positioning, speed detection, and current
sensing applications.

H

In a Hall effect sensor a thin strip
of metal has a current applied along
it, in the presence of a magnetic field
the electrons are deflected towards one
edge of the metal strip, producing a
voltage gradient across the short-side
of the strip (perpendicular to the feed
current). Inductive sensors are just a coil
of wire, in the presence of a changing
magnetic field a current will be induced
in the coil, producing a voltage at its
output. Hall effect sensors have the
advantage that they can detect static
(non-changing) magnetic fields.

Hamming Weight
The number of non-zero symbols in a
symbol sequence.

Handover
Switching an on-going call to a different
channel or cell in a wireless cellular
network. Also known as “handoff.”

Halt
A command that stops the transfer of
data on a bus, or stops the executions
of commands by a processor.

Hamming Code
An error-detecting and error-correcting
binary code, used in data transmission
that can detect all single- and double-bit
errors and correct all single-bit errors.
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Hand-Shake
The interchange of signals between
a ‘talker’ and a ‘listener’ to exchange
data on a bus. During a Handshake
a listener [slave] indicates ready for
data, a talker [master] indicates data
ready, and the slave then indicates
data received. Read more on the
Handshaking Protocol. Handshaking
is normally used when interfacing
to peripherals that communicate at
different speeds, or transfer data at
different rates. Handshaking allows the
devices to communicate at the same
rate, as determined by the speed of the
mutual handshake.

Hard Disk
A flat, circular, rigid plate with a
magnetizable surface on one or both
sides used to store data. Also called a
Hard Disk Drive [HDD]. Note: A hard
disk is distinguished from a diskette
[floppy Disk] by virtue of the fact that
it is rigid and not considered removable.
Manufacturers of Hard Disk Drives.

Hardware
The physical equipment or component
used to perform some function, in
contrast to software.

Hardware Interrupt
An interrupt signal received from a
component external to the processor
operating on the interrupt. A signal to
the processor that a peripheral requires
attention.

Harmonic
Hard-Tube
A high-vacuum electron tube modulator
that uses a driver for pulse forming. See
Vacuum Tube.

A harmonic is any member of the
harmonic series, a divergent infinite
series. Its name derives from the
concept of overtones, or harmonics in
musical instruments: the wavelengths
of the overtones of a vibrating string
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of distortion (like crossover distortion)
are more audible than others (like soft
clipping) even if the THD measurements
are identical. Harmonic distortion in
radio frequency applications is rarely
expressed as THD.

or a column of air (as with a tuba) are
derived from the string’s (or air column’s)
fundamental wavelength. Every term of
the series (i.e., the higher harmonics)
after the first is the “harmonic mean”
of the neighboring terms. The phrase
“harmonic mean” likewise derives from
music.

H

Harness
An assembly of wires or cables, or
wires and cables arranged so it may
be installed or removed as a unit in the
same electronic or electrical equipment.
One or more insulated wires or cables,
with or without helical twist; with
or without common covering, jacket,
or braid; with or without breakouts;
assembled with two or more electrical
termination devices; and so arranged
that as a unit it can be assembled and
handled as one assembly. Also refer to
Cable Harness Discussion for additional
information.

Harmonic distortion
The presence of frequencies in the
output of a device that are not present
in the input signal, and are multiples
of components of the input signal.
Clipping is a common cause but
other nonlinearities can also introduce
harmonics.
Harmonic distortion adds overtones
that are whole number multiples of a
sound wave’s frequencies. Nonlinearities
that give rise to amplitude distortion in
audio systems are most often measured
in terms of the harmonics (overtones)
added to a pure sinewave fed to the
system. Harmonic distortion may be
expressed in terms of the relative
strength of individual components, in
decibels, or the root mean square of all
harmonic components: Total harmonic
distortion (THD), as a percentage. The
level at which harmonic distortion
becomes audible depends on the exact
nature of the distortion. Different types
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HART
Highway Addressable Remote
Transducer (HART) communication is
a commonly used mode of transmission
for digital signals that are superimposed
on the analog signal of a 4–20mA current
loop.
The HART protocol is based on the
phase continuous frequency shift keying
(FSK) technique. Bit 0 is modulated to
a 2200Hz sinusoidal signal, and bit 1
is modulated to a 1200Hz sinusoidal
signal with a baud rate of 1200bps.
These two frequencies can easily be
superimposed on the analog currentloop signal, which is in the range of
DC to 10Hz, without affecting either
signal. This unique nature of the HART
protocol enables simultaneous analog
and digital communication on the same
wire.

HAST
Highly accelerated stress test; highly
accelerated steam and temperature.

Hay Bridge
An AC bridge that uses capacitors and
resistors to determine the value of an
unknown inductor.

Hartley Oscillator

HB LED

An oscillator that uses two series
connected inductors in parallel [a tapped
coil or split coil] with a capacitor. The
feedback point for the Hartley oscillator
is between the two inductors as shown
in the diagram. The oscillating frequency
is determined by the LC circuit.

High-Brightness LEDs are any of
a new generation of LEDs bright
enough for illumination applications
such as automotive interior, exterior,
and display; room and architectural
illumination; task and general lighting;
projection display; display backlights;
and signage.

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semiconductor materials for the
emitter and base regions, creating a
heterojunction. The HBT improves on
the BJT in that it can handle signals
of very high frequencies, up to several
hundred GHz. It is commonly used
in modern ultrafast circuits, mostly
radio-frequency (RF) systems, and
in applications requiring a high
power efficiency, such as RF power
amplifiers in cellular phones. The idea
of employing a heterojunction is as old
as the conventional BJT, dating back to
a patent from 1951.

H-Bridge
H

An H bridge is an electronic circuit that
enables a voltage to be applied across a
load in opposite direction. These circuits
are often used in robotics and other
applications to allow DC motors to run
forwards or backwards.
Most DC-to-AC converters (power
inverters), most AC/AC converters, the
DC-to-DC push–pull converter, most
motor controllers, and many other kinds
of power electronics use H bridges. In
particular, a bipolar stepper motor is
almost invariably driven by a motor
controller containing two H bridges.

HDLC
High-level Data Link Control is a
group of protocols for transmitting
[synchronous] data Packets between
Point-to-Point nodes. Data is organized
into a frame in HDLC. HDLC protocol
resides with Layer 2 of the OSI model,
the data link layer.

HDSL
High bit-rate Digital Subscriber Line
is the oldest of the DSL technologies,
it continues to be used by telephone
companies deploying T1 lines at
1.5Mbps and requires two twisted pairs.

HBT
The heterojunction bipolar transistor
(HBT) is a type of bipolar junction
transistor (BJT) which uses differing
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HDTV
High-definition television (HDTV) is a
television system providing an image
resolution that is of substantially
higher resolution than that of standarddefinition television. HDTV is the
current standard video format used in
most broadcasts: terrestrial broadcast
television, cable television, satellite
television, Blu-rays, and streaming
video.

Headphone
Headphones (or head-phones in the
early days of telephony and radio) are
a pair of small loudspeaker drivers worn
on or around the head over a user’s ears.
They are electroacoustic transducers,
which convert an electrical signal to a
corresponding sound. Headphones let
a single user listen to an audio source
privately, in contrast to a loudspeaker,
which emits sound into the open air for
anyone nearby to hear. Headphones are

also known as earspeakers, earphones
or, colloquially, cans. Circumaural and
supra-aural headphones use a band over
the top of the head to hold the speakers
in place. The other type, known as
earbuds or earpieces consist of individual
units that plug into the user’s ear canal.
In the context of telecommunication, a
headset is a combination of headphone
and microphone. Headphones connect
to a signal source such as an audio
amplifier, radio, CD player, portable
media player, mobile phone, video
game console, or electronic musical
instrument, either directly using a cord,
or using wireless technology such as
bluetooth, DECT or FM radio. The first
headphones were developed in the
late 19th century for use by telephone
operators, to keep their hands free.
Initially the audio quality was mediocre
and a step forward was the invention
of high fidelity headphones.

Heat Sink
A heat sink (also commonly spelled
heatsink) is a passive heat exchanger
that transfers the heat generated by an
electronic or a mechanical device to
a fluid medium, often air or a liquid
coolant, where it is dissipated away
from the device, thereby allowing
regulation of the device’s temperature at
optimal levels. In computers, heat sinks
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are used to cool central processing units
or graphics processors. Heat sinks are
used with high-power semiconductor
devices such as power transistors and
optoelectronics such as lasers and light
emitting diodes (LEDs), where the heat
dissipation ability of the component
itself is insufficient to moderate its
temperature.

and humidity), energy efficiency, and
air quality.

H

Helmholtz coil
A Helmholtz coil is a device for
producing a region of nearly uniform
magnetic field, named after the German
physicist Hermann von Helmholtz. It
consists of two solenoid electromagnets
on the same axis. Besides creating
magnetic fields, Helmholtz coils are also
used in scientific apparatus to cancel
external magnetic fields, such as the
Earth’s magnetic field.

Heat transfer
Heat transfer is a discipline of thermal
engineering that concerns the generation,
use, conversion, and exchange of
thermal energy (heat) between physical
systems. Heat transfer is classified into
various mechanisms, such as thermal
conduction, thermal convection, thermal
radiation, and transfer of energy by
phase changes. Engineers also consider
the transfer of mass of differing chemical
species, either cold or hot, to achieve
heat transfer. While these mechanisms
have distinct characteristics, they often
occur simultaneously in the same
system.

Heating, Ventilation, and
Air Conditioning

HEMT

Heating, Ventilation, and Air
Conditioning is the industry term for
the systems and technology responsible
for the heating, ventilation, and air
conditioning in buildings. HVAC
systems regulate comfort (temperature

A High-electron-mobility transistor
(HEMT), also known as heterostructure
FET (HFET) or modulation-doped FET
(MODFET), is a field-effect transistor
incorporating a junction between two
materials with different band gaps (i.e.
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a heterojunction) as the channel instead
of a doped region (as is generally
the case for MOSFET). A commonly
used material combination is GaAs
with AlGaAs, though there is wide
variation, dependent on the application
of the device. Devices incorporating
more indium generally show better
high-frequency performance, while in
recent years, gallium nitride HEMTs
have attracted attention due to their
high-power performance. Like other
FETs, HEMTs are used in integrated
circuits as digital on-off switches. FETs
can also be used as amplifiers for large
amounts of current using a small voltage
as a control signal. Both of these uses
are made possible by the FET’s unique
current-voltage characteristics. HEMT
transistors are able to operate at higher
frequencies than ordinary transistors,
up to millimeter wave frequencies, and
are used in high-frequency products
such as cell phones, satellite television
receivers, voltage converters, and radar
equipment. They are widely used
in satellite receivers, in low power
amplifiers and in the defense industry.

Henry (unit)
The henry (symbol: H) is the SI derived
unit of electrical inductance. The unit
is named after Joseph Henry (1797–
1878), the American scientist who
discovered electromagnetic induction
independently of and at about the same
time as Michael Faraday (1791–1867) in
England.

H

Hertz
The hertz (symbol: Hz) is the derived
unit of frequency in the International
System of Units (SI) and is defined
as one cycle per second.[1] It is named
for Heinrich Rudolf Hertz, the first
person to provide conclusive proof
of the existence of electromagnetic
waves. Hertz are commonly expressed
in multiples: kilohertz (103 Hz, kHz),
megahertz (106 Hz, MHz), gigahertz (109
Hz, GHz), and terahertz (1012 Hz, THz).

Heterostructure
A heterojunction is the interface that
occurs between two layers or regions
of dissimilar crystalline semiconductors.
These semiconducting materials have
unequal band gaps as opposed to a
homojunction. It is often advantageous
to engineer the electronic energy bands
in many solid-state device applications,
including semiconductor lasers, solar
cells and transistors (“heterotransistors”)
to name a few. The combination of
multiple heterojunctions together in
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H

a device is called a heterostructure,
although the two terms are commonly
used interchangeably. The requirement
that each material be a semiconductor
with unequal band gaps is somewhat
loose, especially on small length
scales, where electronic properties
depend on spatial properties. A more
modern definition of heterojunction is
the interface between any two solidstate materials, including crystalline
and amorphous structures of metallic,
insulating, fast ion conductor and
semiconducting materials.

Hi-Fi
High fidelity (often shortened to hifi or hifi) reproduction is a term used
by home stereo listeners, audiophiles
and home audio enthusiasts to refer
to high-quality reproduction of sound
to distinguish it from the lower quality
sound produced by inexpensive audio
equipment, or the inferior quality of
sound reproduction that can be heard
in recordings made until the late 1940s.
Ideally, high-fidelity equipment has
inaudible noise and distortion, and a flat
(neutral, uncolored) frequency response
within the intended frequency range.

HF

High impedance

H i g h freq u en cy (H F ) i s an
electromagnetic frequency defined by
the International Telecommunications
Union (ITU) for radar and radio
communications. It operates in a
range of three to thirty MHz and as
the wavelengths spread over ten to
one hundred meters, it is also known
as decameter wave and designated
as band 7. High frequency is highly
popular among amateur radio, military
and government communications,
radar communications and global
maritime distress and safety system
communications.

Hi-Z (or High-Z or high impedance)
refers to an output signal state in
which the signal is not being driven.
The signal is left open, so that another
output pin (e.g. elsewhere on a bus)
can drive the signal or the signal level
can be determined by a passive device
(typically, a pull-up resistor).

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High voltage
The term high voltage usually means
electrical energy at voltages high enough
to inflict harm on living organisms.
Equipment and conductors that carry
high voltage warrant particular safety
requirements and procedures. In certain
industries, high voltage means voltage
above a particular threshold (see below).
High voltage is used in electrical power
distribution, in cathode ray tubes, to
generate X-rays and particle beams,
to demonstrate arcing, for ignition,
in photomultiplier tubes, and in high
power amplifier vacuum tubes and other
industrial and scientific applications.

used in conjunction with a low-pass
filter to produce a bandpass filter.

H

High-Side
An element connected between the
supply and the load. High-side current
sensing applications measure current
by looking at the voltage drop across
a resistor placed between the supply
and the load.

High-pass filter

High-Speed Packet Access

A high-pass filter (HPF) is an electronic
filter that passes signals with a frequency
higher than a certain cutoff frequency
and attenuates signals with frequencies
lower than the cutoff frequency. The
amount of attenuation for each frequency
depends on the filter design. A highpass filter is usually modeled as a linear
time-invariant system. It is sometimes
called a low-cut filter or bass-cut filter.
High-pass filters have many uses, such
as blocking DC from circuitry sensitive
to non-zero average voltages or radio
frequency devices. They can also be

High-Speed Packet Access (HSPA) is a
collection of radio interface standards
for wireless and cellular handsets or
datacards that increase the datarate and
improve the traffic handling of existing
UMTS standards.

High-voltage cable
A high-voltage cable (HV cable) is a cable
used for electric power transmission at
high voltage. A cable includes a conductor
and insulation, and is suitable for being
run underground or underwater. This

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H

is in contrast to an overhead line,
which does not have insulation. Highvoltage cables of differing types have a
variety of applications in instruments,
ignition systems, and AC and DC
power transmission. In all applications,
the insulation of the cable must not
deteriorate due to the high-voltage stress,
ozone produced by electric discharges
in air, or tracking. The cable system
must prevent contact of the high-voltage
conductor with other objects or persons,
and must contain and control leakage
current. Cable joints and terminals must
be designed to control the high-voltage
stress to prevent breakdown of the
insulation. Often a high-voltage cable
will have a metallic shield layer over
the insulation, connected to the ground
and designed to equalize the dielectric
stress on the insulation layer.

and discharge the cable capacitance
each cycle. For shorter distances, the
higher cost of DC conversion equipment
compared to an AC system may still be
justified, due to other benefits of direct
current links.

High-voltage switchgear
In an electric power system, switchgear is
the combination of electrical disconnect
switches, fuses or circuit breakers used
to control, protect and isolate electrical
equipment. Switchgear is used both to
de-energize equipment to allow work to
be done and to clear faults downstream.
This type of equipment is directly linked
to the reliability of the electricity supply.

High-voltage direct current
A high-voltage, direct current (HVDC)
electric power transmission system (also
called a power super highway or an
electrical super highway) uses direct
current for the bulk transmission of
electrical power, in contrast with the
more common alternating current (AC)
systems. For long-distance transmission,
HVDC systems may be less expensive
and suffer lower electrical losses. For
underwater power cables, HVDC avoids
the heavy currents required to charge

Home appliance
Home appliances are electrical/
mechanical machines which accomplish

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some household functions, such as
cooking, cleaning, or food preservation.

Home RF
Trademarked name for Home Radio
Frequency, a networking technology
which uses antennae and transmitters
to provide wireless home networking
via transmitted radio signals.

HomePlug

generator, disk dynamo, or Faraday
disc. The voltage is typically low, on
the order of a few volts in the case
of small demonstration models, but
large research generators can produce
hundreds of volts, and some systems
have multiple generators in series to
produce an even larger voltage. They
are unusual in that they can source
tremendous electric current, some more
than a million amperes, because the
homopolar generator can be made to
have very low internal resistance.
H

HomePlug (Powerline) is an industrystandard method for transmitting data
via the power lines. It can transmit audio,
video, control signals, etc. HomePlug is
a trademark of the HomePlug Powerline
Alliance; Powerline is the generic term
for the method.

Homopolar motor

Homopolar generator
A homopolar generator is a DC electrical
generator comprising an electrically
conductive disc or cylinder rotating in
a plane perpendicular to a uniform static
magnetic field. A potential difference is
created between the center of the disc
and the rim (or ends of the cylinder)
with an electrical polarity that depends
on the direction of rotation and the
orientation of the field. It is also
known as a unipolar generator, acyclic

A homopolar motor is a direct current
electric motor with two magnetic poles,
the conductors of which always cut
unidirectional lines of magnetic flux
by rotating a conductor around a fixed
axis so that the conductor is at right
angles to a static magnetic field. The
resulting EMF (Electromotive Force)
being continuous in one direction, the
homopolar motor needs no commutator
but still requires slip rings. The name
homopolar indicates that the electrical
polarity of the conductor and the
magnetic field poles do not change (i.e.,
that it does not require commutation).

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In effect it was a highly sensitive
thermoresistor which could recover
amplitude modulated signals, something
that the coherer (the standard detector
of the time) could not do.
The first device used to demodulate
audio signals, it was later superseded by
the electrolytic detector, also generally
attributed to Fessenden. The barretter
principle is still used as a detector
for microwave radiation, similar to a
bolometer.

Horsepower
H

Horsepower refers to the power an
engine produces. It’s calculated through
the power needed to move 550 pounds
one foot in one second or by the power
needs to move 33,000 pounds one foot
in one minute.

Hot-Swap
A power supply line controller which
allows circuit boards or other devices
to be removed and replaced while the
system remains powered up. Hotswap
devices typically protect against
overvoltage, undervoltage, and inrush
current that can cause faults, errors, and
hardware damage.

Hot Carrier Diode
A diode realized via a “Schottky-barrier
junction” -- a metal-semiconductor
junction -- rather than the P-N junction
used by conventional semiconductor
diodes. Schottky diodes are often chosen
for their high switching speed and low
forward voltage drop.

Hot wire barretter
The hot wire barretter was a
demodulating detector, invented in
1902 by Reginald Fessenden, that found
limited use in early radio receivers.

HP-IB
General Purpose Interface Bus: A
standard bus for controlling electronic
instruments with a computer. Also
called IEEE-488 bus because it is defined
by ANSI/IEEE Standards 488-1978,
and 488.2-1987. Also called HP-IB, a
trademarked term of Hewlett-Packard,
which invented the protocol.

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Hradec substation
Hradec substation (Czech: přep. stanice
Hradec) is a substation connecting the
220 kV and 400 kV grid in the Czech
Republic’s electricity grid. It is situated
near Hradec u Kadaně in northern
Bohemia. In Hradec the high voltage
transmission lines from the surrounding
lignite-fired power stations come
together and the distribution of load
takes place. Hradec is starting point of
two high voltage transmission lines to
Germany, a 400 kV line to Röhrsdorf in
Saxony and a 400 kV line to Etzenricht
in Bavaria. The transmission capacity of
the line to Röhrsdorf, which went into
service during 1976, is 2640 MW. The
220 kV link to Zwönitz, which was built
in the 1950s, no longer exists. There are
direct 400 kV interconnections from the
substation to Tušimice and Prunéřov
power stations.

conditions need to be maintained such
as a refrigerator, greenhouse, or climatecontrolled warehouse. When adjusting
the controls in these applications the
humidistat would be what is being
set. In microwaves they are used in
conjunction with “smart cooking”
one-button features such as those
for microwave popcorn. Humidistats
employ hygrometers but are not the
same. A humidistat has the functionality
of a switch and is not just a measuring
instrument like a hygrometer is.
For heating, ventilation, and air
conditioning (HVAC) of buildings,
humidistats or humidity sensors are
used to sense the air relative humidity
in the controlled space and turn on and
off the HVAC equipment.

Hybrid
Humidistat
A humidistat is an electronic device
analogous to a thermostat but which
responds to relative humidity, not
temperature. Humidistats are used
in a number of devices including
dehumidifiers, humidifiers, and
microwave ovens. In humidifiers and
dehumidifiers the humidistat is used
where constant relative humidity

Combination of two or more different
elements and having characteristics of
both or all.

Hybrid coil
A hybrid coil (or bridge transformer,
or sometimes hybrid) is a transformer
that has three windings, and which is
designed to be configured as a circuit
having four ports that are conjugate

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in pairs. A signal arriving at one port
is divided equally between the two
adjacent ports but does not appear at the
opposite port. In the schematic diagram,
the signal into W splits between X and
Z, and no signal passes to Y. Similarly,
signals into X split to W and Y with
none to Z, etc.

H

Correct operation requires matched
characteristic impedance at all four
ports. Hybrids are a class of directional
coupler in which the input port power
is split equally between the two output
ports. Forms of hybrid other than
transfomer coils are possible; any format
of directional coupler can be designed
to be a hybrid. These formats include
transmission lines and waveguides.

Hybrid electric vehicle
A hybrid electric vehicle (HEV) is a
type of hybrid vehicle that combines a
conventional internal combustion engine
(ICE) system with an electric propulsion
system (hybrid vehicle drivetrain). The
presence of the electric powertrain is
intended to achieve either better fuel
economy than a conventional vehicle or
better performance. There is a variety
of HEV types, and the degree to which
each functions as an electric vehicle (EV)
also varies. The most common form of
HEV is the hybrid electric car, although
hybrid electric trucks (pickups and
tractors) and buses also exist.

Hybrid Synergy Drive
Hybrid Synergy Drive (HSD) is the brand
name of Toyota Motor Corporation for
the hybrid car drive train technology
used in vehicles with the Toyota and
Lexus marques. First introduced on the
Prius, the technology is an option on
several other Toyota and Lexus vehicles
and has been adapted for the electric
drive system of the hydrogen-powered
Mirai, and for a plug-in hybrid version
of the Prius. Previously, Toyota also
licensed its HSD technology to Nissan
for use in its Nissan Altima Hybrid.
Its parts supplier Aisin Seiki Co. offers
similar hybrid transmissions to other
car companies.
HSD technology produces a full
hybrid vehicle which allows the car
to run on the electric motor only, as
opposed to most other brand hybrids
which cannot and are considered
mild hybrids. The HSD also combines
an electric drive and a planetary
gearset which performs similarly to a
continuously variable transmission. The
Synergy Drive is a drive-by-wire system
with no direct mechanical connection
between the engine and the engine
controls: both the gas pedal/accelerator

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and the gearshift lever in an HSD car
merely send electrical signals to a
control computer.

tantalum, and niobium become brittle
and fracture due to the introduction
and subsequent diffusion of hydrogen
into the metal. The term itself is also a
misnomer when used to describe steels: a
more accurate term would be hydrogenassisted cracking or environmentallyassisted cracking, because the steel (or
other alloys which do not form hydrides)
does not actually become brittle.

H

Hydroelectricity
Hydroelectricity is electricity produced
from hydropower. In 2015 hydropower
generated 16.6% of the world’s total
electricity and 70% of all renewable
electricity, and was expected to increase
about 3.1% each year for the next 25
years.
Hydropower is produced in
150 countries, with the Asia-Pacific
region generating 33 percent of global
hydropower in 2013. China is the largest
hydroelectricity producer, with 920 TWh
of production in 2013, representing 16.9
percent of domestic electricity use.

Hydropower
Hydropower or water power (from
Greek: ύδωρ, “water”) is power derived
from the energy of falling water or
fast running water, which may be
harnessed for useful purposes. Since
ancient times, hydropower from many
kinds of watermills has been used as a
renewable energy source for irrigation
and the operation of various mechanical
devices, such as gristmills, sawmills,
textile mills, trip hammers, dock cranes,
domestic lifts, and ore mills. A trompe,
which produces compressed air from
falling water, is sometimes used to
power other machinery at a distance.

Hydrogen embrittlement
Hydrogen embrittlement is the process
by which hydride-forming metals such
as titanium, vanadium, zirconium,
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the deformation of rubber bands and
shape-memory alloys and many other
natural phenomena. In natural systems
it is often associated with irreversible
thermodynamic change such as phase
transitions and with internal friction;
and dissipation is a common side effect.

Hysteresis
H

Hysteresis is the dependence of the
state of a system on its history. For
example, a magnet may have more
than one possible magnetic moment in
a given magnetic field, depending on
how the field changed in the past. Plots
of a single component of the moment
often form a loop or hysteresis curve,
where there are different values of one
variable depending on the direction of
change of another variable. This history
dependence is the basis of memory in
a hard disk drive and the remanence
that retains a record of the Earth’s
magnetic field magnitude in the past.
Hysteresis occurs in ferromagnetic and
ferroelectric materials, as well as in

Hz
A measure of frequency. An older term
is cycles per second, or cps.

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Ii

I2L

i-type semiconductor
An intrinsic semiconductor, also called
an undoped semiconductor or i-type
semiconductor, is a pure semiconductor
without any significant dopant species
present. The number of charge
carriers is therefore determined by the
properties of the material itself instead
of the amount of impurities. In intrinsic
semiconductors the number of excited
electrons and the number of holes are
equal: n = p.

Integrated injection logic (IIL, I2L, or
I2L) is a class of digital circuits built
with multiple collector bipolar junction
transistors (BJT). When introduced it
had speed comparable to TTL yet was
almost as low power as CMOS, making
it ideal for use in VLSI (and larger)
integrated circuits.

I

Ideal crystal
Ideal crystal is a single crystal with a
perfectly regular lattice that contains
no impurities, imperfections, or other
defects.

I/O
In computing, input/output (I/O, or
informally io or IO) is the communication
between an information processing
system, such as a computer, and the
outside world, possibly a human or
another information processing system.

IEC61850
IEC 61850 is an international standard
defining communication protocols for
intelligent electronic devices at electrical
substations. It is a part of the International
Electrotechnical Commission’s (IEC)
Technical Committee 57 reference
architecture for electric power systems.
The abstract data models defined in
IEC 61850 can be mapped to a number
of protocols. Current mappings in the
standard are to MMS (Manufacturing

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Message Specification), GOOSE (Generic
Object Oriented Substation Event), SMV
(Sampled Measured Values), and soon
to Web Services. These protocols can
run over TCP/IP networks or substation
LANs using high speed switched Ethernet
to obtain the necessary response times
below four milliseconds for protective
relaying.

IEEE Electromagnetic
Compatibility Society
The IEEE Electromagnetic Compatibility
Society (EMCS) is an organizational unit
and professional society of academic
professors and applied engineers with
a common interest, affiliated with
the IEEE. The 50-year-old Society has
members and chapters in nearly every
country throughout the world.

I

IEEE Broadcast
Technology Society
The Institute of Electrical and Electronics
Engineers (IEEE) is a professional
association with its corporate office in
New York City and its operations center
in Piscataway, New Jersey. It was formed
in 1963 from the amalgamation of the
American Institute of Electrical Engineers
and the Institute of Radio Engineers.
Today, it is the world’s largest association
of technical professionals with more than
420,000 members in over 160 countries
around the world. Its objectives are the
educational and technical advancement
of electrical and electronic engineering,
telecommunications, and computer
engineering and allied disciplines.

IEEE Power & Energy
Society
The IEEE Power & Energy Society (PES),
formerly the IEEE Power Engineering
Society, is the oldest society of the
Institute of Electrical and Electronics
Engineers (IEEE) focused on the
scientific and engineering knowledge
about electric power and energy.

IGBT
An insulated-gate bipolar transistor
(IGBT) is a three-terminal power
semiconductor device primarily used
as an electronic switch which, as it
was developed, came to combine high
efficiency and fast switching. It switches
electric power in many applications:
variable-frequency drives (VFDs), electric

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cars, trains, variable speed refrigerators,
lamp ballasts, air-conditioners and even
stereo systems with switching amplifiers.
The IGBT is a semiconductor device
with four alternating layers (P-N-P-N)
that are controlled by a metal-oxidesemiconductor (MOS) gate structure
without regenerative action.

computer algorithms to perform image
processing on digital images. As a
subcategory or field of digital signal
processing, digital image processing has
many advantages over analog image
processing. It allows a much wider range
of algorithms to be applied to the input
data and can avoid problems such as the
build-up of noise and signal distortion
during processing. Since images are
defined over two dimensions (perhaps
more) digital image processing may be
modeled in the form of multidimensional
systems.
I

Image impedance
Image impedance is a concept used in
electronic network design and analysis
and most especially in filter design. The
term image impedance applies to the
impedance seen looking into a port of
a network. Usually a two-port network
is implied but the concept can extended
to networks with more than two ports.
The definition of image impedance for
a two-port network is the impedance,
Zi 1, seen looking into port 1 when
port 2 is terminated with the image
impedance, Zi 2, for port 2. In general,
the image impedances of ports 1 and 2
will not be equal unless the network is
symmetrical (or anti-symmetrical) with
respect to the ports.

Image processing
Digital image processing is the use of

Impedance Bridge
A bridge circuit used for measuring
resistance and reactance.

Impedance Matching
The connection of an additional
impedance to an existing one in order
to accomplish a specific effect, such as to
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balance a circuit or to reduce reflection
in a transmission line. The matching of
impedances from one circuit to another
to insure optimum power transfer.

response, or impulse response function
(IRF), of a dynamic system is its output
when presented with a brief input signal,
called an impulse. More generally, an
impulse response is the reaction of any
dynamic system in response to some
external change. In both cases, the
impulse response describes the reaction
of the system as a function of time (or
possibly as a function of some other
independent variable that parameterizes
the dynamic behavior of the system).

I

Incandescent lamp

Impulse
A short surge of electrical, magnetic, or
electromagnetic energy. A unidirectional
voltage that rises rapidly and then
decays to zero at a slower rate.

Impulse Noise
Noise consisting of random occurrences
of energy spikes having random
amplitude and spectral content. Note:
Impulse noise in a data channel can be
a definitive cause of data transmission
errors. Noise generated in discrete
energy bursts which has a characteristic
wave shape.

Impulse response
In signal processing, the impulse

An incandescent light bulb, incandescent
lamp or incandescent light globe is an
electric light with a wire filament heated
to such a high temperature that it glows
with visible light (incandescence). The
filament, heated by passing an electric
current through it, is protected from
oxidation with a glass or fused quartz
bulb that is filled with inert gas or
evacuated. In a halogen lamp, filament
evaporation is slowed by a chemical
process that redeposits metal vapor
onto the filament, extending its life.
The light bulb is supplied with electric
current by feed-through terminals or
wires embedded in the glass. Most bulbs
are used in a socket which provides
mechanical support and electrical
connections.
Incandescent
bulbs
are
manufactured in a wide range of sizes,

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light output, and voltage ratings, from
1.5 volts to about 300 volts. They require
no external regulating equipment, have
low manufacturing costs, and work
equally well on either alternating
current or direct current. As a result,
the incandescent lamp is widely used in
household and commercial lighting, for
portable lighting such as table lamps,
car headlamps, and flashlights, and for
decorative and advertising lighting.

Incident Wave
The wave that strikes the surface of a
medium. The wave that travels from
the sending end to the receiving end
of a transmission line.

Induction coil
An induction coil or “spark coil”
(archaically known as an inductorium
or Ruhmkorff coil after Heinrich
Ruhmkorff) is a type of electrical
transformer used to produce highvoltage pulses from a low-voltage
direct current (DC) supply. To create
the flux changes necessary to induce
voltage in the secondary coil, the direct
current in the primary coil is repeatedly
interrupted by a vibrating mechanical
contact called an interrupter. Invented in
1836 by Nicholas Callan, Charles Page
and others, the induction coil was the
first type of transformer. It was widely
used in x-ray machines, spark-gap radio
transmitters, arc lighting and quack
medical electrotherapy devices from
the 1880s to the 1920s. Today its only
common use is as the ignition coils
in internal combustion engines and
in physics education to demonstrate
induction.

In-Circuit Meter
A meter permanently installed in a
circuit; used to monitor circuit operation.

Induction generator
An induction generator or asynchronous
generator is a type of alternating current
(AC) electrical generator that uses
the principles of induction motors to
produce power. Induction generators
operate by mechanically turning their
rotors faster than synchronous speed.
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A regular AC induction motor usually
can be used as a generator, without
any internal modifications. Induction
generators are useful in applications
such as mini hydro power plants, wind
turbines, or in reducing high-pressure
gas streams to lower pressure, because
they can recover energy with relatively
simple controls.

I

Induction regulator
An induction regulator is an alternating
current electrical machine, somewhat
similar to an induction motor, which can
provide a continuously variable output
voltage. The induction regulator was an
early device used to control the voltage
of electric networks. Since the 1930s it has
been replaced in distribution network
applications by the tap transformer.
Its usage is now mostly confined to
electrical laboratories, electrochemical
processes and arc welding. With minor
variations, its setup can be used as an
phase-shifting power transformer.

Induction motor
An induction motor or asynchronous
motor is an AC electric motor in
which the electric current in the rotor
needed to produce torque is obtained
by electromagnetic induction from the
magnetic field of the stator winding.
An induction motor can therefore be
made without electrical connections to
the rotor.[a] An induction motor’s rotor
can be either wound type or squirrelcage type.

Inductive coupling
In electrical engineering, two conductors
are referred to as inductively coupled
or magnetically coupled when they
are configured such that a change in
current through one wire induces a
voltage across the ends of the other wire
through electromagnetic induction. The
amount of inductive coupling between
two conductors is measured by their
mutual inductance.

Inductor
An inductor, also called a coil, choke
or reactor, is a passive two-terminal
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their steady-state currents, due to the
charging current of the input capacitance.
The selection of overcurrent-protection
devices such as fuses and circuit
breakers is made more complicated
when high inrush currents must be
tolerated. The overcurrent protection
must react quickly to overload or shortcircuit faults but must not interrupt the
circuit when the (usually harmless)
inrush current flows.

electrical component that stores electrical
energy in a magnetic field when electric
current flows through it. An inductor
typically consists of an insulated wire
wound into a coil around a core.

I

Information appliance
An information appliance (IA) is an
appliance that is designed to easily
perform a specific electronic function
such as playing music, photography,
or editing text.
Typical examples are smartphones
and personal digital assistants (PDAs).
Information appliances partially overlap
in definition with, or are sometimes
referred to as smart devices, embedded
systems, mobile devices or wireless
devices.

Inrush current
Inrush current, input surge current
or switch-on surge is the maximal
instantaneous input current drawn by
an electrical device when first turned on.
Alternating-current electric motors and
transformers may draw several times
their normal full-load current when first
energized, for a few cycles of the input
waveform. Power converters also often
have inrush currents much higher than

Instrumentation
Instrumentation is a collective term
for measuring instruments used for
indicating, measuring and recording
physical quantities, and has its origins
in the art and science of Scientific
instrument-making.
The term instrumentation may refer
to a device or group of devices used for
direct reading thermometers or, when
using many sensors, may become part of
a complex Industrial control system in
such as manufacturing industry, vehicles
and transportation. Instrumentation can
be found in the household as well; a
smoke detector or a heating thermostat
are examples.

Insulation monitoring
device
An insulation monitoring device
monitors the ungrounded system
between an active phase conductor and

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earth. It is intended to give an alert (light
and sound) or disconnect the power
supply when the resistance between
the two conductors drops below a set
value, usually 50 kΩ (sample of IEC
standard for medical applications). The
main advantage is that the ungrounded
or floating system allows a continuous
operation of important consumers such
as medical, chemical, military, etc.

I

Insulator (electrical)
An electrical insulator is a material
whose internal electric charges do not
flow freely; very little electric current
will flow through it under the influence
of an electric field. This contrasts with
other materials, semiconductors and
conductors, which conduct electric
current more easily. The property that
distinguishes an insulator is its resistivity;
insulators have higher resistivity than
semiconductors or conductors.

Integrated circuit
An integrated circuit or monolithic
integrated circuit (also referred to as
an IC, a chip, or a microchip) is a set of
electronic circuits on one small flat piece
(or “chip”) of semiconductor material,
normally silicon. The integration of
large numbers of tiny transistors into
a small chip results in circuits that are
orders of magnitude smaller, cheaper,
and faster than those constructed of
discrete electronic components. The IC’s
mass production capability, reliability
and building-block approach to circuit
design has ensured the rapid adoption
of standardized ICs in place of designs
using discrete transistors. ICs are now
used in virtually all electronic equipment
and have revolutionized the world of
electronics. Computers, mobile phones,
and other digital home appliances are
now inextricable parts of the structure
of modern societies, made possible by
the small size and low cost of ICs.

Intelligent control
Intelligent control is a class of control
techniques that use various artificial
intelligence computing approaches like
neural networks, Bayesian probability,
fuzzy logic, machine learning,
evolutionary computation and genetic
algorithms.
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Intermittent energy source
An intermittent energy source is any
source of energy that is not continuously
available for conversion into electricity
and outside direct control because the
used primary energy cannot be stored.
Intermittent energy sources may be
predictable but cannot be dispatched
to meet the demand of an electric power
system.
The use of intermittent sources
in an electric power system usually
displaces storable primary energy
that would otherwise be consumed by
other power stations. Another option
is to store electricity generated by nondispatchable energy sources for later
use when needed, e.g. in the form of
pumped storage, compressed air or in
batteries. A third option is the sector
coupling e.g. by electrode heating for
district heating schemes.

Internal combustion engine
An internal combustion engine (ICE) is
a heat engine where the combustion of
a fuel occurs with an oxidizer (usually
air) in a combustion chamber that is
an integral part of the working fluid
flow circuit. In an internal combustion
engine, the expansion of the hightemperature and high-pressure gases
produced by combustion applies direct

force to some component of the engine.
The force is applied typically to pistons,
turbine blades, rotor or a nozzle. This
force moves the component over a
distance, transforming chemical energy
into useful mechanical energy.

I

International
Electrotechnical
Commission (IEC)
The International Electrotechnical
Commissio (IEC; in French: Commission
électrotechnique internationale) is an
international standards organization that
prepares and publishes International
Standards for all electrical, electronic
and related technologies – collectively
known as “electrotechnology”. IEC
standards cover a vast range of
technologies from power generation,
transmission and distribution to home
appliances and office equipment,
semiconductors, fibre optics, batteries,
solar energy, nanotechnology and
marine energy as well as many others.
The IEC also manages three global
conformity assessment systems that
certify whether equipment, system or
components conform to its International
Standards.

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Inverter
A power inverter, or inverter, is an
electronic device or circuitry that changes
direct current (DC) to alternating current
(AC).

used to transfer electrical power from a
source of alternating current (AC) power
to some equipment or device while
isolating the powered device from the
power source, usually for safety reasons.
Isolation transformers provide galvanic
isolation and are used to protect against
electric shock, to suppress electrical
noise in sensitive devices, or to transfer
power between two circuits which
must not be connected. A transformer
sold for isolation is often built with
special insulation between primary and
secondary, and is specified to withstand
a high voltage between windings.

I

The input voltage, output voltage
and frequency, and overall power
handling depend on the design of the
specific device or circuitry. The inverter
does not produce any power; the power
is provided by the DC source.

Isolation transformer
An isolation transformer is a transformer

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Jj
j operator
In computer science, Peter Landin’s J
operator is a programming construct
that post-composes a lambda expression
with the continuation to the current
lambda-context. The resulting “function”
is first-class and can be passed on to
subsequent functions, where if applied it
will return its result to the continuation
of the function in which it was created.

Jack plug and socket
Jack plugs and sockets are widely found
in audio and audio-video applications
and are most commonly used for
analogue audio signals.

Jabber

J

A condition wherein a station transmits
for a period of time longer than the
maximum permissible packet length,
usually due to a fault condition. In local
area networks, transmission by a data
station beyond the time interval allowed
by the protocol.

Jack Screw
A threaded jack. A female post used
to accept a bolt or other threaded
part. Refer to the jack-post graphic in
the right side-bar. A locking device
specifically designed to secure engaged
electrical connectors. Its mating end is
either internally or externally threaded.

Jack
A socket. A receptacle. The fixed portion
of a two connector system. The female
end of a mating connector which accepts
a Plug. An example Banana Jack, or
panel-mount Test Jack is shown in the
graphic. Also see Jack & Plug Vendors.

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Jacket
The outermost layer of insulating
material of a cable or harness. The
outer sheath which protects a cable. The
outer sheath or covering material,such
as natural or synthetic rubber, lead
sheath,steel tape, or a thermoplastic
compound, applied over a singleinsulated conductor or over an assembly
of insulated conductors for protection
against crushing,cutting,and abrasion
of the conductors and their insulation.

Jamming
J

Jamming is the physical process by
which the viscosity of some mesoscopic
materials, such as granular materials,
glasses, foams, polymers, emulsions,
and other complex fluids, increases with
increasing particle density.

semiconductor engineering trade
organization and standardization body
headquartered in Arlington, Virginia,
United States. JEDEC has over 300
members, including some of the world’s
largest computer companies.

JFET
Junction FET, a voltage controlled
transistor and not current controlled. A
transistor in which the conduction is due
entirely to the flow of majority carriers
through a conduction channel controlled
by an electric field arising from a voltage
applied between the gate and source
terminals. [FET Manufacturers] and
vendors. An N-Channel FET is shown
to the right.

JFIF
The JPEG File Interchange Format (JFIF)
is an image file format standard. It
defines supplementary specifications
for the container format that contains
the image data encoded with the JPEG
algorithm.

Jansky noise
Jansky Noise has been instrumental
in V/Vm Test helping set up the label
back in 1996 and has since worked
very closely on numerous projects on
the label. As well as his work with V/
Vm he has also worked closely with
Speedranch and Animal.

JEDEC
The JEDEC Solid State Technology
Association is an independent

Jitter
Jitter is the difference [deviation]
between the expected occurrence of
a signal edge and the time the edge

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Junction

actually occurs [phase variation]. Jitter
may also be expressed as the movement
of a signal edge from its ideal position
in time [the expected position]. Abrupt
and unwanted variations of one or
more signal characteristics, such as the
interval between successive pulses, the
amplitude of successive cycles, or the
frequency or phase of successive cycles.
Read more on Signal Jitter.

The connection between two or more
conductors. The contact between two
dissimilar metals or materials, as in a
thermocouple. A region of transition
between semiconductor layers, such
as a p/n junction, which goes from a
region that has a high concentration
of acceptors (p-type) to one that has a
high concentration of donors (n-type).

Josephson effect
The Josephson effect is the phenomenon
of supercurrent, a current that flows
continuously without any voltage
applied, across a device known as a
Josephson junction, which consists of
two or more superconductors coupled
by a weak link.

Junction Box
A box with a cover that serves the
purpose of joining different runs of
wire or cable and provides space for
the connection and branching of the
enclosed conductors. An enclosure of
other than cast metal designed to house,
mount, and protect, but does not include
wiring connections or electrical devices
such as terminals, terminal boards,
switches, jacks, fuse-holders, connectors,
or circuit breakers.

Joule effect
Joule effect and Joule’s law are any
of several different physical effects
discovered or characterized by English
physicist James Prescott Joule.

Junction Diode
A two-terminal device containing a single
crystal of semi-conducting material that
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ranges from P-type at one terminal
to N-type at the other. Also refer to
Diode Manufacturers. A semiconductor
device with a junction and a built-in
potential that passes current better in
one direction than the other. All solar
cells are junction diodes.

Junction Transistor
A bipolar transistor constructed from
interacting PN junctions. The term is
used to distinguish junction transistors
from other types, such as field-effect
and point-contact. Reference; Transistor
Terms, and BJT Manufacturers.

J

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Kk

microwave part of the electromagnetic
spectrum defined as frequencies in the
range 26.5–40 gigahertz, i.e. wavelengths
from slightly over one centimeter down
to 7.5 millimeters.

K-map
The Karnaugh map (KM or K-map)
is a method of simplifying
Boolean
algebra
expressions.
Maurice Karnaugh introduced it in 1953
as a refinement of Edward W.

Kaiser window
The Kaiser window, also known as the
Kaiser–Bessel window, was developed
by James Kaiser at Bell Laboratories. It
is a one-parameter family of window
functions used in finite impulse response
filter design and spectral analysis.

K band
K-space
K-space is a formalism widely used in
magnetic resonance imaging introduced
in 1979 by Likes and in 1983 by Ljunggren
and Twieg. In MRI physics, k-space is
the 2D or 3D Fourier transform of the
MR image measured.

A portion of the Electromagnetic
Spectrum in the Microwave region of
frequencies ranging between 12 and 93
gigahertz (GHz).

Kalman filter
Ka band
The Ka band is a portion of the

Kalman filtering, also known as
linear quadratic estimation (LQE),
is an algorithm that uses a series of
measurements observed over time,
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containing statistical noise and other
inaccuracies, and produces estimates
of unknown variables that tend to be
more accurate than those based on a
single measurement alone, by estimating
a joint probability distribution over the
variables for each timeframe. The filter
is named after Rudolf E. Kálmán, one
of the primary developers of its theory.

Kelvin contacts
The Kelvin contacts are named after the
physicist Baron Kelvin. Kelvin made
it possible to measure the slightest
resistance with a small measuring
current.
K

Kelvin effect
The effect whereby the vapour pressure
over a curved surface (e.g. that of a
water droplet) is greater than that over
a flat plane. The smaller the radius, the
greater the vapour pressure. The effect is
particularly important for the process
of condensation and for small droplets
(such as those in clouds).

Kilovolt-ampere
Kelvin double bridge
A kelvin bridge or kelvin double
bridge is a modified version of the
Wheatstone bridge, which can measure
resistance values in the range between
1 to 0.00001 ohms with high accuracy.
It is named because it uses another set
of ratio arms and a galvanometer to
measure the unknown resistance value.

A volt-ampere (VA) is the unit used
for the apparent power in an electrical
circuit, equal to the product of rootmean-square (RMS) voltage and RMS
current. In direct current (DC) circuits,
this product is equal to the real power
(active power) in watts. Volt-amperes are
useful only in the context of alternating
current (AC) circuits (sinusoidal voltages
and currents of the same frequency).

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Klystron
Kirchhoff’s circuit laws
Kirchhoff ’s circuit laws are two
equalities that deal with the current and
potential difference (commonly known
as voltage) in the lumped element model
of electrical circuits. They were first
described in 1845 by German physicist
Gustav Kirchhoff. This generalized the
work of Georg Ohm and preceded the
work of James Clerk Maxwell. Widely
used in electrical engineering, they are
also called Kirchhoff’s rules or simply
Kirchhoff’s laws.

A klystron is a specialized linear-beam
vacuum tube, invented in 1937 by
American electrical engineers Russell
and Sigurd Varian, which is used as
an amplifier for high radio frequencies,
from UHF up into the microwave
range. Low-power klystrons are used
as oscillators in terrestrial microwave
relay communications links, while highpower klystrons are used as output
tubes in UHF television transmitters,
satellite communication, and radar
transmitters, and to generate the drive
power for modern particle accelerators.

Both of Kirchhoff’s laws can be
understood as corollaries of Maxwell’s
equations in the low-frequency limit.
They are accurate for DC circuits, and
for AC circuits at frequencies where
the wavelengths of electromagnetic
radiation are very large compared to
the circuits.

Kirchhoff’s voltage law
Kirchhoff’s voltage law states that the
sum of the voltage differences around
any closed loop in a circuit must be zero.
A loop in a circuit is any path which
ends at the same point at which it starts.

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Kolmogorov backward
equation
In probability theory, Kolmogorov
equations, including Kolmogorov
forward equations and Kolmogorov
backward equations, characterize
stochastic processes. In particular, they
describe how the probability that a
stochastic process is in a certain state
changes over time.

K

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Ll

LAN

L-C network
Some sine-wave oscillators use resonant
circuits consisting of inductance and
capacitance.

A local area network (LAN) is a
computer network that interconnects
computers within a limited area such
as a residence, school, laboratory,
university campus or office building.
By contrast, a wide area network (WAN)
not only covers a larger geographic
distance, but also generally involves
leased telecommunication circuits.
Ethernet and Wi-Fi are the two most
common technologies in use for local
area networks. Historical technologies
include ARCNET, Token ring, and
AppleTalk.

L

L-section
An L-section beam type has fewer than
two planes of symmetry. Therefore,
make sure the beam is loaded or braced
to prevent twist under shear loading.

Ladder network

Laplace transform

A network consisting of circuit
elements connected in series and in
parallel. The circuit elements may be
resistors, inductance coils, or capacitors.
A ladder network may be described
as a cascade connection of a series of
symmetrical T-section or pi-section fourterminal networks.

The Laplace transform is very similar
to the Fourier transform. While the
Fourier transform of a function is a
complex function of a real variable
(frequency), the Laplace transform of
a function is a complex function of a
complex variable. Laplace transforms
are usually restricted to functions of
t with t ≥ 0. A consequence of this
restriction is that the Laplace transform
of a function is a holomorphic function
of the variable s. Unlike the Fourier
transform, the Laplace transform of a
distribution is generally a well-behaved
function. Also techniques of complex
variables can be used directly to study

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Laplace transforms. As a holomorphic
function, the Laplace transform has
a power series representation. This
power series expresses a function as
a linear superposition of moments
of the function. This perspective has
applications in probability theory.

Large scale integration
Large-scale integration (LSI) is the
process of integrating or embedding
thousands of transistors on a single
silicon semiconductor microchip.
LSI technology was conceived in the
mid-1970s when computer processor
microchips were under development.
LSI is no longer in use.

L

Leakage inductance
Leakage inductance is that property of
an electrical transformer that causes a
winding to appear to have some pure
inductance in series with the mutuallycoupled transformer windings.
Usually, this is an undesirable
property, but it is sometimes deliberately
introduced into a transformer that is
used as a ballast for a gas discharge
lamp such as a fluorescent lamp, or in a
transformer used for arc welding. In this
case, the leakage inductance limits the
current flow to the desired magnitude.
Leakage inductance is primarily
controlled by the design of the windings
and the geometry of the magnetic core
used to form the transformer.

Laser diode
A laser diode, (LD), injection laser diode
(ILD), or diode laser is a semiconductor
device similar to a light-emitting diode
in which the laser beam is created
at the diode’s junction. Laser diodes
are the most common type of lasers
produced, with a wide range of uses
that include fiber optic communications,
barcode readers, laser pointers, CD/
DVD/Blu-ray disc reading/recording,
laser printing, laser scanning and light
beam illumination.

Light-dependent resistor
LDR (Light Dependent Resistor) as the
name states is a special type of resistor
that works on the photoconductivity
principle means that resistance changes
according to the intensity of light. Its

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resistance decreases with an increase in
the intensity of light.

motor used as an electrical generator.
An alternator is a type of alternating
current (AC) electrical generator. The
devices are often physically equivalent.
The principal difference is in how they
are used and which direction the energy
flows. An alternator converts mechanical
energy to electrical energy, whereas
a motor converts electrical energy to
mechanical energy. Like most electric
motors and electric generators, the
linear alternator works by the principle
of electromagnetic induction. However,
most alternators work with rotary
motion, whereas “linear” alternators
work with “linear” motion (i.e. motion
in a straight line).

Light-emitting diode
A light-emitting diode (LED) is a twolead semiconductor light source. It is
a p–n junction diode that emits light
when activated. When a suitable current
is applied to the leads, electrons are
able to recombine with electron holes
within the device, releasing energy in
the form of photons. This effect is called
electroluminescence, and the color of the
light (corresponding to the energy of the
photon) is determined by the energy
band gap of the semiconductor. LEDs
are typically small (less than 1 mm2)
and integrated optical components may
be used to shape the radiation pattern.

Linear motor

Linear alternator

Lineman (occupation)

A linear alternator is essentially a linear

A lineworker (lineman (American

A linear motor is an electric motor that
has had its stator and rotor “unrolled”
so that instead of producing a torque
(rotation) it produces a linear force along
its length. However, linear motors are not
necessarily straight. Characteristically, a
linear motor’s active section has ends,
whereas more conventional motors are
arranged as a continuous loop.

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English), linesman (British English),
powerline technician (PLT), or
powerline worker) is a tradesperson
who constructs and maintains electric
power transmission and distribution
lines.
A lineworker generally does
outdoor installation and maintenance
jobs. Those who install and maintain
electrical wiring inside buildings are
electricians.

L

Liquid crystal display
A liquid-crystal display is a flatpanel display or other electronically
modulated optical device that uses the
light-modulating properties of liquid
crystals combined with polarizers.
Liquid crystals do not emit light
directly but instead use a backlight or
reflector to produce images in color or
monochrome.

Litz wire
Litz wire is a type of specialized
multistrand wire or cable used in
electronics to carry alternating current
(AC) at radio frequencies. The wire is
designed to reduce the skin effect and
proximity effect losses in conductors
used at frequencies up to about 1 MHz.
It consists of many thin wire strands,
individually insulated and twisted
or woven together, following one of
several carefully prescribed patterns
often involving several levels (groups of
twisted wires are twisted together, etc.).
The result of these winding patterns is
to equalize the proportion of the overall
length over which each strand is at the
outside of the conductor. This has the
effect of distributing the current equally
among the wire strands, reducing the
resistance. Litz wire is used in high
Q inductors for radio transmitters and
receivers operating at low frequencies,
induction heating equipment and
switching power supplies.

Load flow study
In power engineering, the power-flow
study, or load-flow study, is a numerical
analysis of the flow of electric power in
an interconnected system. A power-flow
study usually uses simplified notations
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such as a one-line diagram and perunit system, and focuses on various
aspects of AC power parameters, such
as voltages, voltage angles, real power
and reactive power. It analyzes the
power systems in normal steady-state
operation.
Power-flow or load-flow studies
are important for planning future
expansion of power systems as well
as in determining the best operation
of existing systems. The principal
information obtained from the powerflow study is the magnitude and phase
angle of the voltage at each bus, and
the real and reactive power flowing in
each line.

Load following power
plant
A load following power plant, regarded
as producing mid-merit or mid-priced
electricity, is a power plant that adjusts
its power output as demand for
electricity fluctuates throughout the day.
Load following plants are typically inbetween base load and peaking power
plants in efficiency, speed of startup
and shut down, construction cost, cost
of electricity and capacity factor.

Load management
Load management, also known as
demand side management (DSM), is
the process of balancing the supply
of electricity on the network with the
electrical load by adjusting or controlling
the load rather than the power station
output. This can be achieved by direct
intervention of the utility in real time,
by the use of frequency sensitive relays
triggering the circuit breakers (ripple
control), by time clocks, or by using
special tariffs to influence consumer
behavior. Load management allows
utilities to reduce demand for electricity
during peak usage times (peak shaving),
which can, in turn, reduce costs by
eliminating the need for peaking power
plants. In addition, some peaking
power plants can take more than an
hour to bring on-line which makes load
management even more critical should
a plant go off-line unexpectedly for
example. Load management can also
help reduce harmful emissions, since
peaking plants or backup generators
are often dirtier and less efficient than
base load power plants. New loadmanagement technologies are constantly
under development — both by private
industry and public entities.

Load profile
In electrical engineering, a load profile is
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a graph of the variation in the electrical
load versus time. A load profile will
vary according to customer type
(typical examples include residential,
commercial and industrial), temperature
and holiday seasons. Power producers
use this information to plan how much
electricity they will need to make
available at any given time. Teletraffic
engineering uses a similar load curve.

This frequency conversion process, also
called heterodyning, produces the sum
and difference frequencies from the
frequency of the local oscillator and
frequency of the input signal.

LORAN
L

Load-loss factor
Load-loss factor (LLF) is a factor which
when multiplied by energy lost at time
of peak and the number of load periods
will give overall average energy lost. It
is calculated as the ratio of the average
load loss to the peak load loss.

LORAN, short for long range navigation,
was a hyperbolic radio navigation
system developed in the United States
during World War II. It was similar to
the UK’s Gee system but operated at
lower frequencies in order to provide
an improved range up to 1,500 miles
(2,400 km) with an accuracy of tens of
miles. It was first used for ship convoys
crossing the Atlantic Ocean, and then
by long-range patrol aircraft, but found
its main use on the ships and aircraft
operating in the Pacific theatre.

Local oscillator
In electronics, a local oscillator (LO) is an
electronic oscillator used with a mixer
to change the frequency of a signal.
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Loss power
Electric power transmission is the bulk
movement of electrical energy from
a generating site, such as a power
plant, to an electrical substation. The
interconnected lines which facilitate this
movement are known as a transmission
network. This is distinct from the
local wiring between high-voltage
substations and customers, which is
typically referred to as electric power
distribution. The combined transmission
and distribution network is known as
the “power grid” in North America, or
just “the grid”. In the United Kingdom,
India, Malaysia and New Zealand, the
network is known as the “National
Grid”.

Low-noise amplifier
A low-noise amplifier (LNA) is an
electronic amplifier that amplifies a very
low-power signal without significantly
degrading its signal-to-noise ratio. An
amplifier increases the power of both
the signal and the noise present at its
input. LNAs are designed to minimize
additional noise. Designers minimize
noise by considering trade-offs that
include impedance matching, choosing
the amplifier technology (such as lownoise components) and selecting lownoise biasing conditions.

Low-noise block
downconverter
A low-noise block downconverter
(LNB) is the receiving device mounted
on satellite dishes used for satellite
TV reception, which collects the radio
waves from the dish and converts them
to a signal which is sent through a cable
to the receiver inside the building. Also
called a low-noise block, low-noise
converter (LNC), or even low-noise
downconverter (LND), the device is
sometimes inaccurately called a lownoise amplifier (LNA).

Low-pass filter
A low-pass filter (LPF) is a filter that
passes signals with a frequency lower
than a certain cutoff frequency and
attenuates signals with frequencies
higher than the cutoff frequency. The
exact frequency response of the filter
depends on the filter design. The filter
is sometimes called a high-cut filter, or
treble-cut filter in audio applications. A
low-pass filter is the complement of a
high-pass filter.

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LSI
Latent semantic analysis is a technique
in natural language processing, in
particular distributional semantics, of
analyzing relationships between a set of
documents and the terms they contain
by producing a set of concepts related
to the documents and terms.

Luminescence

LTP
L

Long-term potentiation is a persistent
strengthening of synapses based on
recent patterns of activity. These are
patterns of synaptic activity that
produce a long-lasting increase in signal
transmission between two neurons.

Luminescence is spontaneous emission
of light by a substance not resulting
from heat; or “cold light”. It is thus a
form of cold-body radiation. It can be
caused by chemical reactions, electrical
energy, subatomic motions or stress on
a crystal.

Lumen (unit)
The lumen (symbol: lm) is the SI derived
unit of luminous flux, a measure of the
total quantity of visible light emitted by
a source. Luminous flux differs from
power (radiant flux) in that radiant
flux includes all electromagnetic waves
emitted, while luminous flux is weighted
according to a model (a “luminosity
function”) of the human eye’s sensitivity
to various wavelengths. Lumens are
related to lux in that one lux is one
lumen per square meter.

Lumped parameters
The lumped element model (also
called lumped parameter model, or
lumped component model) simplifies
the description of the behavior of
spatially distributed physical systems
into a topology consisting of discrete
entities that approximate the behavior
of the distributed system under certain

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assumptions. It is useful in electrical
systems (including electronics),
mechanical multi body systems, heat
transfer, acoustics, etc.

instead of conventional copper coil
windings, and is held together purely by
magnets. The motor provides a power of
15 horsepower (11 kW) and only weighs
11 kilograms (24 lb).

Lynch motor
The Lynch motor is a unique axial gap
permanent magnet brushed DC electric
motor. The motor has a pancake-like
shape and was invented by Cedric
Lynch in 1979, the relevant patent being
filed on 18 December 1986.
The Lynch motor can achieve 90%
efficiency. It is built from ferrite blocks
sandwiched between strips of metal,

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Mm

recognition (OCR), learning to rank, and
computer vision.

Machine code
Machine code is a computer program
written in machine language. It uses the
instruction set of a particular computer
architecture. It is usually written in
binary. Machine code is the lowest
level of software. Other programming
languages are translated into machine
code so the computer can execute them.

Machine Learning

M

Machine learning is a field of computer
science that gives computer systems
the ability to “learn” (i.e. progressively
improve performance on a specific task)
with data, without being explicitly
programmed.
The name Machine learning was
coined in 1959 by Arthur Samuel.
Evolved from the study of pattern
recognition and computational
learning theory in artificial intelligence,
machine learning explores the study
and construction of algorithms that
can learn from and make predictions
on data such algorithms overcome
following strictly static program
instructions by making data-driven
predictions or decisions,: 2 through
building a model from sample inputs.
Machine learning is employed in a range
of computing tasks where designing
and programming explicit algorithms
with good performance is difficult or
infeasible; example applications include
email filtering, detection of network
intruders or malicious insiders working
towards a data breach, optical character

Machine vision
Machine vision is the technology and
methods used to provide imagingbased automatic inspection and analysis
for such applications as automatic
inspection, process control, and robot
guidance, usually in industry.

Macrocell
A macrocell or macrosite is a cell in a
mobile phone network that provides
radio coverage served by a high power
cell site (tower, antenna or mast).
Generally, macrocells provide coverage
larger than microcell.

Macroscopic
The macroscopic scale is the length

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scale on which objects or phenomena
are large enough to be visible almost
practically with the naked eye, without
magnifying optical instruments.

Maglev
Maglev (derived from magnetic
levitation) is a system of train
transportation that uses two sets of
magnets: one set to repel and push the
train up off the track, and another set
to move the elevated train ahead, taking
advantage of the lack of friction.

Magnetic balance test
Magnetic balance test is conducted only
on three-phase transformers to check
the imbalance in the magnetic circuit.

the most notable property of a magnet:
a force that pulls on other ferromagnetic
materials, such as iron, and attracts
or repels other magnets. The overall
strength of a magnet is measured by its
magnetic moment or, alternatively, the
total magnetic flux it produces. The local
strength of magnetism in a material is
measured by its magnetization.

Magnet Wire
Magnet wire or enameled wire is a
copper or aluminium wire coated with
a very thin layer of insulation. It is used
in the construction of transformers,
inductors, motors, speakers, hard disk
head actuators, electromagnets, and
other applications that require tight
coils of insulated wire.

Magnet
A magnet is a material or object that
produces a magnetic field. This magnetic
field is invisible but is responsible for
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Magnetic Blowout

Magnetic Constant

Magnetic blowouts use blowout coils
to lengthen and move the electric arc.
These are especially useful in DC power
circuits. AC arcs have periods of low
current, during which the arc can be
extinguished with relative ease, but DC
arcs have continuous high current, so
blowing them out requires the arc to be
stretched further than an AC arc of the
same current. The magnetic blowouts in
the pictured Albright contactor (which
is designed for DC currents) more
than double the current it can break,
increasing it from 600 A to 1,500 A.

Magnetic constant, is an ideal, (baseline)
physical constant, which is the value
of magnetic permeability in a classical
vacuum. Vacuum permeability is
derived from production of a magnetic
field by an electric current or by a
moving electric charge and in all other
formulas for magnetic-field production
in a vacuum. In the reference medium
of classical vacuum, µ0 has an exact
defined value:

Magnetic Circuit

M

A magnetic circuit is made up of one
or more closed loop paths containing
a magnetic flux. The flux is usually
generated by permanent magnets or
electromagnets and confined to the
path by magnetic cores consisting
of ferromagnetic materials like iron,
although there may be air gaps or other
materials in the path. Magnetic circuits
are employed to efficiently channel
magnetic fields in many devices such as
electric motors, generators, transformers,
relays, lifting electromagnets, SQUIDs,
galvanometers, and magnetic recording
heads.

µ0 =
4π ×10−7 H / m ≈1.2566370614... ×10−6 N / A2 or T ⋅ m / A orWb / ( A ⋅ m ) orV ⋅ s / ( A ⋅ m)

in the SI system of units.
As a constant, it can also be defined
as a fundamental invariant quantity, and
is also one of three components that
defines free space through Maxwell’s
equations. In classical physics, free
space is a concept of electromagnetic
theory, corresponding to a theoretically
perfect vacuum and sometimes referred
to as the vacuum of free space, or as
classical vacuum, and is appropriately
viewed as a reference medium.

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Magnetic Core
A magnetic core is a piece of magnetic
material with a high magnetic
permeability used to confine and
guide magnetic fields in electrical,
electromechanical and magnetic devices
such as electromagnets, transformers,
electric motors, generators, inductors,
magnetic recording heads, and magnetic
assemblies. It is made of ferromagnetic
metal such as iron, or ferromagnetic
compounds such as ferrites. The high
permeability, relative to the surrounding
air, causes the magnetic field lines to
be concentrated in the core material.
The magnetic field is often created by
a current-carrying coil of wire around
the core.

Magnetic Core Memory
Magnetic-core memory was the
predominant form of random-access
computer memory for 20 years between
about 1955 and 1975. Such memory
is often just called core memory, or,
informally, core.

Magnetic Field
A magnetic field is a force field that
is created by moving electric charges
(electric currents) and magnetic dipoles,
and exerts a force on other nearby
moving charges and magnetic dipoles.
At any given point, it has a direction
and a magnitude (or strength), so it
is represented by a vector field. The
term is used for two distinct but closely
related fields denoted by the symbols
B and H, where, in the International
System of Units, H is measured in units
of amperes per meter and B is measured
in teslas or newtons per meter per
ampere. In a vacuum, B and H are the
same aside from units; but in a material
with a magnetization (denoted by the
symbol M), B is solenoidal (having no
divergence in its spatial dependence)
while H is irrotational (curl-free).

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Magnetic field intensity

Magnetism

Magnetic field intensity is the part of
the magnetic field in a material that
arises from an external source of current
and is not an intrinsic property of the
material itself. It is a vector quantity
denoted by the symbol H. The unit for
measurement of magnetic field intensity
is amperes per meter.

Magnetism is a class of physical
phenomena that are mediated by
magnetic fields. Electric currents and
the magnetic moments of elementary
particles give rise to a magnetic field,
which acts on other currents and
magnetic moments. The most familiar
effects occur in ferromagnetic materials,
which are strongly attracted by magnetic
fields and can be magnetized to become
permanent magnets, producing magnetic
fields themselves. Only a few substances
are ferromagnetic; the most common
ones are iron, nickel and cobalt and
their alloys. The prefix ferro- refers to
iron, because permanent magnetism was
first observed in lodestone, a form of
natural iron ore called magnetite, Fe3O4.

Magnetic Flux

M

The magnetic flux (often denoted Φ
or ΦB) through a surface is the surface
integral of the normal component of
the magnetic field B passing through
that surface. The SI unit of magnetic
flux is the weber (Wb) (in derived
units: volt-seconds), and the CGS unit
is the maxwell. Magnetic flux is usually
measured with a fluxmeter, which
contains measuring coils and electronics,
that evaluates the change of voltage
in the measuring coils to calculate the
magnetic flux.

Magnetization
Magnetic Moment
The magnetic moment of a magnet is a
quantity that determines the torque it
will experience in an external magnetic
field. A loop of electric current, a bar
magnet, an electron, a molecule, and a
planet all have magnetic moments.

Magnetization or magnetic polarization
is the vector field that expresses the
density of permanent or induced
magnetic dipole moments in a magnetic
material. The origin of the magnetic
moments responsible for magnetization
can be either microscopic electric
currents resulting from the motion
of electrons in atoms, or the spin

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of the electrons or the nuclei. Net
magnetization results from the response
of a material to an external magnetic
field, together with any unbalanced
magnetic dipole moments that may
be inherent in the material itself; for
example, in ferromagnets. Magnetization
is not always uniform within a body,
but rather varies between different
points. Magnetization also describes
how a material responds to an applied
magnetic field as well as the way the
material changes the magnetic field, and
can be used to calculate the forces that
result from those interactions. It can be
compared to electric polarization, which
is the measure of the corresponding
response of a material to an electric
field in electrostatics.

Magnetostatics
Magnetostatics is the study of magnetic
fields in systems where the currents are
steady (not changing with time). It is
the magnetic analogue of electrostatics,
where the charges are stationary. The
magnetization need not be static; the
equations of magnetostatics can be
used to predict fast magnetic switching
events that occur on time scales of
nanoseconds or less. Magnetostatics is
even a good approximation when the
currents are not static — as long as
the currents do not alternate rapidly.
Magnetostatics is widely used in
applications of micromagnetics such as
models of magnetic recording devices.
Magnetostatic focussing can be achieved
either by a permanent magnet or by
passing current through a coil of wire
whose axis coincides with the beam axis.

Magnetostriction
Magnetostriction (cf. electrostriction) is
a property of ferromagnetic materials
that causes them to change their shape
or dimensions during the process
of magnetization. The variation of
materials’ magnetization due to the
applied magnetic field changes the
magnetostrictive strain until reaching
its saturation value, λ.

Magnetron
A magnetron is a device to create
microwaves within the radio frequency
(rf) range from 0.3 to 300 GHz. In its
most popular application it is serving
as an oscillator in a microwave oven.
Besides that, magnetrons are used in
radar technique. This specific magnetron
is a strapped cooker magnetron.

Magnifying Transmitter
Tesla’s wireless research required
increasingly high voltages, and he
had reached the limit of the voltages

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M

he could generate within the space of
his New York lab. Between 1899 and
1900 he built a laboratory in Colorado
Springs and performed experiments on
wireless transmission there. He chose
this location because the polyphase
alternating current power distribution
system had been introduced there and
he had associates who were willing
to give him all the power he needed
without charging for it. The Colorado
Springs laboratory had one of the largest
Tesla coils ever built, which Tesla called
a “magnifying transmitter” as it was
intended to transmit power to a distant
receiver. With an input power of 300
kilowatts it could produce potentials
of the order of 10 million volts, at
frequencies of 50–150 kHz, creating
huge “lightning bolts” reportedly up
to 135 feet long. During experiments,
it caused an overload which set fire to
the alternator of the Colorado Springs
power company, destroying it, and Tesla
had to rebuild the alternator.

supplying services through user
telephone lines are terminated at the
MDF and distributed through the MDF
to equipment within the local exchange
e.g. repeaters and DSLAM. Cables to
intermediate distribution frames (IDF)
terminate at the MDF. Trunk cables may
terminate on the same MDF or on a
separate trunk main distribution frame
(TMDF).

Mainframe Computer
Mainframe computers (colloquially
referred to as “big iron”) are computers
used primarily by large organizations
for critical applications; bulk data
processing, such as census, industry
and consumer statistics, enterprise
resource planning; and transaction
processing. They are larger and have
more processing power than some other
classes of computers: minicomputers,
servers, workstations, and personal
computers.

Mains Electricity

Main Distribution Frame
A main distribution frame (MDF or
main frame) is a signal distribution
frame for connecting equipment (inside
plant) to cables and subscriber carrier
equipment (outside plant). The MDF
is a termination point within the local
telephone exchange where exchange
equipment and terminations of local
loops are connected by jumper wires
at the MDF. All cable copper pairs

Mains electricity is the general-purpose
alternating-current (AC) electric power
supply. Mains electricity is the form
of electrical power that is delivered to
homes and businesses, and it is the form
of electrical power that consumers use
when they plug kitchen appliances,
televisions and electric lamps into wall
sockets.

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standards. Physical compatibility of
receptacles may not ensure compatibility
of voltage, frequency, or connection to
earth ground.

Mains Hum
Mains hum, electric hum, or power
line hum is a sound associated with
alternating current at the frequency of
the mains electricity. The fundamental
frequency of this sound is usually 50 Hz
or 60 Hz, depending on the local powerline frequency. The sound often has
heavy harmonic content above 50–60 Hz.
Because of the presence of mains current
in mains-powered audio equipment as
well as ubiquitous AC electromagnetic
fields from nearby appliances and
wiring, 50/60 Hz electrical noise can
get into audio systems, and is heard as
mains hum from their speakers. Mains
hum may also be heard coming from
powerful electric power grid equipment
such as utility transformers, caused by
mechanical vibrations induced by the
powerful AC current in them.

Mains Power Systems

Manufacturing Engineering
Manufacturing Engineering is a
branch of professional engineering
concerned with the understanding and
application of Engineering Procedures in
Manufacturing Processes and Production
Methods. Manufacturing Engineering
requires the ability to plan the practices
of manufacturing; to research and to
develop tools, processes, machines
and equipments; and to integrate the
facilities and systems for producing
quality product with the optimum
expenditure of capital.

Mains electricity by country includes a
list of countries and territories, with the
plugs, voltages and frequencies they use
for providing electrical power to small
appliances and some major appliances.
Every country has differing rules
regarding distribution of electricity for
portable appliances and lighting. Voltage,
frequency, and plug type vary widely,
but large regions may use common
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Marginal Stability
A linear time-invariant system is
marginally stable if it is neither
asymptotically stable nor unstable.
Roughly speaking, a system is stable
if it always returns to and stays near a
particular state (called the steady state),
and is unstable if it goes farther and
farther away from any state, without
being bounded. A marginal system,
sometimes referred to as having neutral
stability, is between these two types:
when displaced, it does not return to
near a common steady state, nor does it
go away from where it started without
limit.

Marine Energy
M

Marine energy or marine power (also
sometimes referred to as ocean energy,
ocean power, or marine and hydrokinetic
energy) refers to the energy carried by
ocean waves, tides, salinity, and ocean
temperature differences. The movement
of water in the world’s oceans creates a
vast store of kinetic energy, or energy in
motion. This energy can be harnessed
to generate electricity to power homes,
transport and industries.

Maser
A maser (an acronym for “microwave
amplification by stimulated emission
of radiation”) is a device that produces
coherent electromagnetic waves through
amplification by stimulated emission.
The first maser was built by Charles
H. Townes, James P. Gordon, and H. J.
Zeiger at Columbia University in 1953.
Townes, Nikolay Basov and Alexander
Prokhorov were awarded the 1964 Nobel
Prize in Physics for theoretical work
leading to the maser. Masers are used as
the timekeeping device in atomic clocks,
and as extremely low-noise microwave
amplifiers in radio telescopes and deep
space spacecraft communication ground
stations.

Marx Generator
A Marx generator is an electrical circuit
first described by Erwin Otto Marx in
1924. Its purpose is to generate a highvoltage pulse from a low-voltage DC
supply. Marx generators are used in
high-energy physics experiments, as well
as to simulate the effects of lightning on
power-line gear and aviation equipment.
A bank of 36 Marx generators is used
by Sandia National Laboratories to
generate X-rays in their Z Machine.

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Mathematical Model
A mathematical model is a description
of a system using mathematical concepts
and language. The process of developing
a mathematical model is termed
mathematical modeling. Mathematical
models are used in the natural sciences
(such as physics, biology, Earth science,
meteorology) and engineering disciplines
(such as computer science, artificial
intelligence), as well as in the social
sciences (such as economics, psychology,
sociology, political science). Physicists,
engineers, statisticians, operations
research analysts, and economists use
mathematical models most extensively.
A model may help to explain a system
and to study the effects of different
components, and to make predictions
about behaviour.

Mathematics
Mathematics is the study of such topics
as quantity, structure, space, and change.
It has no generally accepted definition.
Mathematicians seek out patterns
and use them to formulate new
conjectures. Mathematicians resolve
the truth or falsity of conjectures by
mathematical proof. When mathematical
structures are good models of real
phenomena, then mathematical
reasoning can provide insight or
predictions about nature. Through the
use of abstraction and logic, mathematics
developed from counting, calculation,
measurement, and the systematic study
of the shapes and motions of physical
objects. Practical mathematics has been
a human activity from as far back as
written records exist. The research
required to solve mathematical problems
can take years or even centuries of
sustained inquiry.

Matrix (mathematics)
A matrix (plural: matrices) is a
rectangular array of numbers, symbols,
or expressions, arranged in rows and
columns. For example, the dimensions of
the matrix below are 2 × 3 (read “two
by three”), because there are two rows
and three columns:

 1 9 −13
 20 5 −6  .


The individual items in an m × n
matrix A, often denoted by ai,j, where
max i = m and max j = n, are called its
elements or entries. Provided that they
have the same size (each matrix has
the same number of rows and the same
number of columns as the other), two
matrices can be added or subtracted
element by element

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Maximum Prospective
short-circuit Current

1862 published an early form of the
equations, and first proposed that light
is an electromagnetic phenomenon.

The prospective short-circuit current
(PSCC), available fault current, or shortcircuit making current is the highest
electric current which can exist in a
particular electrical system under shortcircuit conditions. It is determined
by the voltage and impedance of the
supply system. It is of the order of a
few thousand amperes for a standard
domestic mains electrical installation,
but may be as low as a few milliamperes
in a separated extra-low voltage (SELV)
system or as high as hundreds of
thousands of amps in large industrial
power systems.

Maxwell’s equations
M

Maxwell’s equations are a set of partial
differential equations that, together
with the Lorentz force law, form the
foundation of classical electromagnetism,
classical optics, and electric circuits.
They underpin all electric, optical and
radio technologies, including power
generation, electric motors, wireless
communication, cameras, televisions,
computers etc. Maxwell’s equations
describe how electric and magnetic
fields are generated by charges,
currents, and changes of each other.
One important consequence of the
equations is that they demonstrate how
fluctuating electric and magnetic fields
propagate at the speed of light. Known
as electromagnetic radiation, these
waves may occur at various wavelengths
to produce a spectrum from radio waves
to γ-rays. The equations are named after
the physicist and mathematician James
Clerk Maxwell, who between 1861 and

Mean Free Path
The mean free path is the average
distance traveled by a moving particle
(such as an atom, a molecule, a photon)
between successive impacts (collisions),
which modify its direction or energy or
other particle properties.

Measurement
Measurement is the assignment of a
number to a characteristic of an object
or event, which can be compared with
other objects or events. The scope
and application of a measurement is
dependent on the context and discipline.
In the natural sciences and engineering,
measurements do not apply to nominal
properties of objects or events, which
is consistent with the guidelines of the
International vocabulary of metrology
published by the International Bureau
of Weights and Measures. However, in
other fields such as statistics as well
as the social and behavioral sciences,
measurements can have multiple levels,
which would include nominal, ordinal,
interval, and ratio scales.

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Medical Equipment
Mechanical Rectifier
A mechanical rectifier is a device for
converting alternating current (AC)
to direct current (DC) by means of
mechanically operated switches. The
best-known type is the commutator,
which is an integral part of a DC
dynamo, but before solid-state
devices became available, independent
mechanical rectifiers were used for
certain applications. Before the invention
of semiconductors, rectification at high
currents involved serious losses.

Mechatronics
Mechatronics is a multidisciplinary
field of science that includes a
combination of mechanical engineering,
electronics, computer engineering,
telecommunications engineering,
systems engineering and control
engineering. As technology advances,
the subfields of engineering multiply
and adapt. Mechatronics’ aim is a
design process that unifies these
subfields. Originally, mechatronics just
included the combination of mechanics
and electronics, therefore the word
is a combination of mechanics and
electronics; however, as technical systems
have become more and more complex
the definition has been broadened to
include more technical areas.

Medical equipment (also known as
armamentarium) is designed to aid in
the diagnosis, monitoring or treatment
of medical conditions.

Memistor
A memistor is a nanoelectric circuitry
element used in parallel computing
memory technology. Essentially, a
resistor with memory able to perform
logic operations and store information,
it is a three-terminal implementation of
the memristor. It is a possible future
technology replacing flash and DRAM.

Mendocino motor
The Mendocino motor is a solar-powered
magnetically levitated electric motor.
The motor consists of a four-,
five-, six- or eight-sided rotor block in
the middle of a shaft. The rotor block
has two sets of windings and a solar
cell attached to each side. The shaft
is positioned horizontally and has a
magnet at each end. The magnets on
the shaft provide levitation by repelling
magnets in a base under the motor. This
air friction bearing is required because
a Mendocino motor uses Lorentz force
without iron core. There is an additional
magnet that sits under the rotor block
and provides a magnetic field for the

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rotor. Other motors hide the base magnet
in a tube.

Mercury Vapor Lamp
A mercury-vapor lamp is a gas discharge
lamp that uses an electric arc through
vaporized mercury to produce light. The
arc discharge is generally confined to a
small fused quartz arc tube mounted
within a larger borosilicate glass bulb.
The outer bulb may be clear or coated
with a phosphor; in either case, the
outer bulb provides thermal insulation,
protection from the ultraviolet radiation
the light produces, and a convenient
mounting for the fused quartz arc tube.

Mesh
A mesh is a barrier made of connected
strands of metal, fiber, or other flexible
or ductile materials. A mesh is similar
to a web or a net in that it has many
attached or woven strands.

M

Mesh Analysis

Mercury-arc valve
A mercury-arc valve or mercury-vapor
rectifier or (UK) mercury-arc rectifier
is a type of electrical rectifier used
for converting high-voltage or highcurrent alternating current (AC) into
direct current (DC). It is a type of cold
cathode gas-filled tube, but is unusual
in that the cathode, instead of being
solid, is made from a pool of liquid
mercury and is therefore self-restoring.
As a result, mercury-arc valves were
much more rugged and long-lasting,
and could carry much higher currents
than most other types of gas discharge
tube.

Mesh analysis (or the mesh current
method) is a method that is used to
solve planar circuits for the currents
(and indirectly the voltages) at any place
in the electrical circuit. Planar circuits
are circuits that can be drawn on a plane
surface with no wires crossing each
other. A more general technique, called
loop analysis (with the corresponding
network variables called loop currents)
can be applied to any circuit, planar or
not. Mesh analysis and loop analysis
both make use of Kirchhoff’s voltage
law to arrive at a set of equations
guaranteed to be solvable if the circuit
has a solution. Mesh analysis is usually
easier to use when the circuit is planar,
compared to loop analysis.

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Mesh Networking
A mesh network is a local network
topology in which the infrastructure
nodes (i.e. bridges, switches and other
infrastructure devices) connect directly,
dynamically and non-hierarchically to
as many other nodes as possible and
cooperate with one another to efficiently
route data from/to clients. This lack of
dependency on one node allows for
every node to participate in the relay of
information. Mesh networks dynamically
self-organize and self-configure, which
can reduce installation overhead. The
ability to self-configure enables dynamic
distribution of workloads, particularly
in the event that a few nodes should
fail. This in turn contributes to faulttolerance and reduced maintenance
costs.

Metadyne
A metadyne is a direct current electrical
machine with two pairs of brushes. It
can be used as an amplifier or rotary

transformer. It is similar to a third brush
dynamo but has additional regulator or
“variator” windings. It is also similar
to an amplidyne except that the latter
has a compensating winding which
fully counteracts the effect of the flux
produced by the load current. The
technical description is “a cross-field
direct current machine designed to
utilize armature reaction”. A metadyne
can convert a constant-voltage input
into a constant-current, variable-voltage
output.

Metal Detector
A metal detector is an electronic
instrument which detects the presence
of metal nearby. Metal detectors are
useful for finding metal inclusions
hidden within objects, or metal objects
buried underground. They often consist
of a handheld unit with a sensor probe
which can be swept over the ground or
other objects.

If the sensor comes near a piece of metal
this is indicated by a changing tone
in earphones, or a needle moving on
an indicator. Usually the device gives
some indication of distance; the closer
the metal is, the higher the tone in the
earphone or the higher the needle goes.
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Another common type are stationary
“walk through” metal detectors used
for security screening at access points
in prisons, courthouses, and airports
to detect concealed metal weapons on
a person’s body.

Metal Rectifier
A metal rectifier is an early type of
semiconductor rectifier in which the
semiconductor is copper oxide or
selenium. They were used in power
applications to convert alternating
current to direct current in devices
such as radios and battery chargers.
Westinghouse Electric was a major
manufacturer of these rectifiers since
the late 1920s, under the trade name
Westector (now used as a trade name
for an overcurrent trip device by
Westinghouse Nuclear).
M

Micro combined heat and
power
Micro combined heat and power or
micro-CHP or mCHP is an extension
of the idea of cogeneration to the single/
multi family home or small office
building in the range of up to 50 kW.
Local generation has the potential for
a higher efficiency than traditional
grid-level generators since it lacks the
8-10% energy losses from transporting
electricity over long distances. It also
lacks the 10–15% energy losses from
heat transfer in district heating networks
due to the difference between the
thermal energy carrier (hot water) and
the colder external environment. The
most common systems use natural gas
as their primary energy source and emit
carbon dioxide.

Microcontroller

Metalworking
Metalworking is the process of working
with metals to create individual parts,
assemblies, or large-scale structures. The
term covers a wide range of work from
large ships and bridges to precise engine
parts and delicate jewelry. It therefore
includes a correspondingly wide range
of skills, processes, and tools.

A microcontroller (or MCU for
microcontroller unit) is a small computer
on a single integrated circuit. In modern
terminology, it is similar to, but less
sophisticated than, a system on a
chip or SoC; an SoC may include a
microcontroller as one of its components.
A microcontroller contains one or more
CPUs (processor cores) along with
memory and programmable input/
output peripherals. Program memory
in the form of ferroelectric RAM, NOR
flash or OTP ROM is also often included
on chip, as well as a small amount of
RAM. Microcontrollers are designed for
embedded applications, in contrast to
the microprocessors used in personal
computers or other general purpose
applications consisting of various
discrete chips.

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capacitors, inductors, resistors, diodes
and (naturally) insulators and conductors
can all be found in microelectronic
devices. Unique wiring techniques
such as wire bonding are also often
used in microelectronics because of the
unusually small size of the components,
leads and pads. This technique requires
specialized equipment and is expensive.

Microelectromechanical
Systems
Microelectromechanical systems
(MEMS, also written as microelectro-mechanical, Micro Electro
Mechanical or microelectronic and
microelectromechanical systems and
the related micromechatronics) is the
technology of microscopic devices,
particularly those with moving parts.
It merges at the nano-scale into
nanoelectromechanical systems (NEMS)
and nanotechnology. MEMS are also
referred to as micromachines in Japan,
or micro systems technology (MST) in
Europe.

Microelectronics
Microelectronics is a subfield of
electronics. As the name suggests,
microelectronics relates to the study
and manufacture (or microfabrication)
of very small electronic designs and
components. Usually, but not always,
this means micrometre-scale or smaller.
These devices are typically made
from semiconductor materials. Many
components of normal electronic design
are available in a microelectronic
equivalent. These include transistors,

Microfabrication
Microfabrication is the process of
fabricating miniature structures
of micrometre scales and smaller.
Historically, the earliest microfabrication
processes were used for integrated
circuit fabrication, also known as
“semiconductor manufacturing”
or
“semiconductor
device
fabrication”. In the last two decades
microelectromechanical systems
(MEMS), microsystems (European
usage), micromachines ( Japanese
terminology) and their subfields,
microfluidics/lab-on-a-chip, optical
MEMS (also called MOEMS), RF MEMS,
PowerMEMS, BioMEMS and their
extension into nanoscale (for example
NEMS, for nano electro mechanical
systems) have re-used, adapted or
extended microfabrication methods.
Flat-panel displays and solar cells are
also using similar techniques.

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Microgeneration

M

Microgeneration is the small-scale
generation of heat and electric power
by individuals, small businesses and
communities to meet their own needs,
as alternatives or supplements to
traditional centralized grid-connected
power. Although this may be motivated
by practical considerations, such as
unreliable grid power or long distance
from the electrical grid, the term is mainly
used currently for environmentally
conscious approaches that aspire to
zero or low-carbon footprints or cost
reduction. It differs from micropower
in that it is principally concerned with
fixed power plants rather than for use
with mobile devices.

Microphone
A microphone is a transducer that
converts sound into an electrical signal.
Microphones are used in many
applications such as telephones, hearing
aids, public address systems for concert
halls and public events, motion picture
production, live and recorded audio
engineering, sound recording, two-way
radios, megaphones, radio and television
broadcasting, and in computers for
recording voice, speech recognition,
VoIP, and for non-acoustic purposes such
as ultrasonic sensors or knock sensors.

Microprocessor
A microprocessor is a computer
processor which incorporates the
functions of a computer ’s central
processing unit (CPU) on a single
integrated circuit (IC), or at most a few
integrated circuits. The microprocessor
is a multipurpose, clock driven, register
based, digital-integrated circuit which
accepts binary data as input, processes
it according to instructions stored in
its memory, and provides results as
output. Microprocessors contain both
combinational logic and sequential
digital logic. Microprocessors operate
on numbers and symbols represented
in the binary numeral system.

Microprocessor unit
A computer processor unit on a single
integrated circuit (IC) that performs
major data processing work.

Microwave
Microwaves are a form of electromagnetic
radiation with wavelengths ranging
from one meter to one millimeter; with

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frequencies between 300 MHz (100 cm)
and 300 GHz (0.1 cm). Different sources
define different frequency ranges as
microwaves; the above broad definition
includes both UHF and EHF (millimeter
wave) bands. A more common definition
in radio engineering is the range
between 1 and 100 GHz (300 and 3 mm).
In all cases, microwaves include the
entire SHF band (3 to 30 GHz, or 10 to
1 cm) at minimum. Frequencies in the
microwave range are often referred to
by their IEEE radar band designations:
S, C, X, Ku, K, or Ka band, or by similar
NATO or EU designations.

Milliampere
A measure for small electric currents i.e.
one thousandth of an ampere.

M

Millihenry
A unit of inductance equal to one
thousandth of a henry.

Microwave Oven
A microwave oven (also commonly
referred to as a microwave) is an electric
oven that heats and cooks food by
exposing it to electromagnetic radiation
in the microwave frequency range. This
induces polar molecules in the food to
rotate and produce thermal energy in
a process known as dielectric heating.
Microwave ovens heat foods quickly and
efficiently because excitation is fairly
uniform in the outer 25–38 mm (1–1.5
inches) of a homogeneous, high water
content food item; food is more evenly
heated throughout than generally occurs
in other cooking techniques.

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Milliwatt
A unit of power equal to one thousandth
of a watt.

Millman’s theorem
Millman’s theorem (or the parallel
generator theorem) is a method to
simplify the solution of a circuit.
Specifically, Millman’s theorem is used
to compute the voltage at the ends of
a circuit made up of only branches in
parallel.

Mineral-insulated copperclad cable

M

Mineral-insulated copper-clad cable
is a variety of electrical cable made
from copper conductors inside a
copper sheath, insulated by inorganic
magnesium oxide powder. The name
is often abbreviated to MICC or MI
cable, and colloquially known as pyro
(because the original manufacturer and
vendor for this product in the UK was
a company called Pyrotenax). A similar
product sheathed with metals other than
copper is called mineral insulated metal
sheathed (MIMS) cable.

Modbus
Modbus is a serial communications
protocol originally published by Modicon
(now Schneider Electric) in 1979 for use
with its programmable logic controllers
(PLCs). Modbus has become a de facto
standard communication protocol and
is now a commonly available means of
connecting industrial electronic devices.

Model Predictive Control
Model predictive control (MPC) is an
advanced method of process control that
has been in use in the process industries
in chemical plants and oil refineries since
the 1980s. In recent years it has also
been used in power system balancing
models. Model predictive controllers
rely on dynamic models of the process,
most often linear empirical models
obtained by system identification. The
main advantage of MPC is the fact
that it allows the current timeslot to
be optimized, while keeping future
timeslots in account. This is achieved
by optimizing a finite time-horizon, but
only implementing the current timeslot
and then optimizing again, repeatedly,
thus differing from LQR. Also MPC
has the ability to anticipate future
events and can take control actions
accordingly. PID controllers do not have
this predictive ability. MPC is nearly
universally implemented as a digital
control, although there is research into
achieving faster response times with
specially designed analog circuitry.

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Modem

Modulation Transformer

A modem (modulator–demodulator)
is a network hardware device that
modulates one or more carrier wave
signals to encode digital information for
transmission and demodulates signals
to decode the transmitted information.
The goal is to produce a signal that
can be transmitted easily and decoded
to reproduce the original digital data.
Modems can be used with any means of
transmitting analog signals, from lightemitting diodes to radio. A common type
of modem is one that turns the digital
data of a computer into modulated
electrical signal for transmission over
telephone lines and demodulated by
another modem at the receiver side to
recover the digital data.

A modulation transformer is an audiofrequency transformer that forms a
major part of most AM transmitters.
The primary winding of a modulation
transformer is fed by an audio amplifier
that has about 1/2 of the rated input
power of the transmitter’s final amplifier
stage. The secondary winding is in
series with the power supply of that
final radio-frequency amplifier stage,
thereby allowing the audio signal to
lower and raise the instantaneous DC
supply voltage of the power amplifier
(PA) tube or transistor. Considering
that the PA device is operated as a
class-C amplifier, i.e. as a switch, the
modulation transformer is responsible
for the amplitude modulation (AM) of
the transmitter.
M

Monoscope
Modulation
Modulation is the process of varying
one or more properties of a periodic
waveform, called the carrier signal,
with a modulating signal that typically
contains information to be transmitted.
Most radio systems in the 20th century
used frequency modulation (FM) or
amplitude modulation (AM) to make
the carrier carry the radio broadcast.

A monoscope was a special form of
video camera tube which displayed a
single still video image. The image was
built into the tube, hence the name.
The tube resembled a small cathode
ray tube (CRT). Monoscopes were used
beginning in the 1950s to generate TV
test patterns and station logos. This
type of test card generation system was
technologically obsolete by the 1980s.

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small set of punctuation and procedural
signals (prosigns) as standardized
sequences of short and long signals
called “dots” and “dashes”, or “dits”
and “dahs”, as in amateur radio practice.
Because many non-English natural
languages use more than the 26 Roman
letters, extensions to the Morse alphabet
exist for those languages.

Moore’s law

M

Moore’s law is the observation that
the number of transistors in a dense
integrated circuit doubles approximately
every two years. The observation is
named after Gordon Moore, the cofounder of Fairchild Semiconductor
and Intel, whose 1965 paper described
a doubling every year in the number
of components per integrated circuit,
and projected this rate of growth would
continue for at least another decade. In
1975, looking forward to the next decade,
he revised the forecast to doubling
every two years. The period is often
quoted as 18 months because of Intel
executive David House, who predicted
that chip performance would double
every 18 months (being a combination
of the effect of more transistors and the
transistors being faster).

Metal oxide semiconductor
device
Transistors with three layers – a metal
conductor, an insulating silicon layer,
and a semiconductor silicon layer.

Morse code
Morse code is a method of transmitting
text information as a series of on-off
tones, lights, or clicks that can be
directly understood by a skilled listener
or observer without special equipment.
It is named for Samuel F. B. Morse,
an inventor of the telegraph. The
International Morse Code encodes the
ISO basic Latin alphabet, some extra
Latin letters, the Arabic numerals and a

MOSFET
The metal-oxide-semiconductor fieldeffect transistor (MOSFET, MOS-FET,
or MOS FET) is a type of field-effect
transistor (FET), most commonly
fabricated by the controlled oxidation of
silicon. It has an insulated gate, whose

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voltage determines the conductivity
of the device. This ability to change
conductivity with the amount of applied
voltage can be used for amplifying or
switching electronic signals. A metalinsulator-semiconductor field-effect
transistor or MISFET is a term almost
synonymous with MOSFET. Another
synonym is IGFET for insulated-gate
field-effect transistor.

Motor controller
A motor controller is a device or group
of devices that serves to govern in some
predetermined manner the performance
of an electric motor. A motor controller
might include a manual or automatic
means for starting and stopping the
motor, selecting forward or reverse
rotation, selecting and regulating the
speed, regulating or limiting the torque,
and protecting against overloads and
faults.

Motor Soft Starter

Motion Control
Motion control is a sub-field of
automation, encompassing the systems
or sub-systems involved in moving parts
of machines in a controlled manner. The
main components involved typically
include a motion controller, an energy
amplifier, and one or more prime
movers or actuators. Motion control
may be open loop or closed loop. In
open loop systems, the controller sends
a command through the amplifier to
the prime mover or actuator, and does
not know if the desired motion was
actually achieved. Typical systems
include stepper motor or fan control.
For tighter control with more precision,
a measuring device may be added to the
system (usually near the end motion).
When the measurement is converted to a
signal that is sent back to the controller,
and the controller compensates for any
error, it becomes a Closed loop System.

A motor soft starter is a device used
with AC electrical motors to temporarily
reduce the load and torque in the power
train and electric current surge of the
motor during start-up. This reduces
the mechanical stress on the motor
and shaft, as well as the electrodynamic
stresses on the attached power cables
and electrical distribution network,
extending the lifespan of the system.

MRI
Magnetic resonance imaging is a medical
imaging technique used in radiology to
form pictures of the anatomy and the
physiological processes of the body in

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both health and disease. MRI scanners
use strong magnetic fields, electric
field gradients, and radio waves to
generate images of the organs in the
body. MRI does not involve X-rays
and the use of ionizing radiation,
which distinguishes it from CT or CAT
scans. Magnetic resonance imaging is a
medical application of nuclear magnetic
resonance (NMR). NMR can also be used
for imaging in other NMR applications
such as NMR spectroscopy.

example when monitoring a rapidly
varying value.

Multics

M

Multics (Multiplexed Information and
Computing Service) is an influential early
time-sharing operating system, based
around the concept of a single-level
memory. Virtually all modern operating
systems were heavily influenced by
Multics, often through Unix, which
had been created by the people who
had worked on Multics—either directly
(Linux, macOS) or indirectly (Microsoft
Windows NT).

Multimeter
A multimeter or a multitester,
also known as a VOM (volt-ohmmilliammeter), is an electronic
measuring instrument that combines
several measurement functions in one
unit. A typical multimeter can measure
voltage, current, and resistance. Analog
multimeters use a microammeter with
a moving pointer to display readings.
Digital multimeters (DMM, DVOM)
have a numeric display, and may also
show a graphical bar representing the
measured value. Digital multimeters are
now far more common due to their cost
and precision, but analog multimeters
are still preferable in some cases, for

Mutual conductance
The electrical characteristic relating the
current through the output of a device to
the voltage across the input of a device.

Mutual inductance
Mutual inductance is the main operating
principle of generators, motors and
transformers. Any electrical device
having components that tend to interact
with another magnetic field also follows
the same principle. The interaction is
usually brought about by a mutual
induction where the current flowing
in one coil generates a voltage in a
secondary coil.

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Nn
n-p-n transistor
NAK signal

The NPN transistor amplifies the weak
signal enter into the base and produces
strong amplify signals at the collector
end.

NAK is an abbreviation for negative
acknowledgment or not acknowledged.
It is a signal used in digital
communications to ensure that data
is received with a minimum of errors.
Sometimes the NAK signal is called REJ
(for rejection or rejected). An alternative
signal is ARQ (automatic request for
retransmission).

N

n-type semiconductor
An n-type semiconductor is an intrinsic
semiconductor doped with phosphorus
(P), arsenic (As), or antimony (Sb) as an
impurity. Silicon of Group IV has four
valence electrons and phosphorus of
Group V has five valence electrons. If a
small amount of phosphorus is added to
a pure silicon crystal, one of the valence
electrons of phosphorus becomes free
to move around (free electron) as a
surplus electron. When this free electron
is attracted to the “+” electrode and
moves, current flows.

Nameplate Capacity
Nameplate capacity, also known as
the rated capacity, nominal capacity,
installed capacity, or maximum effect, is
the intended full-load sustained output
of a facility such as a power plant, a
chemical plant, fuel plant, metal refinery,
mine, and many others. Nameplate
capacity is the number registered with
authorities for classifying the power
output of a power station usually
expressed in megawatts (MW).

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Nanoceramic

Nanodevice

The term nanoceramics refers to
materials fabricated from ultrafine
particles, less than 100 nm in diameter,
and are classified as inorganic, heat
resistant, non-metallic solids.

A nanodevice is a device with at least
one overall dimension in the nanoscale,
or comprising one or more nanoscale
components essential to its operation.

N

Nanocircuitry
Nanocircuits are electrical circuits
operating on the nanometer scale. This
is well into the quantum realm, where
quantum mechanical effects become
very important. One nanometer is equal
to 10−9 meters or a row of 10 hydrogen
atoms. With such progressively smaller
circuits, more can be fitted on a
computer chip.

Nanoelectromechanical
systems
Nanoelectromechanical systems (NEMS)
are a class of devices integrating
electrical and mechanical functionality
on the nanoscale.

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Nanoelectronics
Nanoelectronics refers to the use
of nanotechnology in electronic
components. The term covers a diverse
set of devices and materials, with the
common characteristic that they are so
small that inter-atomic interactions and
quantum mechanical properties need to
be studied extensively.

Nanoinverter
A nanoinverter, also referred as nano
inverter or solar nano inverter, converts
direct current (DC) from a single solar
cell or small solar panel to alternating
current (AC). Nanoinverters contrast
with microinverter devices, which are
connected to larger than 100 Watt solar
panels.

Nanoengineering
Nanoengineering is the practice of
engineering on the nanoscale. It derives
its name from the nanometre, a unit of
measurement equalling one billionth of
a meter.
Nanoengineering is largely a
synonym for nanotechnology, but
emphasizes the engineering rather than
the pure science aspects of the field.

Nanoinverters have several
advantages over microinverters.
The main advantage is that, even
small amounts of shading, debris
or snow lines in any one solar cell,
or a smaller panel failure, does not
disproportionately reduce the output of
an entire larger panel. Each nanoinverter
obtains optimum power by performing
maximum power point tracking for its
connected panel.

Nanoimprint lithography

Nanofabrication
Nanofabrication is the design and
manufacture of devices with dimensions
measured in nanometers. One
nanometer is 10 -9 meter, or a millionth
of a millimeter. Nanofabrication is of
interest to computer engineers because
it opens the door to super-high-density
microprocessor s and memory chips.

Nanoimprint lithography (NIL) is a
method of fabricating nanometer scale
patterns. It is a simple nanolithography
process with low cost, high throughput
and high resolution. It creates patterns
by mechanical deformation of imprint
resist and subsequent processes.

Nanomotor
A nanomotor is a molecular or nanoscale
device capable of converting energy into
movement. It can typically generate

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forces on the order of piconewtons.

dimensions in the volume of an object
which are on the nanoscale.

Nanorod
Nanorods are one morphology of
nanoscale objects. Each of their
dimensions range from 1–100 nm.
They may be synthesized from metals
or semiconducting materials. Standard
aspect ratios (length divided by width)
are 3-5. Nanorods are produced by
direct chemical synthesis.

N

Nanotechnology
Nanotechnology is manipulation
of matter on an atomic, molecular,
and supramolecular scale. The
earliest, widespread description
of nanotechnology referred to the
particular technological goal of precisely
manipulating atoms and molecules for
fabrication of macroscale products,
also now referred to as molecular
nanotechnology. A more generalized
description of nanotechnology was
subsequently established by the
National Nanotechnology Initiative,
which defines nanotechnology as the
manipulation of matter with at least
one dimension sized from 1 to 100
nanometers.

National Electric Code
Nanostructure
A nanostructure is a structure
of intermediate size between
microscopic
and
molecular
structures. Nanostructural detail
is microstructure at nanoscale. In
describing nanostructures, it is necessary
to differentiate between the number of

The National Electrical Code (NEC),
or NFPA 70, is a regionally adoptable
standard for the safe installation of
electrical wiring and equipment in the
United States. It is part of the National
Fire Codes series published by the
National Fire Protection Association
(NFPA), a private trade association.
Despite the use of the term “national”,

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it is not a federal law. It is typically
adopted by states and municipalities
in an effort to standardize their
enforcement of safe electrical practices.
In some cases, the NEC is amended,
altered and may even be rejected in lieu
of regional regulations as voted on by
local governing bodies.

account for 360,000 American jobs in
more than 7,000 facilities in every state.
Their industry produces $106 billion
shipments of electrical equipment and
medical imaging technologies per year
with $36 billion exports. NEMA also
has offices in Mexico City.

Natural Gas

National Electrical
Manufacturers Association
(NEMA)
The National Electrical Manufacturers
Association (NEMA) is the largest trade
association of electrical equipment
manufacturers in the United States. It
was founded in 1926 and maintains
its headquarters in Rosslyn, Virginia,
just outside Washington, D.C. Its
approximately 350 member companies
manufacture products used in the
generation, transmission, distribution,
control, and end use of electricity. These
products are used in utility, industrial,
commercial, institutional, and residential
applications. The association’s Medical
Imaging & Technology Alliance (MITA)
division represents manufacturers of
cutting-edge medical diagnostic imaging
equipment including MRI, CT, x-ray,
and ultrasound products. Other major
end markets include building systems,
electrical infrastructure, industrial
systems, lighting systems and utility
systems. Their combined industries

Natural gas is a naturally occurring also
come out bumhydrocarbon gas mixture
consisting primarily of methane, but
commonly including varying amounts
of other higher alkanes, and sometimes
a small percentage of carbon dioxide,
nitrogen, hydrogen sulfide, or helium. It
is formed when layers of decomposing
plant and animal matter are exposed
to intense heat and pressure under
the surface of the Earth over millions
of years. The energy that the plants
originally obtained from the sun is
stored in the form of chemical bonds
in the gas.

Negative Feedback
Negative feedback (or balancing
feedback) occurs when some function
of the output of a system, process, or
mechanism is fed back in a manner that
tends to reduce the fluctuations in the
output, whether caused by changes in
the input or by other disturbances.

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to lead to instability via exponential
growth, oscillation or chaotic behavior,
negative feedback generally promotes
stability. Negative feedback tends to
promote a settling to equilibrium, and
reduces the effects of perturbations.
Negative feedback loops in which just
the right amount of correction is applied
with optimum timing can be very stable,
accurate, and responsive.

Negative Resistance
Negative resistance (NR) is a property
of some electrical circuits and devices in
which an increase in voltageacross the
device’s terminals results in a decrease
in electric current through it.

N

Mountain Institute and environmentalist
Amory Lovins in 1985, within the article,
“Saving Gigabucks with Negawatts,”
where he argued that utility customers
don’t want kilowatt-hours of electricity;
they want energy services such as hot
showers, cold beer, lit rooms, and
spinning shafts, which can come more
cheaply if electricity is used more
efficiently. Lovins felt an international
behavioral change was necessary in
order to decrease countries’ dependence
on excessive amounts of energy. The
concept of a negawatt could influence
a behavioral change in consumers by
encouraging them to think about the
energy that they spend.

This is in contrast to an ordinary
resistor in which an increase of applied
voltage causes a proportional increase
in current due to Ohm’s law, resulting
in a positive resistance. While a positive
resistance consumes power from current
passing through it, a negative resistance
produces power. Under certain
conditions it can increase the power of
an electrical signal, amplifyingit.

Nelson River Bipole

Negawatt Power
Negawatt power is a theoretical unit
of power representing an amount of
electrical power (measured in watts)
saved. The energy saved is a direct result
of energy conservation or increased
energy efficiency. The term was coined
by the chief scientist of the Rocky

The Nelson River DC Transmission
System, also known as the Manitoba
Bipole, is an electric power transmission
system of two high voltage, direct current
lines in Manitoba, Canada, operated by
Manitoba Hydro as part of the Nelson
River Hydroelectric Project. It is now
recorded on the list of IEEE Milestones
in electrical engineering. Several records
have been broken by successive phases
of the project, including the largest (and
last) mercury-arc valves, the highest DC
transmission voltage and the first use of
water-cooledthyristor valves in HVDC.

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2,000 small shops producing neon signs
by 1940. In addition to signage, neon
lighting is used frequently by artists and
architects, and (in a modified form) in
plasma display panels and televisions.
The signage industry has declined in the
past several decades, and cities are now
concerned with preserving and restoring
their antique neon signs.

Neodymium magnets
A neodymium magnet (also known as
NdFeB, NIB or Neo magnet), the most
widely used type of rare-earth magnet,
is a permanent magnet made from an
alloy of neodymium, iron and boron to
form the Nd2Fe14B tetragonal crystalline
structure. Developed independently in
1982 by General Motors and Sumitomo
Special Metals, neodymium magnets are
the strongest type of permanent magnet
commercially available. They have
replaced other types of magnets in the
many applications in modern products
that require strong permanent magnets,
such as motors in cordless tools, hard
disk drives and magnetic fasteners.

Neon sign
Neon signs are electric signs lighted by
long luminous gas-discharge tubes that
contain rarefied neon or other gases.
They are the most common use for neon
lighting, which was first demonstrated
in a modern form in December 1910
by Georges Claude at the Paris Motor
Show. While they are used worldwide,
neon signs were popular in the United
States from about 1920–1960. The
installations in Times Square, many
originally designed by Douglas Leigh,
were famed, and there were nearly

N

Neon-sign transformer
A neon-sign transformer (NST) is a
transformer made for the purpose of
powering a neon sign. They convert
line voltage from the 120-347 V up to
high voltages, in the range of 2 to 15
kV. These transformers supply between
18-30 mA; 60 mA on special order. A
more general designation would be
“luminous tube transformer”, because
many other gases are used in luminous
gas discharge tubes.

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Network Protector

Net Metering

N

Net metering (or net energy metering,
NEM) allows consumers who generate
some or all of their own electricity to
use that electricity anytime, instead of
when it is generated. This is particularly
important with wind and solar, which
are non-dispatchable. Monthly net
metering allows consumers to use
solar power generated during the day
at night, or wind from a windy day
later in the month. Annual net metering
rolls over a net kilowatt credit to the
following month, allowing solar power
that was generated in July to be used in
December, or wind power from March
in August.

Network cable
Networking cables are networking
hardware used to connect one network
device to other network devices or to
connect two or more computers to
share printers, scanners etc. Different
types of network cables, such as coaxial
cable, optical fiber cable, and twisted
pair cables, are used depending on
the network’s physical layer, topology,
and size. The devices can be separated
by a few meters (e.g. via Ethernet) or
nearly unlimited distances (e.g. via the
interconnections of the Internet).

A network protector is a type of electric
protective device used in electricity
distribution systems. The network
protector automatically disconnect its
associated distribution transformer from
the secondary network when the power
starts flowing in reverse direction.
Network protectors are used on both
spot networks and grid networks.
The secondary grid system improves
continuity of service for customers, since
multiple sources are available to supply
the load; a fault with any one supply is
automatically isolated by the network
protector and does not interrupt service
from the other sources. Secondary grids
are often used in downtown areas of
cities where there are many customers
in a small area.

Neural Networks
Artificial neural networks (ANNs) or
connectionist systems are computing
systems vaguely inspired by the
biological neural networks that
constitute animal brains. Such systems
“learn” (i.e. progressively improve
performance on) tasks by considering
examples, generally without taskspecific programming. For example,
in image recognition, they might learn
to identify images that contain cats by
analyzing example images that have
been manually labeled as “cat” or “no

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meet. Without any further knowledge,
it is easy to establish how to find a
node by using Ohm’s Law: V=IR. When
looking at circuit schematics, ideal wires
have a resistance of zero. Since it can be
assumed that there is no change in the
potential across any part of the wire, all
of the wire in between any components
in a circuit is considered part of the
same node.

cat” and using the results to identify cats
in other images. They do this without
any a priori knowledge about cats, e.g.,
that they have fur, tails, whiskers and
cat-like faces. Instead, they evolve their
own set of relevant characteristics from
the learning material that they process.

Voltage = Current * Resistance

Nodal Analysis
In electric circuits analysis, nodal
analysis, node-voltage analysis, or the
branch current method is a method
of determining the voltage (potential
difference) between “nodes” (points
where elements or branches connect)
in an electrical circuit in terms of the
branch currents.

Node (circuits)
Node, refers to any point on a circuit
where two or more circuit elements

since voltage is a measure of potential
difference, the voltage between any two
parts of the same node is:
Vab= (Current) * 0
So at any two points on the same
branch of the circuit, the change in
potential difference is 0. Therefore,
throughout the entire node the voltage
is the same.

Noise Cancelling
Noise cancellation, or active noise
reduction (ANR), is a method for
reducing unwanted sound by the
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of a cable or other form of
transmission line.

addition of a second sound specifically
designed to cancel the first.

Noise Reduction

N

Noise reduction is the process of
removing noise from a signal. All
recording devices, both analog and
digital, have traits that make them
susceptible to noise. Noise can be
random or white noise with no
coherence, or coherent noise introduced
by the device’s mechanism or processing
algorithms.
In electronic recording devices,
a major form of noise is hiss caused
by random electrons that, heavily
influenced by heat, stray from their
designated path. These stray electrons
influence the voltage of the output
signal and thus create detectable noise.

Nominal Impedance
Nominal impedance in electrical
engineering and audio engineering refers
to the approximate designed impedance
of an electrical circuit or device. The
term is applied in a number of different
fields, most often being encountered in
respect of:
►

The nominal value of the
characteristic impedance

►

The nominal value of the input,
output or image impedance of
a port of a network, especially
a network intended for use
with a transmission line,
such as filters, equalisers and
amplifiers.

►

The nominal value of the input
impedance of a radio frequency
antenna

The actual impedance may vary
quite considerably from the nominal
figure with changes in frequency. In the
case of cables and other transmission
lines, there is also variation along the
length of the cable, if it is not properly
terminated.

Nonlinear Control
Nonlinear control theory is the area of
control theory which deals with systems
that are nonlinear, time-variant, or both.
Control theory is an interdisciplinary
branch of engineering and mathematics
that is concerned with the behavior of
dynamical systems with inputs, and
how to modify the output by changes
in the input using feedback. The system
to be controlled is called the “plant”. In
order to make the output of a system
follow a desired reference signal a
controller is designed which compares

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the output of the plant to the desired
output, and provides feedback to the
plant to modify the output to bring it
closer to the desired output.

Nonode
A nonode is a type of thermionic valve
that has nine active electrodes. The term
most commonly applies to a seven-grid
vacuum tube, also sometimes called an
enneode.

Norton’s theorem
Norton’s theorem states that all
linear circuits can be simplified to an
equivalent circuit with a single current
source in parallel with a single resistor
connected to a load.

used in Raman spectroscopy, live sound
reproduction (public address systems,
or PA systems) and in instrument
amplifiers (especially amplifiers or
preamplifiers for acoustic instruments
such as acoustic guitar, mandolin, bass
instrument amplifier, etc.) to reduce or
prevent audio feedback, while having
little noticeable effect on the rest of
the frequency spectrum (electronic or
software filters). Other names include
‘band limit filter’, ‘T-notch filter’, ‘bandelimination filter ’, and ‘band-reject
filter’.

NTSC
NTSC, named after the National
Television System Committee, is the
analog television system that is used
in North America, and until digital
conversion was used in most of the
Americas (except Brazil, Argentina,
Paraguay, Uruguay, and French Guiana);
Myanmar; South Korea; Taiwan;
Philippines, Japan; and some Pacific
island nations and territories (see map).

Notch Filter
A band-stop filter or band-rejection filter
is a filter that passes most frequencies
unaltered, but attenuates those in a
specific range to very low levels. It is
the opposite of a band-pass filter. A
notch filter is a band-stop filter with a
narrow stopband (high Q factor).
Narrow notch filters (optical) are

Nuclear Power
Nuclear power is the use of nuclear
reactions that release nuclear energy to
generate heat, which most frequently is
then used in steam turbines to produce
electricity in a nuclear power plant. The

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term includes nuclear fission, nuclear
decay and nuclear fusion. Presently, the
nuclear fission of elements in the actinide
series of the periodic table produce
the vast majority of nuclear energy in
the direct service of humankind, with
nuclear decay processes, primarily in
the form of geothermal energy, and
radioisotope thermoelectric generators,
in niche uses making up the rest.

Numerical Control

N

The nuvistor is a type of vacuum tube
announced by RCA in 1959. Most
nuvistors are basically thimble-shaped,
but somewhat smaller than a thimble,
and much smaller than conventional
tubes of the day, almost approaching
the compactness of early discrete
transistor casings. Triodes and a few
tetrodes were made. The tube is made
entirely of metal and ceramic. Making
nuvistors requires special equipment,
since there is no intubation to pump
gases out of the envelope. Instead, the
entire structure is assembled, inserted
into its metal envelope, sealed and
processed in a large vacuum chamber
with simple robotic devices.

Nuvistor
The nuvistor is a type of vacuum tube
announced by RCA in 1959. Most

nuvistors are basically thimble-shaped,
but somewhat smaller than a thimble,
and much smaller than conventional
tubes of the day, almost approaching
the compactness of early discrete
transistor casings. Triodes and a few
tetrodes were made. The tube is made
entirely of metal and ceramic. Making
nuvistors requires special equipment,
since there is no intubation to pump
gases out of the envelope. Instead, the
entire structure is assembled, inserted
into its metal envelope, sealed and
processed in a large vacuum chamber
with simple robotic devices.

Nyquist Frequency
The Nyquist frequency, named after
electronic engineer Harry Nyquist, is
half of the sampling rate of a discrete
signal processing system. It is sometimes
known as the folding frequency of
a sampling system. An example of
folding is depicted in Figure 1, where
fs is the sampling rate and 0.5 fs is the
corresponding Nyquist frequency. The
black dot plotted at 0.6 fs represents the
amplitude and frequency of a sinusoidal
function whose frequency is 60% of the
sample-rate (fs). The other three dots
indicate the frequencies and amplitudes
of three other sinusoids that would

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produce the same set of samples as
the actual sinusoid that was sampled.
The symmetry about 0.5 fs is referred
to as folding.

Nyquist stability Criterion
The Nyquist stability criterion,
discovered by Swedish-American
electrical engineer Harry Nyquist at
Bell Telephone Laboratories in 1932, is
a graphical technique for determining
the stability of a dynamical system.
Because it only looks at the Nyquist
plot of the open loop systems, it can
be applied without explicitly computing
the poles and zeros of either the closedloop or open-loop system (although the
number of each type of right-half-plane
singularities must be known). As a result,

it can be applied to systems defined by
non-rational functions, such as systems
with delays. In contrast to Bode plots, it
can handle transfer functions with right
half-plane singularities. In addition,
there is a natural generalization to more
complex systems with multiple inputs
and multiple outputs, such as control
systems for airplanes.

N

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Oo

Observability

Object code
Object code is a portion of
machine code that has not yet been
linked into a complete program. It is
the machine code for one particular
library or module that will make up
the completed product.

Observed failure rate

Object recognition
O

Observability is a measure of how well
internal states of a system can be inferred
from knowledge of its external outputs.
The observability and controllability of
a system are mathematical duals. The
concept of observability was introduced
by Hungarian-American engineer
Rudolf E. Kálmán for linear dynamic
systems.

Object recognition is a computer
vision technique for identifying objects in
images or videos. Object recognition is a
key output of deep learning and machine
learning algorithms. When humans look
at a photograph or watch a video, we
can readily spot people, objects, scenes,
and visual details.

The failure rate determined from a
product or test vehicle subjected to an
accelerating stress that may produce
failures attributable to one or more
failure mechanisms.

Oersted
The oersted (symbol Oe) is the unit of
the auxiliary magnetic field H in the
centimetre–gram–second system of units
(CGS). It is equivalent to 1 dyne per
maxwell.

Ohm
The ohm (symbol: Ω) is the SI derived
unit of electrical resistance, named after
German physicist Georg Simon Ohm.
Although several empirically derived
standard units for expressing electrical
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resistance were developed in connection
with early telegraphy practice, the
British Association for the Advancement
of Science proposed a unit derived from
existing units of mass, length and time
and of a convenient size for practical
work as early as 1861. The definition
of the ohm was revised several times.
Today the definition of the ohm is
expressed from the quantum Hall effect.

I=

V
,
R

where I is the current through the
conductor in units of amperes, V is the
voltage measured across the conductor
in units of volts, and R is the resistance
of the conductor in units of ohms. More
specifically, Ohm’s law states that the R
in this relation is constant, independent
of the current.

Ohmmeter
An ohmmeter is an electrical instrument
that measures electrical resistance,
the opposition to an electric current.
Micro-ohmmeters (microhmmeter or
microohmmeter) make low resistance
measurements. Megohmmeters (also a
trademarked device Megger) measure
large values of resistance. The unit of
measurement for resistance is ohms (Ω).

Ohm’s law
Ohm’s law states that the current
through a conductor between two points
is directly proportional to the voltage
across the two points. Introducing
the constant of proportionality, the
resistance, one arrives at the usual
mathematical equation that describes
this relationship:

O

Oil Shale
Oil shale is an organic-rich finegrained sedimentary rock containing
kerogen (a solid mixture of organic
chemical compounds) from which
liquid hydrocarbons, called shale oil
(not to be confused with tight oil crude
oil occurring naturally in shales), can
be produced. Shale oil is a substitute
for conventional crude oil; however,
extracting shale oil from oil shale is
more costly than the production of
conventional crude oil both financially
and in terms of its environmental impact.

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Deposits of oil shale occur around the
world, including major deposits in the
United States. A 2016 estimate of global
deposits set the total world resources
of oil shale equivalent of 6.05 trillion
barrels (962 billion cubic metres) of oil
in place.

high level view of conduit runs for a
PLC control system.

On-premises wiring
On-premises wiring (customer
premises wiring) is customer-owned
telecommunication transmission or
distribution lines. The transmission lines
may be metallic (copper) or optical fiber,
and may be installed within or between
buildings.
Premises wiring may consist of
horizontal wiring, vertical wiring, and
backbone cabling. It may extend from
the point-of-entry to user work areas.
Any type of communications or data
wiring is considered premises wiring,
including telephone, computer/data,
intercom, closed-circuit television.

One-line Diagram
O

A one-line diagram or single-line
diagram (SLD) is a simplified notation
for representing a three-phasepower
system. The one-line diagram has
its largest application in power flow
studies. Electrical elements such
as circuit breakers, transformers,
capacitors, bus bars, and conductors
are shown by standardized schematic
symbols. Instead of representing
each of three phases with a separate
line or terminal, only one conductor
is represented. It is a form of block
diagram graphically depicting the paths
for power flow between entities of the
system. Elements on the diagram do not
represent the physical size or location
of the electrical equipment, but it is
a common convention to organize the
diagram with the same left-to-right, topto-bottom sequence as the switchgear or
other apparatus represented. A one-line
diagram can also be used to show a

Open-circuit Test
The open-circuit test, or “no-load test”,
is one of the methods used in electrical
engineering to determine the no-load
impedance in the excitation branch of a
transformer. The no load is represented
by the open circuit, which is represented
on the right side of the figure as the
“hole” or incomplete part of the circuit.

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Open circuit Voltage
Open-circuit voltage (abbreviated
as OCV or V OC ) is the difference
of electrical potential between two
terminals of a device when disconnected
from any circuit. There is no external
load connected. No external electric
current flows between the terminals.
Alternatively, the open-circuit voltage
may be thought of as the voltage that
must be applied to a solar cell or a
battery to stop the flow of current. It
is sometimes given the symbol Voc. In
network analysis this voltage is also
known as the Thévenin voltage.

Open-circuit Time
Constant Method
The open-circuit time constant method
is an approximate analysis technique
used in electronic circuit design to
determine the corner frequency of
complex circuits. It also is known as the
zero-value time constant technique. The
method provides a quick evaluation,
and identifies the largest contributions
to time constants as a guide to the circuit
improvements.
The basis of the method is the
approximation that the corner frequency
of the amplifier is determined by the
term in the denominator of its transfer
function that is linear in frequency.
This approximation can be extremely
inaccurate in some cases where a zero
in the numerator is near in frequency.

Open-loop gain
The open-loop gain of an operational
amplifier is the gain obtained when no
feedback is used in the circuit. Open
loop gain is usually exceedingly high;
in fact, an ideal operational amplifier
has infinite open-loop gain. Typically
an op-amp may have an open-loop gain
of around 100,000. Normally, feedback
is applied around the op-amp so that
the gain of the overall circuit is defined
and kept to a figure which is more
usable. However the very high gain of
the op-amp enables considerable levels
of feedback to be applied to achieve
required performance. The open-loop
gain of an operational amplifier falls
very rapidly with increasing frequency.
Along with slew rate, this is one of the
reasons why operational amplifiers have
limited bandwidth.

Operational Amplifier
An operational amplifier (often opamp or opamp) is a DC-coupled highgain electronic voltage amplifier with a
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ended output. In this configuration, an
op-amp produces an output potential
(relative to circuit ground) that is
typically hundreds of thousands of
times larger than the potential difference
between its input terminals. Operational
amplifiers had their origins in analog
computers, where they were used to
perform mathematical operations in
many linear, non-linear, and frequencydependent circuits.

case of a fiberscope. Specially designed
fibers are also used for a variety of other
applications, some of them being fiber
optic sensors and fiber lasers.

Optimal Control
Optimal control theory deals with the
problem of finding a control law for
a given system such that a certain
optimality criterion is achieved.

Optical Fiber
O

An optical fiber or optical fiber is a
flexible, transparent fiber made by
drawing glass (silica) or plastic to a
diameter slightly thicker than that of
a human hair. Optical fibers are used
most often as a means to transmit
light between the two ends of the
fiber and find wide usage in fiber-optic
communications, where they permit
transmission over longer distances and
at higher bandwidths (data rates) than
wire cables. Fibers are used instead
of metal wires because signals travel
along them with less loss; in addition,
fibers are immune to electromagnetic
interference, a problem from which
metal wires suffer excessively. Fibers are
also used for illumination and imaging,
and are often wrapped in bundles so that
they may be used to carry light into, or
images out of confined spaces, as in the

It is an extension of the calculus
of variations, and is a mathematical
optimization method for deriving control
policies. The method is largely due to
the work of Lev Pontryagin and Richard
Bellman in the 1950s, after contributions
to calculus of variations by Edward J.
McShane. Optimal control can be seen
as a control strategy in control theory.

Oscillation
Oscillation is the repetitive variation,
typically in time, of some measure
about a central value (often a point of
equilibrium) or between two or more
different states. The term vibration is
precisely used to describe mechanical
oscillation. Familiar examples of
oscillation include a swinging pendulum
and alternating current.

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Oscilloscope
An oscilloscope, previously called an
oscillograph, and informally known as
a scope or o-scope, CRO (for cathoderay oscilloscope), or DSO (for the more
modern digital storage oscilloscope), is
a type of electronic test instrument that
allows observation of varying signal
voltages, usually as a two-dimensional
plot of one or more signals as a function
of time. Other signals (such as sound or
vibration) can be converted to voltages
and displayed.

electrode which produced luminous
brush discharges, which were applied
to the patient’s body to treat various
medical conditions in electrotherapy.

Oversampling

Oudin Coil
An Oudin coil, also called an Oudin
oscillator or Oudin resonator, is a resonant
transformer circuit that generates very
high voltage, high frequency alternating
current (AC) electricity at low current
levels, used in the obsolete medical field
of electrotherapy around the turn of
the 20th century. It is very similar to
a Tesla coil, with the difference being
that the Oudin coil was connected as
an autotransformer. It was invented
in 1893 by French physician Paul
Marie Oudin as a modification of
physician Jacques Arsene d’Arsonval’s
electrotherapy equipment and used in
quack medicine until perhaps 1930. The
high voltage output terminal of the coil
was connected to an insulated handheld

Oversampling is the process of sampling
a signal with a sampling frequency
significantly higher than the Nyquist
rate. Theoretically, a bandwidth-limited
signal can be perfectly reconstructed if
sampled at the Nyquist rate or above
it. The Nyquist rate is defined as twice
the highest frequency component in
the signal. Oversampling improves
resolution, reduces noise and helps
avoid aliasing and phase distortion by
relaxing anti-aliasing filter performance
requirements.

Overshoot (signal)
In signal processing, control theory,
electronics, and mathematics, overshoot
is the occurrence of a signal or function
exceeding its target. It arises especially
in the step response of bandlimited
systems such as low-pass filters. It is
often followed by ringing, and at times
conflated with the latter.

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Overvoltage

Oxygen-free copper

When the voltage in a circuit or part
of it is raised above its upper design
limit, this is known as overvoltage. The
conditions may be hazardous. Depending
on its duration, the overvoltage event
can be transient—a voltage spike—or
permanent, leading to a power surge.

Oxygen-free copper (OFC) or oxygenfree high thermal conductivity (OFHC)
copper is a group of wrought high
conductivity copper alloys that have
been electrolytically refined to reduce
the level of oxygen to .001% or below.

O

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Pp
p-n-p transistor
A PNP transistor is a bipolar
junction transistor constructed by
sandwiching an N-type semiconductor
between two P-type semiconductors.
A PNP transistor has three terminals – a
Collector (C), Emitter (E) and Base (B).
The PNP transistor behaves like two PN
junctions diodes connected back to back.

Padmount transformer
A padmount or pad-mounted
transformer is a ground mounted
electric power distribution transformer
in a locked steel cabinet mounted on
a concrete pad. Since all energized
connection points are securely enclosed in
a grounded metal housing, a padmount
transformer can be installed in places
that do not have room for a fenced
enclosure. Padmount transformers are
used with underground electric power
distribution lines at service drops, to step
down the primary voltage on the line to
the lower secondary voltage supplied to
utility customers. A single transformer
may serve one large building, or many
homes.

Pantograph (rail)
A pantograph (or “pan”) is an apparatus
mounted on the roof of an electric train,
tram or electric bus to collect power
through contact with an overhead
catenary wire. It is a common type of
current collector. Typically, a single wire
is used, with the return current running
through the track. The term stems
from the resemblance of some styles
to the mechanical pantographs used for
copying handwriting and drawings.

P

Partial Discharge
Partial discharge (PD) is a localized
dielectric breakdown (DB) of a small
portion of a solid or fluid electrical
insulation (EI) system under high voltage
(HV) stress, which does not bridge the
space between two conductors. While
a corona discharge (CD) is usually
revealed by a relatively steady glow

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or brush discharge (BD) in air, partial
discharges within solid insulation
system are not visible.
PD can occur in a gaseous, liquid
or solid insulating medium. It often
starts within gas voids, such as voids
in solid epoxy insulation or bubbles
in transformer oil. Protracted partial
discharge can erode solid insulation
and eventually lead to breakdown of
insulation.

Passivity (engineering)
Passivity is a property of engineering
systems, used in a variety of engineering
disciplines, but most commonly found in
analog electronics and control systems.
A passive component, depending on
field, may be either a component
that consumes but does not produce
energy (thermodynamic passivity) or a
component that is incapable of power
gain (incremental passivity).

P

A component that is not passive
is called an active component. An
electronic circuit consisting entirely of
passive components is called a passive
circuit and has the same properties as a
passive component. Used out-of-context
and without a qualifier, the term passive
is ambiguous. Typically, analog designers
use this term to refer to incrementally
passive components and systems, while
control systems engineers will use this
to refer to thermodynamically passive
ones.

Patch cables
A patch cable or patch cord or patch
lead is an electrical or optical cable used
to connect (“patch in”) one electronic
or optical device to another for signal
routing. Devices of different types (e.g.,
a switch connected to a computer, or a
switch to a router) are connected with
patch cords. Patch cords are usually
produced in many different colors so
as to be easily distinguishable, and
are relatively short, perhaps no longer
than two metres. Types of patch cords
include microphone cables, headphone
extension cables, XLR connector, Tiny
Telephone (TT) connector, RCA connector
and ¼» TRS phone connector cables (as
well as modular Ethernet cables), and
thicker, hose-like cords (snake cable)
used to carry video or amplified signals.
However, patch cords typically refer
only to short cords used with patch
panels.

Peak Demand
Peak demand is a historically high point
in the sales record of a particular product.
In terms of energy use, peak demand
describes a period of simultaneous,
strong consumer demand.

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when a voltage is applied to it, it creates
a temperature difference. At the atomic
scale, an applied temperature gradient
causes charge carriers in the material
to diffuse from the hot side to the cold
side.

Pearl Street Station
Pearl Street Station was the first
commercial central power plant in the
US. It was located at 255-257 Pearl Street
in Manhattan on a site measuring 50
by 100 feet (15 by 30 m), just south
of Fulton Street and fired by coal. It
began with one direct current generator,
and it started generating electricity on
September 4, 1882, serving an initial
load of 400 lamps at 82 customers. By
1884, Pearl Street Station was serving
508 customers with 10,164 lamps.
The station was built by the Edison
Illuminating Company, which was
headed by Thomas Edison. The station
was originally powered by custom-made
Porter-Allen high-speed steam engines
designed to provide 175 horsepower
at 700 rpm, but these proved to be
unreliable with their sensitive governors.
They were removed and replaced with
new engines from Armington & Sims
that proved to be much more suitable
for Edison’s dynamos.

Peltier–Seebeck effect
The thermoelectric effect is the direct
conversion of temperature differences
to electric voltage and vice versa via a
thermocouple. A thermoelectric device
creates voltage when there is a different
temperature on each side. Conversely,

Pentagrid Converter
The pentagrid converter is a type of
radio receiving valve (vacuum tube)
with five grids used as the frequency
mixer stage of a superheterodyne radio
receiver.
The pentagrid was part of a line of
development of valves that were able to
take an incoming RF signal and change
its frequency to a fixed intermediate
frequency, which was then amplified
and detected in the remainder of the
receiver circuitry. The device was
generically referred to as a frequency
changer or just mixer.

Pentavalent element
Element whose atoms have five valence
electrons. Used in doping intrinsic
silicon or germanium to produce
n-type semiconductor material. Most
commonly used pentavalent materials
are arsenic and phosphorus.

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Pentode

P

A pentode is an electronic device
having five active electrodes. The term
most commonly applies to a three-grid
amplifying vacuum tube (thermionic
valve), which was invented by Gilles
Holst and Bernhard D.H. Tellegen
in 1926. The pentode consists of an
evacuated glass envelope containing
five electrodes in this order: a cathode
heated by a filament, a control grid, a
screen grid, a suppressor grid, and a
plate (anode). The pentode (called a
“triple-grid amplifier” in some early
literature) was developed from the
tetrode tube by the addition of a third
grid, the suppressor grid. This served
to prevent secondary emission electrons
emitted by the plate from reaching the
screen grid, which caused instability and
parasitic oscillations in the tetrode. The
pentode is closely related to the beam
tetrode. Pentodes were widely used
in industrial and consumer electronic
equipment such as radios and televisions
until the 1960s, when they were replaced
by transistors. Their main use now is
in high power industrial applications
such as radio transmitters. The obsolete
consumer tubes are still used in a few
legacy and specialty vacuum tube audio
devices.

Permanent Magnet
A permanent magnet is an object made
from a material that is magnetized and
creates its own persistent magnetic field.
An everyday example is a refrigerator
magnet used to hold notes on a
refrigerator door. Materials that can be
magnetized, which are also the ones that
are strongly attracted to a magnet, are
called ferromagnetic (or ferrimagnetic).
These include iron, nickel, cobalt, some
alloys of rare-earth metals, and some
naturally occurring minerals such as
lodestone. Although ferromagnetic (and
ferrimagnetic) materials are the only
ones attracted to a magnet strongly
enough to be commonly considered
magnetic, all other substances respond
weakly to a magnetic field, by one of
several other types of magnetism.

Permanent Magnet
Synchronous Generator
A permanent magnet synchronous
generator is a generator where the
excitation field is provided by a

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permanent magnet instead of a coil.
The term synchronous refers here to the
fact that the rotor and magnetic field
rotate with the same speed, because
the magnetic field is generated through
a shaft mounted permanent magnet
mechanism and current is induced into
the stationary armature
Synchronous generators are
the majority source of commercial
electrical energy. They are commonly
used to convert the mechanical power
output of steam turbines, gas turbines,
reciprocating engines and hydro turbines
into electrical power for the grid. Some
designs of Wind turbines also use this
generator type.

of a material to support the formation
of a magnetic field within itself. Hence,
it is the degree of magnetization that
a material obtains in response to an
applied magnetic field. Magnetic
permeability is typically represented by
the (italicized) Greek letter µ. The term
was coined in September 1885 by Oliver
Heaviside. The reciprocal of magnetic
permeability is magnetic reluctance

Personal Computer
A personal computer (PC) is a
multi-purpose computer whose size,
capabilities, and price make it feasible
for individual use. PCs are intended
to be operated directly by an end user,
rather than by a computer expert or
technician. Computer time-sharing
models that were typically used with
larger, more expensive minicomputer
and mainframe systems, to enable them
be used by many people at the same
time, are not used with PCs.

P

Personal Digital Assistant

Permeability
(electromagnetism)
Permeability is the measure of the ability

A personal digital assistant (PDA), also
known as a handheld PC, is a mobile
device that functions as a personal
information manager. PDAs were largely
discontinued in the early 2010s after the
widespread adoption of highly capable
smartphones, in particular those based
on iOS and Android.
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Perturbation Theory
Perturbation theory comprises
mathematical methods for finding an
approximate solution to a problem,
by starting from the exact solution of
a related, simpler problem. A critical
feature of the technique is a middle step
that breaks the problem into “solvable”
and “perturbation” parts. Perturbation
theory is applicable if the problem at
hand cannot be solved exactly, but can
be formulated by adding a “small” term
to the mathematical description of the
exactly solvable problem.

Petroleum

P

Petroleum is a naturally occurring,
yellow-to-black liquid found in geological
formations beneath the Earth’s surface.
It is commonly refined into various
types of fuels. Components of petroleum
are separated using a technique called
fractional distillation i.e. separation of
a liquid mixture into fractions differing
in boiling point by means of distillation,
typically using a fractionating column.

acidity or alkalinity expressed as pH.
The pH meter measures the difference
in electrical potential between a pH
electrode and a reference electrode, and
so the pH meter is sometimes referred
to as a “potentiometric pH meter”. The
difference in electrical potential relates
to the acidity or pH of the solution. The
pH meter is used in many applications
ranging from laboratory experimentation
to quality control.

Phase converter
A phase converter is a device that
converts electric power provided as
single phase to multiple phase or vice
versa. The majority of phase converters
are used to produce three-phase electric
power from a single-phase source, thus
allowing the operation of three-phase
equipment at a site that only has singlephase electrical service. Phase converters
are used where three-phase service is
not available from the utility, or is too
costly to install due to a remote location.
A utility will generally charge a higher
fee for a three-phase service because of
the extra equipment for transformers
and metering and the extra transmission
wire.

pH meter
A pH meter is a scientific instrument
that measures the hydrogen-ion activity
in water-based solutions, indicating its
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Phase locked loop

Phasor Measurement Unit

A phase-locked loop or phase lock loop
abbreviated as PLL is a control system
that generates an output signal whose
phase is related to the phase of an input
signal. There are several different types;
the simplest is an electronic circuit
consisting of a variable frequency
oscillator and a phase detector in a
feedback loop. The oscillator generates
a periodic signal, and the phase detector
compares the phase of that signal with
the phase of the input periodic signal,
adjusting the oscillator to keep the
phases matched.

A phasor measurement unit (PMU) is
a device which measures the electrical
waves on an electricity grid using a
common time source for synchronization.
Time
synchronization
allows
synchronized real-time measurements
of multiple remote measurement points
on the grid. The resulting measurement
is known as a synchrophasor. PMUs
are considered to be one of the most
important measuring devices in the
future of power systems. A PMU can be
a dedicated device, or the PMU function
can be incorporated into a protective
relay or other device.

Phase Modulation
Phase modulation (PM) is a modulation
pattern for conditioning communication
signals for transmission. It encodes a
message signal as variations in the
instantaneous phase of a carrier wave.
Phase modulation is one of the two
principle forms of angle modulation,
together with frequency modulation.
The phase of a carrier signal is
modulated to follow the changing signal
level (amplitude) of the message signal.
The peak amplitude and the frequency
of the carrier signal are maintained
constant, but as the amplitude of the
message signal changes, the phase of
the carrier changes correspondingly.

Photodiode
A photodiode is a semiconductor device
that converts light into an electrical
current. The current is generated when
photons are absorbed in the photodiode.
Photodiodes may contain optical filters,
built-in lenses, and may have large or
small surface areas. Photodiodes usually
have a slower response time as their
surface area increases. The common,
traditional solar cell used to generate
electric solar power is a large area
photodiode.

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Photonics

P

Photonics is the physical science of
light (photon) generation, detection,
and manipulation through emission,
transmission, modulation, signal
processing, switching, amplification,
and detection/sensing. Though covering
all light’s technical applications over
the whole spectrum, most photonic
applications are in the range of visible
and near-infrared light. The term
photonics developed as an outgrowth
of the first practical semiconductor light
emitters invented in the early 1960s and
optical fibers developed in the 1970s.

PID controller
A proportional–integral–derivative
controller (PID controller or three term
controller) is a control loop feedback
mechanism widely used in industrial
control systems and a variety of other
applications requiring continuously
modulated control. A PID controller
continuously calculates an error value
e(t) as the difference between a desired
setpoint (SP) and a measured process
variable (PV) and applies a correction
based on proportional, integral, and
derivative terms (denoted P, I, and D
respectively) which give the controller
its name

Piezoelectric Effect

Picofarad
A unit of capacitance equal to one
trillionth (10-12) of a farad.

Piezoelectricity is the electric charge that
accumulates in certain solids materials
(such as crystals, certain ceramics, and
biological matter such as bone, DNA
and various proteins) in response to
applied mechanical stress. The word
piezoelectricity means electricity
resulting from pressure and latent heat.

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Piezoelectric Motor
A piezoelectric motor or piezo motor
is a type of electric motor based on
the change in shape of a piezoelectric
material when an electric field is applied.
Piezoelectric motors use the converse
piezoelectric effect of piezoelectric
sensors, in which deformation or
vibration of the piezoelectric material
produces an electric charge. An electrical
circuit makes acoustic or ultrasonic
vibrations in the piezoelectric material,
which produce linear or rotary motion.
In one mechanism, the elongation in a
single plane makes a series of stretches
and position holds, analogous to the
way a caterpillar moves.

over-consumption of the product. Oftencited examples of such externalities are
environmental pollution, and increased
public healthcare costs associated with
tobacco and sugary drink consumption.

PIN Diode
A PIN diode is a diode with a wide,
undoped intrinsic semiconductor region
between a p-type semiconductor and
an n-type semiconductor region. The
p-type and n-type regions are typically
heavily doped because they are used
for ohmic contacts.

Planar Graph

Pigovian Tax
A Pigovian tax (also spelled Pigouvian
tax) is a tax on any market activity that
generates negative externalities (costs
not included in the market price). The
tax is intended to correct an inefficient
market outcome, and does so by being
set equal to the social cost of the negative
externalities. In the presence of negative
externalities, the social cost of a market
activity is not covered by the private cost
of the activity. In such a case, the market
outcome is not efficient and may lead to

A planar graph is a graph that can be
embedded in the plane, i.e., it can be
drawn on the plane in such a way that its
edges intersect only at their endpoints.
In other words, it can be drawn in such
a way that no edges cross each other.
Such a drawing is called a plane graph
or planar embedding of the graph. A
plane graph can be defined as a planar
graph with a mapping from every node
to a point on a plane, and from every
edge to a plane curve on that plane,
such that the extreme points of each
curve are the points mapped from its
end nodes, and all curves are disjoint
except on their extreme points.

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Plasma (physics)
Plasma is one of the four fundamental
states of matter, and was first described
by chemist Irving Langmuir in the
1920s. Unlike the other three states,
solid, liquid, and gas, plasma does
not exist freely on the Earth’s surface
under normal conditions. Plasma can
only be artificially generated by heating
or subjecting a neutral gas to a strong
electromagnetic field to the point an
ionised gaseous substance becomes
increasingly electrically conductive,
and long-range electromagnetic fields
dominate the behavior of the matter.

(positive) side contains an excess of holes,
while the “n” (negative) side contains an
excess of electrons in the outer shells of
the electrically neutral atoms there. This
allows electrical current to pass through
the junction only in one direction. The
p-n junction is created by doping, for
example by ion implantation, diffusion
of dopants, or by epitaxy (growing a
layer of crystal doped with one type of
dopant on top of a layer of crystal doped
with another type of dopant). If two
separate pieces of material were used,
this would introduce a grain boundary
between the semiconductors that would
severely inhibit its utility by scattering
the electrons and holes.

Polyethylene
P

Plug-in hybrid
A plug-in hybrid electric vehicle (PHEV)
is a hybrid electric vehicle that can be
recharged by plugging it in to an external
source of electric power as well by its
on-board engine and generator. Most
PHEVs are passenger cars but there
are also PHEV versions of commercial
vehicles and vans, utility trucks, buses,
trains, motorcycles, scooters, and
military vehicles.

Polyethylene or polythene (abbreviated
PE; IUPAC name polyethene or
poly(ethylene)) is the most common
plastic. The annual global production
is around 80 million tonnes. Its primary
use is in packaging (plastic bags,
plastic films, geomembranes, containers
including bottles, etc.). Many kinds of
polyethylene are known, with most
having the chemical formula (C2H4)n. PE
is usually a mixture of similar polymers
of ethylene with various values of n.

P-N junction

Polymer

A p–n junction is a boundary or interface
between two types of semiconductor
materials, p-type and n-type, inside a
single crystal of semiconductor. The “p”

A polymer is a large molecule, or
macromolecule, composed of many
repeated subunits. Because of their
broad range of properties, both synthetic

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and natural polymers play essential
and ubiquitous roles in everyday life.
Polymers range from familiar synthetic
plastics such as polystyrene to natural
biopolymers such as DNA and proteins
that are fundamental to biological
structure and function. Polymers, both
natural and synthetic, are created
via polymerization of many small
molecules, known as monomers. Their
consequently large molecular mass
relative to small molecule compounds
produces unique physical properties,
including toughness, viscoelasticity,
and a tendency to form glasses and
semicrystalline structures rather than
crystals.

Polyphase system
A polyphase system is a means of
distributing alternating-current electrical
power. Polyphase systems have three or
more energized electrical conductors
carrying alternating currents with
a defined phase angle between the
voltage waves in each conductor; for
three-phase voltage, the phase angle is
120° or ~2.09 radians. Polyphase systems
are particularly useful for transmitting
power to electric motors.

Port (circuit theory)
Polyphase coil
Polyphase coils are electromagnetic
coils connected together in a polyphase
system such as a generator or motor. In
modern systems, the number of phases is
usually three or a multiple of three. Each
phase carries a sinusoidal alternating
current whose phase is delayed relative
to one of its neighbours and advanced
relative to its other neighbour. The phase
currents are separated in time evenly
within each period of the alternating
current. For example, in a three-phase
system, the phases are separated from
each other by one-third of the period.

A port is a pair of terminals connecting
an electrical network or circuit to an
external circuit, a point of entry or exit
for electrical energy. A port consists of
two nodes (terminals) connected to
an outside circuit, that meets the port
condition; the currents flowing into the
two nodes must be equal and opposite.

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Positive Feedback

Power BJT

Positive feedback is a process that occurs
in a feedback loop in which the effects
of a small disturbance on a system
include an increase in the magnitude
of the perturbation. That is, A produces
more of B which in turn produces more
of A. In contrast, a system in which
the results of a change act to reduce
or counteract it has negative feedback.
Both concepts play an important role
in science and engineering, including
biology, chemistry, and cybernetics.

A bipolar junction transistor (bipolar
transistor or BJT) is a type of transistor
that uses both electron and hole charge
carriers. In contrast, unipolar transistors,
such as field-effect transistors, only
use one kind of charge carrier. For
their operation, BJTs use two junctions
between two semiconductor types,
n-type and p-type.

Potentiometer
A potentiometer is a three-terminal
resistor with a sliding or rotating contact
that forms an adjustable voltage divider.
If only two terminals are used, one end
and the wiper, it acts as a variable
resistor or rheostat.
BJTs are manufactured in two types,
NPN and PNP, and are available as
individual components, or fabricated
in integrated circuits, often in large
numbers. The basic function of a BJT
is to amplify current. This allows BJTs to
be used as amplifiers or switches, giving
them wide applicability in electronic
equipment, including computers,
televisions, mobile phones, audio
amplifiers, industrial control, and radio
transmitters.

P

Power
Power is the rate of doing work, the
amount of energy transferred per unit
time. Having no direction, it is a scalar
quantity. In the International System
of Units, the unit of power is the joule
per second (J/s), known as the watt in
honor of James Watt, the eighteenthcentury developer of the steam engine
condenser.

Power cable
A power cable is an electrical cable,
an assembly of one or more electrical
conductors, usually held together
with an overall sheath. The assembly
is used for transmission of electrical
power. Power cables may be installed
as permanent wiring within buildings,

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buried in the ground, run overhead,
or exposed.

Power Conditioner
A power conditioner (also known
as a line conditioner or power line
conditioner) is a device intended to
improve the quality of the power that
is delivered to electrical load equipment.
While there is no official definition of a
power conditioner, the term most often
refers to a device that acts in one or
more ways to deliver a voltage of the
proper level and characteristics to enable
load equipment to function properly.
In some uses, power conditioner refers
to a voltage regulator with at least
one other function to improve power
quality (e.g. power factor correction,
noise suppression, transient impulse
protection, etc.)

Power Converter

Power Distribution
Electric power distribution is the final
stage in the delivery of electric power; it
carries electricity from the transmission
system to individual consumers.
Distribution substations connect to
the transmission system and lower the
transmission voltage to medium voltage
ranging between 2 kV and 35 kV with
the use of transformers.

Power Electronics

Power conversion is converting electric
energy from one form to another such
as converting between AC and DC; or
just changing the voltage or frequency;
or some combination of these. A power
converter is an electrical or electromechanical device for converting
electrical energy. This could be as
simple as a transformer to change the
voltage of AC power, but also includes
far more complex systems. The term
can also refer to a class of electrical
machinery that is used to convert one
frequency of alternating current into
another frequency.

Power electronics is the application of
solid-state electronics to the control
and conversion of electric power. The
first high power electronic devices were
mercury-arc valves. In modern systems
the conversion is performed with
semiconductor switching devices such
as diodes, thyristors and transistors,
pioneered by R. D. Middlebrook and
others beginning in the 1950s. In
contrast to electronic systems concerned
with transmission and processing of
signals and data, in power electronics
substantial amounts of electrical energy
are processed.

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of its theoretical base from electrical
engineering.

Power Generation

Power engineering
Power engineering, also called power
systems engineering, is a subfield of
electrical engineering that deals with the
generation, transmission, distribution
and utilization of electric power, and
the electrical apparatus connected to
such systems.

Electricity generation is the process of
generating electric power from sources
of primary energy. For electric utilities
in the electric power industry, it is the
first stage in the delivery of electricity
to end users, the other stages being
transmission, distribution, energy
storage and recovery, using pumpedstorage methods.

Power Grid
An electrical grid is an interconnected
network for delivering electricity from
producers to consumers. It consists of
generating stations that produce electrical
power, high voltage transmission lines
that carry power from distant sources to
demand centers, and distribution lines
that connect individual customers.

P

Although much of the field is concerned
with the problems of three-phase AC
power – the standard for large-scale
power transmission and distribution
across the modern world a significant
fraction of the field is concerned with the
conversion between AC and DC power
and the development of specialized
power systems such as those used in
aircraft or for electric railway networks.
Power engineering draws the majority
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Power inverter

Power Rating

A power inverter, or inverter, is an
electronic device or circuitry that changes
direct current (DC) to alternating current
(AC).

The power rating of equipment is
the highest power input allowed to
flow through particular equipment.
According to the particular discipline,
the term “power” may refer to the
electrical or mechanical power. A
power rating can also involve average
and maximum power, which may vary
depending on the kind of equipment
and its application.

The input voltage, output voltage
and frequency, and overall power
handling depend on the design of the
specific device or circuitry. The inverter
does not produce any power; the power
is provided by the DC source.

Power rating limits are usually set
as a guideline by the manufacturers,
protecting the equipment and
simplifying the design of larger systems,
by providing a level of operation
under which the equipment will not
be damaged while allowing for a certain
safety margin.

Power Quality
Electric power quality, or simply power
quality, involves voltage, frequency, and
waveform. Good power quality can be
defined as a steady supply voltage that
stays within the prescribed range, steady
a.c. frequency close to the rated value,
and smooth voltage curve waveform
(resembles a sine wave). In general, it is
useful to consider power quality as the
compatibility between what comes out
of an electric outlet and the load that
is plugged into it. The term is used to
describe electric power that drives an
electrical load and the load’s ability to
function properly. Without the proper
power, an electrical device (or load)
may malfunction, fail prematurely or
not operate at all. There are many ways
in which electric power can be of poor
quality and many more causes of such
poor quality power.

P

Power Station
A power station, also referred to as
a power plant or powerhouse and
sometimes generating station or
generating plant, is an industrial facility
for the generation of electric power.
Most power stations contain one or
more generators, a rotating machine
that converts mechanical power into
electrical power.

Precious Metal
A precious metal is a rare, naturally
occurring metallic chemical element of

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high economic value. Chemically, the
precious metals tend to be less reactive
than most elements (see noble metal).
They are usually ductile and have a
high lustre.

Printed circuit boards are used in
all but the simplest electronic products.
They are also used in some electrical
products, such as passive switch boxes.

Process Control
Historically, precious metals were
important as currency but are now
regarded mainly as investment and
industrial commodities. Gold, silver,
platinum, and palladium each have an
ISO 4217 currency code.

Pressure
P

Pressure (symbol: p or P) is the force
applied perpendicular to the surface of
an object per unit area over which that
force is distributed. Gauge pressure (also
spelled gage pressure) is the pressure
relative to the ambient pressure.

Printed Circuit Board
A printed circuit board (PCB)
mechanically supports and electrically
connects electronic components or
electrical components using conductive
tracks, pads and other features etched
from one or more sheet layers of copper
laminated onto and/or between sheet
layers of a non-conductive substrate.
Components are generally soldered onto
the PCB to both electrically connect and
mechanically fasten them to it.

Automatic process control in continuous
production processes is a combination
of control engineering and chemical
engineering disciplines that uses
industrial control systems to achieve a
production level of consistency, economy
and safety which could not be achieved
purely by human manual control. It
is implemented widely in industries
such as oil refining, pulp and paper
manufacturing, chemical processing and
power generating plants.

Product Lifecycle
Management
Product lifecycle management (PLM)
is the process of managing the entire
lifecycle of a product from inception,
through engineering design and
manufacture, to service and disposal of
manufactured products. PLM integrates
people, data, processes and business
systems and provides a product
information backbone for companies
and their extended enterprise.

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Product Safety
Safety standards are standards designed
to ensure the safety of products, activities
or processes, etc. They may be advisory
or compulsory and are normally laid
down by an advisory or regulatory body
that may be either voluntary or statutory.
China has recently experienced trouble
with some of the post listed associations.

Proximity effect
(electromagnetism)
In a conductor carrying alternating
current, if currents are flowing through
one or more other nearby conductors,
such as within a closely wound coil of
wire, the distribution of current within
the first conductor will be constrained
to smaller regions. The resulting current
crowding is termed the proximity effect.
This crowding gives an increase in the
effective resistance of the circuit, which
increases with frequency.

Programmable logic
controller
A programmable logic controller (PLC),
or programmable controller is an
industrial digital computer which has
been ruggedized and adapted for the
control of manufacturing processes, such
as assembly lines, or robotic devices, or
any activity that requires high reliability
control and ease of programming and
process fault diagnosis.

Protoboard
Board with provision for attaching
components without solder. Also
called a breadboard. Primarily used
for constructing experimental circuits.

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Pulse transformer
A pulse transformer is a transformer
that is optimised for transmitting
rectangular electrical pulses (that is,
pulses with fast rise and fall times and
a relatively constant amplitude). Small
versions called signal types are used in
digital logic and telecommunications
circuits, often for matching logic drivers
to transmission lines. Medium-sized
power versions are used in powercontrol circuits such as camera flash
controllers. Larger power versions are
used in the electrical power distribution
industry to interface low-voltage control
circuitry to the high-voltage gates of
power semiconductors. Special high
voltage pulse transformers are also
used to generate high power pulses for
radar, particle accelerators, or other high
energy pulsed power applications.

Pulse-width Modulation
Pulse-width modulation (PWM), or
pulse-duration modulation (PDM), is a
modulation technique used to encode a
message into a pulsing signal. Although
this modulation technique can be used
to encode information for transmission,
its main use is to allow the control
of the power supplied to electrical
devices, especially to inertial loads such
as motors. In addition, PWM is one
of the two principal algorithms used
in photovoltaic solar battery chargers,
the other being maximum power point
tracking.

Pulse-code modulation

Pulse-amplitude
Modulation (PAM)
P

Demodulation is performed by detecting
the amplitude level of the carrier at
every single period. PAM is a technique
that is also used in PCM.

Pulse-amplitude modulation (PAM), is
a form of signal modulation where the
message information is encoded in the
amplitude of a series of signal pulse.

A pulse modulation technique in which
the amplitude of an analogue signal is
converted to a binary value represented
as a series of pulses.

Pulse-duration modulation

It is an analog pulse modulation scheme
in which the amplitudes of a train of
carrier pulses are varied according to
the sample value of the message signal.

A modulation technique for encoding
the amplitude of a signal right into
a pulse width or duration of another
signal, usually a carrier signal, for
transmission.

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Pulse repetition frequency

Pulse train

The pulse repetition frequency is the
number of pulses of a repeating signal in
a specific time unit, normally measured
in pulses per second. The term is used
within a number of technical disciplines,
notably radar.

Pulse repetition period
Time from the beginning of one pulse to
the beginning of the next. Usually
expressed in microseconds (µs).
PRP decreases as PRF increases.
More pulses occur in a second, less time
from one to the next.

Pulse train is a kind of non-sinusoidal
waveform that includes square waves
(duty cycle of 50%) and similarly
periodic but asymmetrical waves (duty
cycles other than 50%). It is a term
common to synthesizer programming,
and is a typical waveform available on
many synthesizers.

Pulse width
The pulse width is a measure of the
elapsed time between the leading and
trailing edges of a single pulse of energy.
The measure is typically used with
electrical signals and is widely used in
the fields of radar and power supplies.
There are two closely related measures.

Pulse shaper
Pulse shaping consists in adjusting
the spectral and temporal shapes of a
laser pulse to enhance the efficiency of
specific laser-induced processes.

Pumped-storage
Hydroelectricity
Pumped-storage hydroelectricity (PSH),
or pumped hydroelectric energy storage

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(PHES), is a type of hydroelectric energy
storage used by electric power systems
for load balancing. The method stores
energy in the form of gravitational
potential energy of water, pumped
from a lower elevation reservoir to a
higher elevation. Low-cost surplus offpeak electric power is typically used to
run the pumps. During periods of high
electrical demand, the stored water is
released through turbines to produce
electric power. Although the losses of
the pumping process makes the plant
a net consumer of energy overall, the
system increases revenue by selling
more electricity during periods of peak
demand, when electricity prices are
highest

P

that uses a transformer to change
the voltage of a DC power supply.
The distinguishing feature of a pushpull converter is that the transformer
primary is supplied with current from
the input line by pairs of transistors
in a symmetrical push-pull circuit. The
transistors are alternately switched
on and off, periodically reversing the
current in the transformer. Therefore,
current is drawn from the line during
both halves of the switching cycle. This
contrasts with buck-boost converters, in
which the input current is supplied by
a single transistor which is switched
on and off, so current is only drawn
from the line during half the switching
cycle. During the other half the output
power is supplied by energy stored in
inductors or capacitors in the power
supply. Push–pull converters have
steadier input current, create less noise
on the input line, and are more efficient
in higher power applications.

Push–pull Converter
A push–pull converter is a type of DCto-DC converter, a switching converter

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Qq
QAM
Quadrature amplitude modulation is the
name of a family of digital modulation
methods and a related family of analog
modulation methods widely used in
modern telecommunications to transmit
information.

QFN
Quad flat no-lead (QFN) is a small size,
lead-less plastic package with a low
profile, moderate thermal dissipation,
and good electrical performance. It is a
surface mount package with metallized
terminal pads located at the bottom
surface of the package.

Quadrature Booster
Quadrature booster (quad booster,
British usage), is a specialised form of
transformer used to control the flow of
real power on three-phase electricity
transmission networks.

Quality
Quality has a pragmatic interpretation
as the non-inferiority or superiority of
something; it’s also defined as being
suitable for its intended purpose
(fitness for purpose) while satisfying
customer expectations. Quality is a
perceptual, conditional, and somewhat
subjective attribute and may be
understood differently by different
people. Consumers may focus on the
specification quality of a product/service,
or how it compares to competitors
in the marketplace. Producers might
measure the conformance quality, or
degree to which the product/service was
produced correctly. Support personnel
may measure quality in the degree that
a product is reliable, maintainable, or
sustainable.

Quality Control
Quality control, or QC for short, is
a process by which entities review
the quality of all factors involved
in production. ISO 9000 defines
quality control as “A part of quality
management focused on fulfilling
quality requirements”

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Quantization
Quality Factor
In physics and engineering the quality
factor or Q factor is a dimensionless
parameter that describes how
underdamped an oscillator or resonator
is, and characterizes a resonator ’s
bandwidth relative to its center
frequency. Higher Q indicates a lower
rate of energy loss relative to the stored
energy of the resonator; the oscillations
die out more slowly. A pendulum
suspended from a high-quality bearing,
oscillating in air, has a high Q, while
a pendulum immersed in oil has a
low one. Resonators with high quality
factors have low damping, so that they
ring or vibrate longer.
Q

Quantization, in mathematics and
digital signal processing, is the process
of mapping input values from a large
set (often a continuous set) to output
values in a (countable) smaller set.
Rounding and truncation are typical
examples of quantization processes.
Quantization is involved to some degree
in nearly all digital signal processing,
as the process of representing a signal
in digital form ordinarily involves
rounding. Quantization also forms the
core of essentially all lossy compression
algorithms.

Quantity
Quantity is a property that can exist as a
multitude or magnitude. Quantities can
be compared in terms of “more”, “less”,
or “equal”, or by assigning a numerical
value in terms of a unit of measurement.
Quantity is among the basic classes of
things along with quality, substance,
change, and relation. Some quantities are
such by their inner nature (as number),
while others are functioning as states
(properties, dimensions, attributes) of
things such as heavy and light, long and
short, broad and narrow, small and great,
or much and little.

Quiescent point
(Q point) A point on the DC load line
of a given amplifier that represents the
quiescent (no signal) value of output
voltage and current for the circuit.

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Rr
R-C network
RC network, is an electric circuit
composed of resistors and capacitors.
It may be driven by a voltage or current
source and these will produce different
responses.

R-S flip-flop
RS flip flops find uses in many
applications in logic or digital electronic
circuitry.

Radar
Radar is an object-detection system that
uses radio waves to determine the range,
angle, or velocity of objects. It can be
used to detect aircraft, ships, spacecraft,
guided missiles, motor vehicles, weather
formations, and terrain. A radar system
consists of a transmitter producing
electromagnetic waves in the radio or
microwaves domain, a transmitting
antenna, a receiving antenna (often the
same antenna is used for transmitting
and receiving) and a receiver and
processor to determine properties of
the object(s). Radio waves (pulsed or
continuous) from the transmitter reflect
off the object and return to the receiver,
giving information about the object’s
location and speed.

Radar beacon
Radar beacon (short: racon) is – according
to article 1.103 of the International
Telecommunication Union’s (ITU) ITU
Radio Regulations (RR) – defined as “A
transmitter-receiver associated with a
fixed navigational mark which, when
triggered by a radar, automatically
returns a distinctive signal which can
appear on the display of the triggering
radar, providing range, bearing and
identification information.” Each station
(transmitter-receiver, transceiver) shall
be classified by the service in which it
operates permanently or temporarily.

Radar Cross Section
Radar cross-section (RCS) is a measure
of how detectable an object is by radar.
A larger RCS indicates that an object is
more easily detected.

Radio
Radio is the technology of using radio
waves to carry information, such as
sound, by systematically modulating
properties of electromagnetic energy
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waves transmitted through space, such
as their amplitude, frequency, phase, or
pulse width. When radio waves strike
an electrical conductor, the oscillating
fields induce an alternating current in
the conductor. The information in the
waves can be extracted and transformed
back into its original form.

which is applied to the antenna. When
excited by this alternating current, the
antenna radiates radio waves.

Railroad

Radio Frequency

R

Radio frequency (RF) is any of the
electromagnetic wave frequencies that lie
in the range extending from around 20
kHz to 300 GHz, roughly the frequencies
used in radio communication. The term
does not have an official definition,
and different sources specify slightly
different upper and lower bounds for
the frequency range. RF usually refers
to electrical rather than mechanical
oscillations. However, mechanical RF
systems do exist (see mechanical filter
and RF MEMS).

Radio Transmitter
Radio transmitter is an electronic device
which produces radio waves with an
antenna. The transmitter itself generates
a radio frequency alternating current,

Rail transport is a means of transferring
of passengers and goods on wheeled
vehicles running on rails, also known
as tracks. It is also commonly referred
to as train transport. In contrast to
road transport, where vehicles run on
a prepared flat surface, rail vehicles
(rolling stock) are directionally guided
by the tracks on which they run. Tracks
usually consist of steel rails, installed
on ties (sleepers) and ballast, on which
the rolling stock, usually fitted with
metal wheels, moves. Other variations
are also possible, such as slab track,
where the rails are fastened to a concrete
foundation resting on a prepared
subsurface.

Railway Electrification
System
A railway electrification system supplies
electric power to railway trains and
trams without an on-board prime
mover or local fuel supply. Electric
railways use electric locomotives to
haul passengers or freight in separate
cars or electric multiple units, passenger
cars with their own motors. Electricity

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is typically generated in large and
relatively efficient generating stations,
transmitted to the railway network and
distributed to the trains. Some electric
railways have their own dedicated
generating stations and transmission
lines but most purchase power from
an electric utility. The railway usually
provides its own distribution lines,
switches and transformers.

trams, rapid transit systems are electric
railways that operate on an exclusive
right-of-way, which cannot be accessed
by pedestrians or other vehicles of any
sort, and which is often grade separated
in tunnels or on elevated railways.

Real-time Operating
System
Rankine Cycle
The Rankine cycle is a model used
to predict the performance of steam
turbine systems. It was also used to
study the performance of reciprocating
steam engines. The Rankine cycle is
an idealized thermodynamic cycle of
a heat engine that converts heat into
mechanical work while undergoing
phase change. The heat is supplied
externally to a closed loop, which
usually uses water as the working
fluid. It is named after William John
Macquorn Rankine, a Scottish polymath
and Glasgow University professor.

Rapid Transit
Rapid transit or mass rapid transit, also
known as heavy rail, metro, subway,
tube, or underground, is a type of
high-capacity public transport generally
found in urban areas. Unlike buses or

A real-time operating system (RTOS)
is an operating system (OS) intended
to serve real-time applications that
process data as it comes in, typically
without buffer delays. Processing time
requirements (including any OS delay)
are measured in tenths of seconds or
shorter increments of time. A real time
system is a time bound system which
has well defined fixed time constraints.
Processing must be done within the
defined constraints or the system will
fail. They either are event driven or time
sharing. Event driven systems switch
between tasks based on their priorities
while time sharing systems switch the
task based on clock interrupts.

Receiver (radio)
A receiver (radio receiver or simply
radio) is an electronic device that
receives radio waves and converts
the information carried by them to a
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usable form. It is used with an antenna.
The antenna intercepts radio waves
(electromagnetic waves) and converts
them to tiny alternating currents which
are applied to the receiver, and the
receiver extracts the desired information.
The receiver uses electronic filters to
separate the desired radio frequency
signal from all the other signals picked
up by the antenna, an electronic
amplifier to increase the power of
the signal for further processing, and
finally recovers the desired information
through demodulation.

(NiMH), lithium-ion (Li-ion), and
lithium-ion polymer (Li-ion polymer).

Reciprocity
(electromagnetism)

Rechargeable Battery

R

A rechargeable battery, storage battery,
secondary cell, or accumulator is a
type of electrical battery which can be
charged, discharged into a load, and
recharged many times, as opposed to
a disposable or primary battery, which
is supplied fully charged and discarded
after use. It is composed of one or
more electrochemical cells. The term
“accumulator” is used as it accumulates
and stores energy through a reversible
electrochemical reaction. Rechargeable
batteries are produced in many different
shapes and sizes, ranging from button
cells to megawatt systems connected
to stabilize an electrical distribution
network. Several different combinations
of electrode materials and electrolytes
are used, including lead–acid, nickel–
cadmium (NiCd), nickel–metal hydride

Reciprocity refers to a variety of related
theorems involving the interchange
of time-harmonic electric current
densities (sources) and the resulting
electromagnetic fields in Maxwell’s
equations for time-invariant linear media
under certain constraints. Reciprocity
is closely related to the concept of
Hermitian operators from linear algebra,
applied to electromagnetism.

Recombination
Process by which a conduction band
electron gives up energy (in the form
of heat or light) and falls into a valence
band hole.

Rectification
Process that converts alternating current
to direct current.

Rectifier
A rectifier is an electrical device that

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converts alternating current (AC),
which periodically reverses direction,
to direct current (DC), which flows
in only one direction. The process
is known as rectification, since it
“straightens” the direction of current.
Physically, rectifiers take a number of
forms, including vacuum tube diodes,
mercury-arc valves, stacks of copper and
selenium oxide plates, semiconductor
diodes, silicon-controlled rectifiers
and other silicon-based semiconductor
switches. Historically, even synchronous
electromechanical switches and motors
have been used. Early radio receivers,
called crystal radios, used a “cat’s
whisker” of fine wire pressing on a
crystal of galena (lead sulfide) to serve
as a point-contact rectifier or “crystal
detector”.

competitors, the RLS exhibits extremely
fast convergence. However, this benefit
comes at the cost of high computational
complexity.

Reed Switch
The reed switch is an electrical switch
operated by an applied magnetic field.
It was invented at Bell Telephone
Laboratories in 1936 by W. B. Ellwood.
It consists of a pair of contacts
on ferromagnetic metal reeds in a
hermetically sealed glass envelope. The
contacts may be normally open, closing
when a magnetic field is present, or
normally closed and opening when a
magnetic field is applied. The switch
may be actuated by a coil, making a reed
relay, or by bringing a magnet near to
the switch. Once the magnet is pulled
away from the switch, the reed switch
will go back to its original position.

Recursive Least Squares

R

Recursive least squares (RLS) is an
adaptive filter algorithm that recursively
finds the coefficients that minimize
a weighted linear least squares cost
function relating to the input signals.
This approach is in contrast to other
algorithms such as the least mean
squares (LMS) that aim to reduce the
mean square error. In the derivation of
the RLS, the input signals are considered
deterministic, while for the LMS and
similar algorithm they are considered
stochastic. Compared to most of its

Regenerative Circuit
A regenerative circuit is one that
employs an amount of positive feedback
(which is also known as regeneration),
sending part of the output back to

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the input without phase inversion,
which reinforces (amplifies) the signal.
One example is the Schmitt trigger
(which is also known as a regenerative
comparator), but the most common
use of the term is in RF amplifiers,
and especially regenerative receivers,
to increase the gain of a single stage,
allowing a signal to be amplified many
times by the same active device.

used where it is necessary to control
a circuit by a separate low-power
signal, or where several circuits must be
controlled by one signal. The first relays
were used in long distance telegraph
circuits as amplifiers: they repeated the
signal coming in from one circuit and retransmitted it on another circuit. Relays
were used extensively in telephone
exchanges and early computers to
perform logical operations.

Relaxation Oscillator

R

In electronics a relaxation oscillator is
a nonlinear electronic oscillator circuit
that produces a nonsinusoidal repetitive
output signal, such as a triangle wave
or square wave. The circuit consists
of a feedback loop containing a
switching device such as a transistor,
comparator, relay, op amp, or a negative
resistance device like a tunnel diode,
that repetitively charges a capacitor
or inductor through a resistance until
it reaches a threshold level, then
discharges it again.

Relay
A relay is an electrically operated switch.
Many relays use an electromagnet to
mechanically operate a switch, but
other operating principles are also used,
such as solid-state relays. Relays are

Reliability engineering
Reliability engineering is a subdiscipline of systems engineering
that emphasizes dependability in the
lifecycle management of a product.
Dependability, or reliability, describes
the ability of a system or component to
function under stated conditions for a
specified period of time. Reliability is
closely related to availability, which is
typically described as the ability of a
component or system to function at a
specified moment or interval of time.

Reluctance Motor
A reluctance motor is a type of electric
motor that induces non-permanent
magnetic poles on the ferromagnetic
rotor. The rotor does not have any

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Remote Sensing

windings. Torque is generated through
the phenomenon of magnetic reluctance.

Remanence
Remanence or remanent magnetization or
residual magnetism is the magnetization
left behind in a ferromagnetic material
(such as iron) after an external magnetic
field is removed. It is also the measure
of that magnetization. Colloquially,
when a magnet is “magnetized” it has
remanence. The remanence of magnetic
materials provides the magnetic
memory in magnetic storage devices,
and is used as a source of information
on the past Earth’s magnetic field in
paleomagnetism.

Remote Racking System
A remote racking system is a system
that allows an operator to operate a
racking system from a remote location.
It offers a safe alternative to manually
racking circuit breakers, which reduces
the requirement for service personnel to
wear a full-body arc flash hazard suit
for protection.

Remote sensing is the acquisition
of information about an object or
phenomenon without making physical
contact with the object and thus in
contrast to on-site observation. Remote
sensing is used in numerous fields,
including geography, land surveying
and most Earth Science disciplines
(for example, hydrology, ecology,
oceanography, glaciology, geology);
it also has military, intelligence,
commercial, economic, planning, and
humanitarian applications.

Repeating Coil
A repeating coil is a voice-frequency
transformer characterized by a closed
magnetic core, a pair of identical
balanced primary (line) windings, a
pair of identical but not necessarily
balanced secondary (drop) windings,
and low transmission loss at voice
frequencies. It permits transfer of voice
currents from one winding to another
by magnetic induction, matches line and
drop impedances, and prevents direct
conduction between the line and the
drop.

Repowering
Repowering is the process of replacing
older power stations with newer ones
that either have a greater nameplate
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capacity or more efficiency which results
in a net increase of power generated.
Repowering can happen in several
different ways. It can be as small as
switching out and replacing a boiler, to
as large as replacing the entire system to
create a more powerful system entirely.
There are many upsides to repowering.
The simple act of refurbishing the old
with the new is in itself beneficial
alongside the cost reduction for keeping
the plant running. With less costs and
a higher energy output, the process is
excessively beneficial.

that is a passive electronic component
used to protect against overcurrent
faults in electronic circuits. The device is
also known as a polyfuse or polyswitch.
They are similar in function to PTC
thermistors in certain situations but
operate on mechanical changes instead of
charge carrier effects in semiconductors.

Repulsion Motor
A repulsion motor is a type of electric
motor for using on alternating current
(AC). It was formerly used as a traction
motor for electric trains (e.g. SR Class
CP and SR Class SL electric multiple
units) but has been superseded by other
types of motors. Repulsion motors are
classified under single phase motors. In
repulsion motors the stator windings
are connected directly to the AC power
supply and the rotor is connected to a
commutator and brush assembly, similar
to that of a direct current (DC) motor.
R

Resistive Circuit
A resistive circuit is a circuit containing
only resistors and ideal current and
voltage sources. Analysis of resistive
circuits is less complicated than analysis
of circuits containing capacitors and
inductors. If the sources are constant
(DC) sources, the result is a DC
circuit. For a random resistor network,
the effective resistance and current
distribution properties of the network
can also be modeled in terms of graph
measures and geometrical properties
of network.

Resistor

Resettable Fuse
A resettable fuse is a polymeric positive
temperature coefficient (PPTC) device

A resistor is a passive two-terminal
electrical component that implements
electrical resistance as a circuit element.
In electronic circuits, resistors are used
to reduce current flow, adjust signal
levels, to divide voltages, bias active
elements, and terminate transmission

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lines, among other uses. High-power
resistors that can dissipate many watts
of electrical power as heat, may be used
as part of motor controls, in power
distribution systems, or as test loads
for generators. Fixed resistors have
resistances that only change slightly
with temperature, time or operating
voltage. Variable resistors can be used
to adjust circuit elements (such as a
volume control or a lamp dimmer), or as
sensing devices for heat, light, humidity,
force, or chemical activity.

provide a fastening mechanism (thread,
bayonet, braces, blind mate) and springs
for a low ohmic electric contact while
sparing the gold surface, thus allowing
very high mating cycles and reducing
the insertion force. Research activity
in the area of radio-frequency (RF)
circuit design has surged in the 2000s in
direct response to the enormous market
demand for inexpensive, high-data-rate
wireless transceivers.

Rheoscope
Resolver (electrical)
A resolver is a type of rotary electrical
transformer used for measuring degrees
of rotation. It is considered an analog
device, and has digital counterparts
such as the digital resolver, rotary (or
pulse) encoder

RF Connector
A coaxial RF connector (radio frequency
connector) is an electrical connector
designed to work at radio frequencies
in the multi-megahertz range. RF
connectors are typically used with coaxial
cables and are designed to maintain the
shielding that the coaxial design offers.
Better models also minimize the change
in transmission line impedance at the
connection. Mechanically, they may

A rheoscope is an instrument for
detecting or measuring the viscosity
of a fluid. In the study of blood flow,
a rheoscope is used to observe and
measure the deformation of blood cells
subject to different levels of fluid shear
stress.

Ripple (electrical)
Ripple (specifically ripple voltage)
in electronics is the residual periodic
variation of the DC voltage within a
power supply which has been derived
from an alternating current (AC)
source. This ripple is due to incomplete
suppression of the alternating waveform
after rectification. Ripple voltage
originates as the output of a rectifier
or from generation and commutation
of DC power.

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Robust control
Robust control is an approach to
controller design that explicitly deals
with uncertainty. Robust control methods
are designed to function properly
provided that uncertain parameters or
disturbances are found within some
(typically compact) set. Robust methods
aim to achieve robust performance and/
or stability in the presence of bounded
modeling errors.

RLC Circuit
An RLC circuit is an electrical circuit
consisting of a resistor (R), an inductor
(L), and a capacitor (C), connected in
series or in parallel. The name of the
circuit is derived from the letters that
are used to denote the constituent
components of this circuit, where the
sequence of the components may vary
from RLC.

Robotics

R

Robotics is an interdisciplinary branch
of engineering and science that includes
mechanical engineering, electrical
engineering, computer science, and
others. Robotics deals with the design,
construction, operation, and use of
robots, as well as computer systems
for their control, sensory feedback, and
information processing.

Rogowski Coil
A Rogowski coil, named after Walter
Rogowski, is an electrical device for
measuring alternating current (AC) or
high-speed current pulses. It consists
of a helical coil of wire with the lead
from one end returning through the
centre of the coil to the other end, so
that both terminals are at the same end
of the coil. The whole assembly is then
wrapped around the straight conductor
whose current is to be measured. There
is no metal (iron) core. The winding
density, the diameter of the coil and the
rigidity of the winding are critical for
preserving immunity to external fields
and low sensitivity to the positioning
of the measured conductor.

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Root locus
Root locus analysis is a graphical
method for examining how the roots
of a system change with variation of a
certain system parameter, commonly a
gain within a feedback system. This is
a technique used as a stability criterion
in the field of classical control theory
developed by Walter R. Evans which can
determine stability of the system. The
root locus plots the poles of the closed
loop transfer function in the complex
s-plane as a function of a gain parameter
(see pole–zero plot).

motion of a shaft or axle to an analog
or digital signal.
There are two main types: absolute
and incremental (relative). The output of
absolute encoders indicates the current
position of the shaft, making them angle
transducers. The output of incremental
encoders provides information about
the motion of the shaft, which is
typically further processed elsewhere
into information such as speed, distance
and position.

Rotary converter
A rotary converter is a type of electrical
machine which acts as a mechanical
rectifier, inverter or frequency converter.
Rotary converters were used to convert
alternating current (AC) to direct current
(DC), or DC to AC power, before the
advent of chemical or solid state power
rectification and inverting. They were
commonly used to provide DC power
for commercial, industrial and railway
electrification from an AC power source.
R

Rotary switch
Rotary encoder
A rotary encoder, also called a shaft
encoder, is an electro-mechanical device
that converts the angular position or

A rotary switch is a switch operated by
rotation. These are often chosen when
more than 2 positions are needed, such
as a three-speed fan or a CB radio with
multiple frequencies of reception or
“channels”.

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Rotor (electric)
The rotor is a moving component of an
electromagnetic system in the electric
motor, electric generator, or alternator.
Its rotation is due to the interaction
between the windings and magnetic
fields which produces a torque around
the rotor’s axis.

Rotary Transformer
A rotary (rotatory) transformer is a
specialized transformer used to couple
electrical signals between two parts that
rotate in relation to each other. They
may be either cylindrical or ‘pancake’
shaped.

R

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Ss

Sample and Hold

S-parameters
S-Parameters are used to describe the
relationship between different ports,
when it becomes especially important to
describe a network in terms of amplitude
and phase versus frequencies, rather
than voltages and currents.

S-plane
The s-plane is the complex plane on
which Laplace transforms are graphed.
It is a mathematical domain where,
instead of viewing processes in the
time domain modeled with time-based
functions, they are viewed as equations
in the frequency domain.

In electronics, a sample and hold (S/H,
also “follow-and-hold”) circuit is an
analog device that samples (captures,
takes) the voltage of a continuously
varying analog signal and holds (locks,
freezes) its value at a constant level for
a specified minimum period of time.
Sample and hold circuits and related
peak detectors are the elementary analog
memory devices. They are typically
used in analog-to-digital converters to
eliminate variations in input signal that
can corrupt the conversion process.

Sampling (Information
Theory)

Sallen–Key filter
The Sallen–Key topology is an electronic
filter topology used to implement
second-order active filters that is
particularly valued for its simplicity.
It is a degenerate form of a voltagecontrolled voltage-source (VCVS) filter
topology.

In signal processing, sampling is the
reduction of a continuous-time signal
to a discrete-time signal. A common
example is the conversion of a sound
wave (a continuous signal) to a sequence
of samples (a discrete-time signal). A
sample is a value or set of values at a
point in time and/or space. A sampler
is a subsystem or operation that extracts
samples from a continuous signal. A
theoretical ideal sampler produces
samples equivalent to the instantaneous
value of the continuous signal at the
desired points.

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Satellite Radio

Saturation (Magnetic)

Satellite radio is defined by the
International Telecommunication
Union (ITU)’S ITU Radio Regulations
(RR) as a broadcasting-satellite service.
The satellite’s signals are broadcast
nationwide, across a much wider
geographical area than terrestrial radio
stations, and the service is primarily
intended for the occupants of motor
vehicles. It is available by subscription,
mostly commercial free, and offers
subscribers more stations and a wider
variety of programming options than
terrestrial radio.

Seen in some magnetic materials,
saturation is the state reached when
an increase in applied external
magnetic field H cannot increase the
magnetization of the material further,
so the total magnetic flux density B
more or less levels off. (It continues
to increase very slowly due to the
vacuum permeability.) Saturation is
a characteristic of ferromagnetic and
ferrimagnetic materials, such as iron,
nickel, cobalt and their alloys.

Satellite

S

In the context of spaceflight, a satellite
is an artificial object which has been
intentionally placed into orbit. Such
objects are sometimes called artificial
satellites to distinguish them from
natural satellites such as Earth’s Moon.
In 1957 the Soviet Union launched the
world’s first artificial satellite, Sputnik
1. Since then, about 6,600 satellites
from more than 40 countries have been
launched.

Schmitt Trigger
In electronics, a Schmitt trigger is a
comparator circuit with hysteresis
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implemented by applying positive
feedback to the noninverting input of
a comparator or differential amplifier.
It is an active circuit which converts an
analog input signal to a digital output
signal. The circuit is named a “trigger”
because the output retains its value
until the input changes sufficiently to
trigger a change. In the non-inverting
configuration, when the input is higher
than a chosen threshold, the output is
high. When the input is below a different
(lower) chosen threshold the output is
low, and when the input is between the
two levels the output retains its value.

Schottky Diode

Scott-T transformer
A Scott-T transformer (also called a
Scott connection) is a type of circuit
used to derive two-phase electric power
(2-φ, 90-degree phase rotation) from
a three-phase (3-φ, 120-degree phase
rotation) source, or vice versa. The Scott
connection evenly distributes a balanced
load between the phases of the source.
The Scott three-phase transformer was
invented by a Westinghouse engineer
Charles F. Scott in the late 1890s to
bypass Thomas Edison’s more expensive
rotary converter and thereby permit
two-phase generator plants to drive
three-phase motors.

The Schottky diode (named after the
German physicist Walter H. Schottky),
also known as Schottky barrier diode
or hot-carrier diode, is a semiconductor
diode formed by the junction of a
semiconductor with a metal. It has
a low forward voltage drop and a
very fast switching action. The cat’swhisker detectors used in the early
days of wireless and metal rectifiers
used in early power applications can be
considered primitive Schottky diodes.

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Selenium Rectifiers
A selenium rectifier is a type of metal
rectifier, invented in 1933. They were
used in power supplies for electronic
equipment, and in high current battery
charger applications until they were
superseded by silicon diode rectifiers
in the late 1960s. The arrival of the
alternator in some automobiles was the
result of compact, low cost, high current
silicon rectifiers. These units were small
enough to be inside the alternator
case, unlike the selenium units that
preceded silicon devices. The rectifying
properties of selenium, amongst other
semiconductors, were observed by
Braun, Schuster and Siemens between
1874 to 1883.

Semiconductor device
Semiconductor devices are electronic
components that exploit the electronic
properties of semiconductor materials,
principally silicon, germanium, and
gallium arsenide, as well as organic
semiconductors. Semiconductor devices
have replaced thermionic devices
(vacuum tubes) in most applications.
They use electronic conduction in the
solid state as opposed to the gaseous
state or thermionic emission in a high
vacuum. Semiconductor devices are
manufactured both as single discrete
devices and as integrated circuits (ICs),
which consist of a number—from a few
(as low as two) to billions—of devices
manufactured and interconnected on
a single semiconductor substrate, or
wafer.

Selenium
S

Selenium is a chemical element with
symbol Se and atomic number 34. It
is a nonmetal with properties that are
intermediate between the elements above
and below in the periodic table, sulfur
and tellurium, and also has similarities to
arsenic. It rarely occurs in its elemental
state or as pure ore compounds in the
Earth’s crust. Selenium was discovered
in 1817 by Jöns Jacob Berzelius, who
noted the similarity of the new element
to the previously discovered tellurium
(named for the Earth).

Semiconductor fabrication
Semiconductor device fabrication
is the process used to create the
integrated circuits that are present
in everyday electrical and electronic

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devices. It is a multiple-step sequence
of photolithographic and chemical
processing steps during which electronic
circuits are gradually created on a wafer
made of pure semiconducting material.
Silicon is almost always used, but
various compound semiconductors are
used for specialized applications. The
entire manufacturing process, from start
to packaged chips ready for shipment,
takes six to eight weeks and is performed
in highly specialized facilities referred
to as fabs.

Sensor
In the broadest definition, a sensor
is a device, module, or subsystem
whose purpose is to detect events or
changes in its environment and send
the information to other electronics,
frequently a computer processor.
A sensor is always used with other
electronics, whether as simple as a light
or as complex as a computer.

Semiconductor
A semiconductor material has an
electrical conductivity value falling
between that of a conductor – such as
copper, gold etc. – and an insulator,
such as glass. Their resistance decreases
as their temperature increases, which
is behavior opposite to that of a metal.
Their conducting properties may be
altered in useful ways by the deliberate,
controlled introduction of impurities
(“doping”) into the crystal structure.

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Serial communication
In telecommunication and data
transmission, serial communication is
the process of sending data one bit at a
time, sequentially, over a communication
channel or computer bus. This is in
contrast to parallel communication,
where several bits are sent as a whole,
on a link with several parallel channels.

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efforts have been going on since the
1980s.

Series and Parallel
Circuits

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Shaded-pole Motor

Components of an electrical circuit or
electronic circuit can be connected in
many different ways. The two simplest
of these are called series and parallel
and occur frequently. Components
connected in series are connected along
a single path, so the same current
flows through all of the components.
Components connected in parallel are
connected along multiple paths, so
the same voltage is applied to each
component.

The shaded-pole motor is the original
type of AC single-phase induction motor.
A shaded-pole motor is a small squirrelcage motor in which the auxiliary
winding is composed of a copper ring
or bar surrounding a portion of each
pole. This auxiliary single-turn winding
is called a shading coil.

SETI

Shaft Voltage

The search for extraterrestrial intelligence
(SETI) is a collective term for scientific
searches for intelligent extraterrestrial
life, for example, monitoring
electromagnetic radiation for signs of
transmissions from civilizations on other
planets. Scientific investigation began
shortly after the advent of radio in the
early 1900s, and focused international

Shaft voltage occurs in electric motors
and generators due to leakage, induction,
or capacitive coupling with the windings
of the motor. It can occur in motors
powered by variable-frequency drives,
as often used in heating, ventilation, air
conditioning and refrigeration systems.
DC machines may have leakage current
from the armature windings that
energizes the shaft.

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Shunt (Electrical)

Short Circuit
A short circuit (sometimes abbreviated
to short or s/c) is an electrical circuit
that allows a current to travel along
an unintended path with no or a very
low electrical impedance. The electrical
opposite of a short circuit is an “open
circuit”, which is an infinite resistance
between two nodes. It is common to
misuse “short circuit” to describe any
electrical malfunction, regardless of the
actual problem.

In electronics, a shunt is a device which
allows electric current to pass around
another point in the circuit by creating
a low resistance path. The term is also
widely used in photovoltaics to describe
an unwanted short circuit between the
front and back surface contacts of a solar
cell, usually caused by wafer damage.
The origin of the term is in the verb ‘to
shunt’ meaning to turn away or follow
a different path.

SI

Short-circuit Test
The purpose of a short-circuit test is to
determine the series branch parameters
of the equivalent circuit of a real
transformer.

The International System of Units
(SI, abbreviated from the French
Système international (d’unités)) is the
modern form of the metric system,
and is the most widely used system of
measurement. It comprises a coherent
system of units of measurement built
on seven base units (ampere, kelvin,
second, metre, kilogram, candela, mole)
and a set of twenty decimal prefixes to
the unit names and unit symbols that

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may be used when specifying multiples
and fractions of the units. The system
also specifies names for 22 derived units
for other common physical quantities
like lumen, watt, etc.

Signal (Electrical
Engineering)
A signal as referred to in communication
systems, signal processing, and electrical
engineering is a function that “conveys
information about the behavior or
attributes of some phenomenon”. In the
physical world, any quantity exhibiting
variation in time or variation in space
(such as an image) is potentially a
signal that might provide information
on the status of a physical system, or
convey a message between observers,
among other possibilities. The IEEE
Transactions on Signal Processing states
that the term “signal” includes audio,
video, speech, image, communication,
geophysical, sonar, radar, medical and
musical signals.

Siemens (Unit)

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The siemens (symbol: S) is the derived
unit of electric conductance, electric
susceptance and electric admittance
in the International System of Units
(SI). Conductance, susceptance, and
admittance are the reciprocals of
resistance, reactance, and impedance
respectively; hence one siemens is
redundantly equal to the reciprocal of
one ohm, and is also referred to as the
mho. The 14th General Conference on
Weights and Measures approved the
addition of the siemens as a derived
unit in 1971.

Signal Processing
Signal processing concerns the
analysis, synthesis, and modification
of signals, which are broadly defined
as functions conveying, “information
about the behavior or attributes of some
phenomenon”, such as sound, images,
and biological measurements. For
example, signal processing techniques
are used to improve signal transmission
fidelity, storage efficiency, and subjective
quality, and to emphasize or detect
components of interest in a measured
signal.

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Signal Strength
In telecommunications, particularly in
radio frequency, signal strength (also
referred to as field strength) refers to
the transmitter power output as received
by a reference antenna at a distance
from the transmitting antenna. Highpowered transmissions, such as those
used in broadcasting, are expressed
in dB-millivolts per metre (dBmV/m).
For very low-power systems, such
as mobile phones, signal strength is
usually expressed in dB-microvolts per
metre (dBµV/m) or in decibels above a
reference level of one milliwatt (dBm).
In broadcasting terminology, 1 mV/m
is 1000 µV/m or 60 dBµ (often written
dBu).

the term, is a specialized flow graph, a
directed graph in which nodes represent
system variables, and branches (edges,
arcs, or arrows) represent functional
connections between pairs of nodes.
Thus, signal-flow graph theory builds
on that of directed graphs (also called
digraphs), which includes as well that
of oriented graphs. This mathematical
theory of digraphs exists, of course,
quite apart from its applications.

Signal-to-noise Ratio
Signal-to-noise ratio is a measure used in
science and engineering that compares
the level of a desired signal to the level
of background noise.

Silicon controlled rectifier

Signal-flow Graph
A signal-flow graph or signal-flowgraph
(SFG), invented by Claude Shannon,
but often called a Mason graph after
Samuel Jefferson Mason who coined

A silicon controlled rectifier or
semiconductor-controlled rectifier is a
four-layer solid-state current-controlling
device. The principle of four layer p-np-n switching was developed by Moll,
Tanenbaum, Goldey and Holonyak of
Bell Laboratories in 1956. The practical
demonstration of silicon controlled
switching and detailed theoretical
behavior of a device in agreement
with the experimental results was
presented by Dr Ian M. Mackintosh of
Bell Laboratories in January 1958.

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chemical affinity for oxygen; as such, it
was first prepared and characterized in
pure form only in 1823 by Jöns Jakob
Berzelius.

Silicon Valley
Silicon Valley is a nickname for the
southern portion of the San Francisco
Bay Area in the northern part of the U.S.
state of California. The “valley” in its
name refers to the Santa Clara Valley in
Santa Clara County, which includes the
city of San Jose and surrounding cities
and towns, where the region has been
traditionally centered. The region has
expanded to include the southern end
of Santa Clara County down to Gilroy
and southern portions of the East Bay
in Alameda County.

S

Silver
Silver is a chemical element with symbol
Ag and atomic number 47. A soft, white,
lustrous transition metal, it exhibits the
highest electrical conductivity, thermal
conductivity, and reflectivity of any
metal. The metal is found in the Earth’s
crust in the pure, free elemental form
(“native silver”), as an alloy with gold
and other metals, and in minerals such
as argentite and chlorargyrite. Most
silver is produced as a byproduct of
copper, gold, lead, and zinc refining.

Silicon
Silicon is a chemical element with
symbol Si and atomic number 14. A hard
and brittle crystalline solid with a bluegrey metallic lustre, it is a tetravalent
metalloid and semiconductor. It is a
member of group 14 in the periodic
table, along with carbon above it and
germanium, tin, and lead below. It
is rather unreactive, though less so
than germanium, and has a very large

Sine Wave
A sine wave or sinusoid is a mathematical
curve that describes a smooth repetitive
oscillation. A sine wave is a continuous
wave. It is named after the function
sine, of which it is the graph. It occurs
often in pure and applied mathematics,
as well as physics, engineering, signal
processing and many other fields.

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Single-sideband
Modulation

Single-phase Electric
Power
In electrical engineering, single-phase
electric power is the distribution of
alternating current electric power using
a system in which all the voltages of
the supply vary in unison. Single-phase
distribution is used when loads are
mostly lighting and heating, with few
large electric motors. A single-phase
supply connected to an alternating
current electric motor does not produce
a revolving magnetic field; single-phase
motors need additional circuits for
starting (capacitor start motor), and
such motors are uncommon above 10
kW in rating.

In radio communications, singlesideband modulation (SSB) or singlesideband suppressed-carrier modulation
(SSB-SC) is a type of modulation, used
to transmit information, an audio
signal, by radio waves. A refinement
of amplitude modulation, it uses
transmitter power and bandwidth
more efficiently. Amplitude modulation
produces an output signal that has twice
the bandwidth of the original baseband
signal. Single-sideband modulation
avoids this bandwidth doubling, and
the power wasted on a carrier, at the
cost of increased device complexity and
more difficult tuning at the receiver.

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Skin Effect
Skin effect is the tendency of an
alternating electric current (AC) to
become distributed within a conductor
such that the current density is largest
near the surface of the conductor, and

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decreases with greater depths in the
conductor. The electric current flows
mainly at the “skin” of the conductor,
between the outer surface and a
level called the skin depth. The skin
effect causes the effective resistance
of the conductor to increase at higher
frequencies where the skin depth is
smaller, thus reducing the effective
cross-section of the conductor.

Slip Ring
A slip ring is an electromechanical device
that allows the transmission of power
and electrical signals from a stationary
to a rotating structure. A slip ring
can be used in any electromechanical
system that requires rotation while
transmitting power or signals. It can
improve mechanical performance,
simplify system operation and eliminate
damage-prone wires dangling from
movable joints.

Sliding Mode Control

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In control systems, sliding mode
control, or SMC, is a nonlinear control
method that alters the dynamics of a
nonlinear system by application of a
discontinuous control signal (or more
rigorously, a set-valued control signal)
that forces the system to “slide” along
a cross-section of the system’s normal
behavior. The state-feedback control
law is not a continuous function of
time. Instead, it can switch from one
continuous structure to another based
on the current position in the state space.

Small Signal Model
Small-signal modeling is a common
analysis technique in electronics
engineering which is used to
approximate the behavior of electronic
circuits containing nonlinear devices
with linear equations. It is applicable
to electronic circuits in which the AC
signals, the time-varying currents and
voltages in the circuit, have a small
magnitude compared to the DC bias
currents and voltages.

Smart Grid
A smart grid is an electrical grid which
includes a variety of operational and
energy measures including smart
meters, smart appliances, renewable
energy resources, and energy efficient
resources. Electronic power conditioning
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and control of the production and
distribution of electricity are important
aspects of the smart grid.

information processed by computer
systems, programs and data. Computer
software includes computer programs,
libraries and related non-executable
data, such as online documentation or
digital media.

Smith Chart
The Smith chart, invented by Phillip H.
Smith (1905–1987), is a graphical aid
or nomogram designed for electrical
and electronics engineers specializing
in radio frequency (RF) engineering
to assist in solving problems with
transmission lines and matching circuits.

Solar Cell
A solar cell, or photovoltaic cell, is
an electrical device that converts the
energy of light directly into electricity
by the photovoltaic effect, which is a
physical and chemical phenomenon. It
is a form of photoelectric cell, defined as
a device whose electrical characteristics,
such as current, voltage, or resistance,
vary when exposed to light. Individual
solar cell devices can be combined to
form modules, otherwise known as solar
panels.

Software
Computer software, or simply software,
is a part of a computer system
that consists of data or computer
instructions, in contrast to the physical
hardware from which the system is
built. In computer science and software
engineering, computer software is all
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Solar Energy
Solar energy is radiant light and heat
from the Sun that is harnessed using
a range of ever-evolving technologies
such as solar heating, photovoltaics,
solar thermal energy, solar architecture,
molten salt power plants and artificial
photosynthesis.

either directly using photovoltaics (PV),
indirectly using concentrated solar
power, or a combination. Concentrated
solar power systems use lenses or
mirrors and tracking systems to focus a
large area of sunlight into a small beam.
Photovoltaic cells convert light into an
electric current using the photovoltaic
effect.

Solar Micro-inverter
A solar micro-inverter, or simply
microinverter, is a device used in
photovoltaics that converts direct
current (DC) generated by a single solar
module to alternating current (AC).
The output from several microinverters
is combined and often fed to the
electrical grid. Microinverters contrast
with conventional string and central
solar inverters, which are connected to
multiple solar modules or panels of the
PV system.
S

Soldering
Soldering is a process in which two or
more items (usually metal) are joined
together by melting and putting a filler
metal (solder) into the joint, the filler
metal having a lower melting point than
the adjoining metal. Soldering differs
from welding in that soldering does
not involve melting the work pieces.
In brazing, the filler metal melts at a
higher temperature, but the work piece
metal does not melt.

Solar Power
Solar power is the conversion of
energy from sunlight into electricity,
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Solenoid

Solid State Physics

A solenoid is a coil wound into a tightly
packed helix. The term was invented by
French physicist André-Marie Ampère
to designate a helical coil. In physics,
the term refers to a coil whose length is
substantially greater than its diameter,
often wrapped around a metallic core,
which produces a uniform magnetic
field in a volume of space (where some
experiment might be carried out) when
an electric current is passed through it.

Solid-state physics is the study of rigid
matter, or solids, through methods such
as quantum mechanics, crystallography,
electromagnetism, and metallurgy. It is
the largest branch of condensed matter
physics. Solid-state physics studies
how the large-scale properties of solid
materials result from their atomic-scale
properties. Thus, solid-state physics
forms a theoretical basis of materials
science. It also has direct applications,
for example in the technology of
transistors and semiconductors.

Space Flight
Solid State (Electronics)
Solid-state
electronics
means
semiconductor electronics; electronic
equipment using semiconductor
devices such as semiconductor diodes,
transistors, and integrated circuits (ICs).
The term is also used for devices in
which semiconductor electronics which
have no moving parts replace devices
with moving parts, such as the solidstate relay in which transistor switches
are used in place of a moving-arm
electromechanical relay, or the solid
state disk (SSD) a type of semiconductor
memory used in computers to replace
hard disk drives, which store data on
a rotating disk.

Spaceflight (also written space flight)
is ballistic flight into or through outer
space. Spaceflight can occur with
spacecraft with or without humans on
board. Examples of human spaceflight
include the U.S. Apollo Moon landing
and Space Shuttle programs and the
Russian Soyuz program, as well as the
ongoing International Space Station.
Examples of unmanned spaceflight
include space probes that leave Earth
orbit, as well as satellites in orbit around
Earth, such as communications satellites.
These operate either by telerobotic
control or are fully autonomous.

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Space Vector Modulation

Spark-gap Transmitter

Space vector modulation (SVM) is
an algorithm for the control of pulse
width modulation (PWM). It is used
for the creation of alternating current
(AC) waveforms; most commonly to
drive 3 phase AC powered motors at
varying speeds from DC using multiple
class-D amplifiers. There are variations
of SVM that result in different quality
and computational requirements. One
active area of development is in the
reduction of total harmonic distortion
(THD) created by the rapid switching
inherent to these algorithms.

A spark-gap transmitter is a device
that generates radio frequency
electromagnetic waves using a spark
gap. Spark gap transmitters were the first
devices to demonstrate practical radio
transmission, and were the standard
technology for the first three decades of
radio (1887–1916). Later, more efficient
transmitters were developed based on
rotary machines like the high-speed
Alexanderson alternators and the static
Poulsen Arc generators.

Spectrum Analyzer

Spark Spread

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The spark spread is the theoretical
gross margin of a gas-fired power plant
from selling a unit of electricity, having
bought the fuel required to produce
this unit of electricity. All other costs
(operation and maintenance, capital and
other financial costs) must be covered
from the spark spread. The term was
first coined by Tony West’s trading team
on the trading floor of National Power
Ltd in Swindon, UK during the late
1990s and quickly came into common
usage as other traders realised the
trading and hedging opportunities.

A spectrum analyzer measures the
magnitude of an input signal versus
frequency within the full frequency
range of the instrument. The primary use
is to measure the power of the spectrum
of known and unknown signals. The
input signal that a spectrum analyzer
measures is electrical; however, spectral
compositions of other signals, such as
acoustic pressure waves and optical
light waves, can be considered through
the use of an appropriate transducer.
Optical spectrum analyzers also exist,
which use direct optical techniques
such as a monochromator to make
measurements.

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Speech Processing
Speech processing is the study of speech
signals and the processing methods of
these signals. The signals are usually
processed in a digital representation,
so speech processing can be regarded
as a special case of digital signal
processing, applied to speech signal.
Aspects of speech processing includes
the acquisition, manipulation, storage,
transfer and output of speech signals.
The input is called speech recognition
and the output is called speech synthesis.

Square Wave
A square wave is a non-sinusoidal
periodic waveform in which the
amplitude alternates at a steady
frequency between fixed minimum and
maximum values, with the same duration
at minimum and maximum. Although
not realizable in physical systems,
the transition between minimum and
maximum is instantaneous for an ideal
square wave.

SPICE
SPICE (Simulation Program with
Integrated Circuit Emphasis) is a generalpurpose, open source analog electronic
circuit simulator. It is a program used in
integrated circuit and board-level design
to check the integrity of circuit designs
and to predict circuit behavior.

Stability Theory

Split Phase
A split-phase or single-phase threewire system is a type of single-phase
electric power distribution. It is the AC
equivalent of the original Edison threewire direct-current system. Its primary
advantage is that it saves conductor
material over a single-ended singlephase system, while only requiring a
single phase on the supply side of the
distribution transformer.

In mathematics, stability theory
addresses the stability of solutions of
differential equations and of trajectories
of dynamical systems under small
perturbations of initial conditions. The
heat equation, for example, is a stable
partial differential equation because
small perturbations of initial data lead
to small variations in temperature at a
later time as a result of the maximum
principle. In partial differential equations
one may measure the distances between

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functions using Lp norms or the sup
norm, while in differential geometry
one may measure the distance between
spaces using the Gromov–Hausdorff
distance.

Knowing the system state is necessary
to solve many control theory problems;
for example, stabilizing a system using
state feedback.

Stacking Factor
The stacking factor is used in electrical
transformer design. Since transformers
are made up of metal sheets, almost
always iron, they are laminated so
they do not contact each other. This is
done to reduce the intensity of eddy
current losses in the core, while keeping
a high flux carrying capacity. Between
the metal sheets is a non-ferro-magnetic
material, therefore, when calculating the
flux density of the iron core this nonferromagnetic material must be taken
into account. The stacking factor gives
an approximate number to how much
of the core is effective when calculating
flux.

Star-mesh Transform

S

State Space Representation
In control engineering, a state-space
representation is a mathematical model
of a physical system as a set of input,
output and state variables related by
first-order differential equations or
difference equations. State variables are
variables whose values evolve through
time in a way that depends on the values
they have at any given time and also
depends on the externally imposed
values of input variables. Output
variables’ values depend on the values
of the state variables.

The star-mesh transform (or starpolygon transform) is a mathematical
circuit analysis technique to transform
a resistive network into an equivalent
network with one less node. The
equivalence follows from the Schur
complement identity applied to the
Kirchhoff matrix of the network.

Static VAR compensator

State Observer
In control theory, a state observer is a
system that provides an estimate of the
internal state of a given real system,
from measurements of the input and
output of the real system. It is typically
computer-implemented, and provides
the basis of many practical applications.

A static VAR compensator is a set of
electrical devices for providing fastacting reactive power on high-voltage
electricity transmission networks. SVCs
are part of the Flexible AC transmission
system device family, regulating voltage,
power factor, harmonics and stabilizing
the system. A static VAR compensator

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has no significant moving parts (other
than internal switchgear). Prior to the
invention of the SVC, power factor
compensation was the preserve of large
rotating machines such as synchronous
condensers or switched capacitor banks.

Stator
The stator is the stationary part of
a rotary system, found in electric
generators, electric motors, sirens, mud
motors or biological rotors. Energy
flows through a stator to or from the
rotating component of the system. In
an electric motor, the stator provides a
rotating magnetic field that drives the
rotating armature; in a generator, the
stator converts the rotating magnetic
field to electric current. In fluid powered
devices, the stator guides the flow of
fluid to or from the rotating part of
the system.

Steam Turbine
A steam turbine is a device that extracts
thermal energy from pressurized steam
and uses it to do mechanical work on
a rotating output shaft. Its modern
manifestation was invented by Sir
Charles Parsons in 1884. Because the
turbine generates rotary motion, it is
particularly suited to be used to drive
an electrical generator – about 90% of
all electricity generation in the United
States in the year 1996 was by use of
steam turbines. The steam turbine is a
form of heat engine that derives much
of its improvement in thermodynamic
efficiency from the use of multiple
stages in the expansion of the steam,
which results in a closer approach to
the ideal reversible expansion process.

Steel
Steel is an alloy of iron and carbon
and other elements. Because of its high
tensile strength and low cost, it is a
major component used in buildings,
infrastructure, tools, ships, automobiles,
machines, appliances, and weapons.
Iron is the base metal of steel. Iron is
able to take on two crystalline forms
(allotropic forms), body centered cubic
(BCC) and face centered cubic (FCC),
depending on its temperature. In the
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body-centred cubic arrangement, there
is an iron atom in the centre of each
cube, and in the face-centred cubic, there
is one at the center of each of the six
faces of the cube. It is the interaction of
the allotropes of iron with the alloying
elements, primarily carbon that gives
steel and cast iron their range of unique
properties.

Stereophonic Sound

Step Response
The step response of a system in a given
initial state consists of the time evolution
of its outputs when its control inputs are
Heaviside step functions. In electronic
engineering and control theory, step
response is the time behaviour of the
outputs of a general system when its
inputs change from zero to one in a
very short time. The concept can be
extended to the abstract mathematical
notion of a dynamical system using an
evolution parameter.
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Stepper Motor
A stepper motor or step motor or stepping
motor is a brushless DC electric motor
that divides a full rotation into a number
of equal steps. The motor’s position
can then be commanded to move and
hold at one of these steps without any
position sensor for feedback (an openloop controller), as long as the motor
is carefully sized to the application in
respect to torque and speed.

Stereophonic sound or, more
commonly, stereo, is a method of sound
reproduction that creates an illusion of
multi-directional audible perspective.
This is usually achieved by using two
or more independent audio channels
through a configuration of two or more
loudspeakers (or stereo headphones) in
such a way as to create the impression
of sound heard from various directions,
as in natural hearing.

Storage Tube
Storage tubes are a class of cathode-ray
tubes (CRTs) that are designed to hold
an image for a long period of time,
typically as long as power is supplied
to the tube. A specialized type of storage
tube, the Williams tube, was used as a
main memory system on a number of
early computers, from the late 1940s
into the early 1950s. They were replaced
with other technologies, notably core
memory, starting in the 1950s.

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electrical equipment boxes, railway
signal equipment, and third rails or to
supports for overhead lines from the
track. The width of a narrow cut can
also affect the maximum loading gauge.

Stray Capacitance
Any two adjacent conductors can
function as a capacitor, though
the capacitance is small unless the
conductors are close together for long
distances or over a large area. This
(often unwanted) capacitance is called
parasitic or “stray capacitance”. Stray
capacitance can allow signals to leak
between otherwise isolated circuits (an
effect called crosstalk), and it can be a
limiting factor for proper functioning
of circuits at high frequency.

Structured Cabling
In telecommunications, structured
cabling is building or campus cabling
infrastructure that consists of a number
of standardized smaller elements (hence
structured) called subsystems.

Structure Gauge
The structure gauge, also called the
minimum clearance outline, is the
minimum height and width of tunnels
and bridges as well as the minimum
height and width of the doors that allow
a rail siding access into a warehouse.
In addition, the term may apply to the
minimum distance to railway platforms
(passenger or freight), buildings,

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Submarine
Communications Cable
A submarine
communications
cable is a cable laid on the sea bed
between land-based stations to carry
telecommunication signals across
stretches of ocean and sea. The first
submarine communications cables,
laid in the 1850s, carried telegraphy
traffic. Subsequent generations of cables
carried telephone traffic, then data
communications traffic. Modern cables
use optical fiber technology to carry
digital data, which includes telephone,
Internet and private data traffic.

Sulfur Hexafluoride
Sulfur hexafluoride (SF6) is an inorganic,
colorless, odorless, non-flammable,
extremely potent greenhouse gas, and
an excellent electrical insulator. SF6 has
an octahedral geometry, consisting of
six fluorine atoms attached to a central
sulfur atom. It is a hypervalent molecule.
Typical for a nonpolar gas, it is poorly
soluble in water but quite soluble in
nonpolar organic solvents. It is generally
transported as a liquefied compressed
gas. It has a density of 6.12 g/L at sea
level conditions, considerably higher
than the density of air (1.225 g/L).

Sulfur Hexafluoride
Circuit Breaker
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grids at transmission voltages up to 800
kV, as generator circuit breakers, and
in distribution systems at voltages up
to 35 kV.

Sulfur hexafluoride circuit breakers
protect electrical power stations and
distribution systems by interrupting
electric currents, when tripped by a
protective relay. Instead of oil, air, or
a vacuum, a sulfur hexafluoride circuit
breaker uses sulfur hexafluoride (SF6)
gas to cool and quench the arc on
opening a circuit. Advantages over
other media include lower operating
noise and no emission of hot gases, and
relatively low maintenance. Developed
in the 1950’s and onward, SF6 circuit
breakers are widely used in electrical
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Super Grid

Superconducting electric
machine

A super grid is a wide area transmission
network that makes it possible to trade
high volumes of electricity across great
distances. It is sometimes also referred
to as a “mega grid”.

Superconducting electric machines are
electromechanical systems that rely on
the use of one or more superconducting
elements. Since superconductors have
no DC resistance, they typically have
greater efficiency. The most important
parameter that is of utmost interest
in superconducting machine is the
generation of a very high magnetic field
that is not possible in a conventional
machine.

Superconductivity
Supercomputer
A supercomputer is a computer with a
high level of performance compared to a
general-purpose computer. Performance
of a supercomputer is measured in
floating-point operations per second
(FLOPS) instead of million instructions
per second (MIPS). As of 2017, there
are supercomputers which can perform
up to nearly a hundred quadrillions of
FLOPS, measured in P (eta) FLOPS. As of
November 2017, all of the world’s fastest
500 supercomputers run Linux-based
operating systems. Additional, state of
the art research is being conducted in
China, United States, European Union,
Taiwan and Japan to build even faster,
more powerful and more technologically
superior exascale supercomputers.

Superconductivity is a phenomenon
of exactly zero electrical resistance
and expulsion of magnetic flux fields
occurring in certain materials, called
superconductors, when cooled below a
characteristic critical temperature. It was
discovered by Dutch physicist Heike
Kamerlingh Onnes on April 8, 1911, in
Leiden. Like ferromagnetism and atomic
spectral lines, superconductivity is a
quantum mechanical phenomenon.

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Superfluid
Superfluidity is the characteristic
property of a fluid with zero viscosity
which therefore flows without loss of
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kinetic energy. When stirred, a superfluid
forms cellular vortices that continue to
rotate indefinitely. Superfluidity occurs
in two isotopes of helium (helium-3 and
helium-4) when they are liquified by
cooling to cryogenic temperatures. It is
also a property of various other exotic
states of matter theorized to exist in
astrophysics, high-energy physics, and
theories of quantum gravity.

Superposition theorem

Superheterodyne receiver

Supervisory control and
data acquisition (SCADA)

A superheterodyne receiver, often
shortened to superhet, is a type of radio
receiver that uses frequency mixing to
convert a received signal to a fixed
intermediate frequency (IF) which
can be more conveniently processed
than the original carrier frequency. It
was invented by US engineer Edwin
Armstrong in 1918 during World War
I. Virtually all modern radio receivers
use the superheterodyne principle.

The superposition theorem for electrical
circuit’s states that for a linear system
the response (voltage or current) in
any branch of a bilateral linear circuit
having more than one independent
source equals the algebraic sum of the
responses caused by each independent
source acting alone, where all the other
independent sources are replaced by
their internal impedances.

Supervisory control and data acquisition
(SCADA) is a control system architecture
that uses computers, networked
data communications and graphical
user interfaces for high-level process
supervisory management, but uses other
peripheral devices such as programmable
logic controllers and discrete PID
controllers to interface to the process
plant or machinery. The operator
interfaces which enable monitoring and
the issuing of process commands, such as
controller set point changes, are handled
through the SCADA computer system.
However, the real-time control logic or
controller calculations are performed by
networked modules which connect to
the field sensors and actuators.

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Surge arrester
A surge arrester is a device to protect
electrical equipment from over-voltage
transients caused by external (lightning)
or internal (switching) events. Also
called a surge protection device (SPD)
or transient voltage surge suppressor
(TVSS), this class of device is used to
protect equipment in power transmission
and distribution systems. (For consumer
equipment protection, different products
called surge protectors are used.) The
energy criterion for various insulation
material can be compared by impulse
ratio, the surge arrester should have
a low impulse ratio, so that a surge
incident on the surge arrester may
be bypassed to the ground instead of
passing through the apparatus.

Switch
In electrical engineering, a switch
is an electrical component that can
“make” or “break” an electrical circuit,
interrupting the current or diverting
it from one conductor to another. The
mechanism of a switch removes or
restores the conducting path in a circuit
when it is operated. It may be operated
manually, for example, a light switch or
a keyboard button, may be operated by
a moving object such as a door, or may
be operated by some sensing element
for pressure, temperature or flow.

Surge Protection
A surge protector (or surge suppressor or
surge diverter) is an appliance or device
designed to protect electrical devices
from voltage spikes. A surge protector
attempts to limit the voltage supplied
to an electric device by either blocking
or shorting to ground any unwanted
voltages above a safe threshold. This
article primarily discusses specifications
and components relevant to the type of
protector that diverts (shorts) a voltage
spike to ground; however, there is some
coverage of other methods.

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Switched reluctance motor
The switched reluctance motor (SRM)
is a type of stepper motor, an electric
motor that runs by reluctance torque.
Unlike common DC motor types,
power is delivered to windings in the
stator (case) rather than the rotor. This
greatly simplifies mechanical design as
power does not have to be delivered
to a moving part, but it complicates

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the electrical design as some sort of
switching system needs to be used to
deliver power to the different windings.

Switched-mode power
supply
A switched-mode power supply
(switching-mode power supply,
switch-mode power supply, switched
power supply, SMPS, or switcher)
is an electronic power supply that
incorporates a switching regulator to
convert electrical power efficiently. Like
other power supplies, an SMPS transfers
power from a DC or AC source (often
mains power) to DC loads, such as a
personal computer, while converting
voltage and current characteristics.

de-energize equipment to allow work to
be done and to clear faults downstream.
This type of equipment is directly linked
to the reliability of the electricity supply.

Symbolic Circuit Analysis
Symbolic circuit analysis is a formal
technique of circuit analysis to
calculate the behavior or characteristic
of an electric/electronic circuit with
the independent variables (time or
frequency), the dependent variables
(voltages and currents), and (some or
all of) the circuit elements represented
by symbols.

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Symmetrical Components
Switchgear
In an electric power system, switchgear is
the combination of electrical disconnect
switches, fuses or circuit breakers used
to control, protect and isolate electrical
equipment. Switchgear is used both to

In electrical engineering, the method
of symmetrical components simplifies
analysis of unbalanced three-phase
power systems under both normal and
abnormal conditions. The basic idea is
that an asymmetrical set of N phasors can
be expressed as a linear combination of

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N symmetrical sets of phasors by means
of a complex linear transformation. In
the most common case of three-phase
systems, the resulting “symmetrical”
components are referred to as direct (or
positive), inverse (or negative) and zero
(or homopolar) linearly independent if
the circuit itself is balanced.

matching the speed and frequency of a
generator or other source to a running
network. An AC generator cannot
deliver power to an electrical grid unless
it is running at the same frequency as
the network. If two segments of a grid
are disconnected, they cannot exchange
AC power again until they are brought
back into exact synchronization.

Synchro
A synchro (also known as Selsyn and
by other brand names) is, in effect, a
transformer whose primary-to-secondary
coupling may be varied by physically
changing the relative orientation of the
two windings. Synchros are often used
for measuring the angle of a rotating
machine such as an antenna platform.
In its general physical construction, it
is much like an electric motor.

Synchronous Circuit
A synchronous circuit is a digital circuit
in which the changes in the state of
memory elements are synchronized by
a clock signal. In a sequential digital
logic circuit, data is stored in memory
devices called flip-flops or latches. The
output of a flip-flop is constant until
a pulse is applied to its “clock” input,
upon which the input of the flip-flop
is latched into its output.

Synchronization
(Alternating Current)
In an alternating current electric power
system, synchronization is the process of
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Synchronous Motor

Synchroscope

A synchronous electric motor is an AC
motor in which, at steady state, the
rotation of the shaft is synchronized
with the frequency of the supply current;
the rotation period is exactly equal
to an integral number of AC cycles.
Synchronous motors contain multiphase
AC electromagnets on the stator of the
motor that create a magnetic field which
rotates in time with the oscillations of
the line current.

In AC electrical power systems, a
synchroscope is a device that indicates
the degree to which two systems
(generators or power networks) are
synchronized with each other. For two
electrical systems to be synchronized,
both systems must operate at the same
frequency, and the phase angle between
the systems must be zero (and two
polyphase systems must have the same
phase sequence).

Syncom
Synchronous Rectification

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Active rectification, or synchronous
rectification, is a technique for
improving the efficiency of rectification
by replacing diodes with actively
controlled switches such as transistors,
usually power MOSFETs or power BJTs.
Historically, vibrator driven switches or
motor-driven commutators have also
been used for mechanical rectifiers and
synchronous rectification.

Syncom
(for
“synchronous
communication satellite”) started
as a 1961 NASA program for active
geosynchronous communication
satellites, all of which were developed
and manufactured by Hughes Space
and Communications. Syncom 2,
launched in 1963, was the world’s
first geosynchronous communications
satellite. Syncom 3, launched in 1964,
was the world’s first geostationary
satellite.

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System Identification
The field of system identification Note
a uses statistical methods to build
mathematical models of dynamical
systems from measured data. System
identification also includes the optimal
design of experiments for efficiently
generating informative data for fitting
such models as well as model reduction.

robot, automotive etc. It may integrate
digital and analog functions on a single
board. A typical application is in the
area of embedded systems.

System on a Chip
A system on a chip or system on chip
(SoC or SOC) is an integrated circuit
(also known as an “IC” or “chip”) that
integrates all components of a computer
or other electronic systems. It may
contain digital, analog, mixed-signal,
and often radio-frequency functions—
all on a single substrate. SoCs are very
common in the mobile computing
market because of their low power
consumption. A typical application is
in the area of embedded systems.

Systems Analysis
The Merriam-Webster dictionary defines
system analysis as “the process of
studying a procedure or business in
order to identify its goals and purposes
and create systems and procedures that
will achieve them in an efficient way”.
Another view sees system analysis as a
problem-solving technique that breaks
down a system into its component pieces
for the purpose of the studying how
well those component parts work and
interact to accomplish their purpose.

Systems software

System on Module
A system on a module (SOM) is a boardlevel circuit that integrates a system
function in a single module. This is
analogous to a system as referred to
in the life sciences as in the human
body - digestive-system, and nervous
system that go to form functional
humans or organisms. The organism
being an equivalent of a computer,

System software is software designed to
provide a platform for other software.
Examples of system software include
operating systems like macOS, GNU/
Linux , Android and Microsoft Windows,
computational science software,
game engines, industrial automation,
and software as a service applications.

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Tt
Tablet computer
A tablet computer, commonly shortened
to tablet, is a mobile device, typically
with a mobile operating system and
touchscreen display processing circuitry,
and a rechargeable battery in a single,
thin and flat package.

Tap Changer
A tap changer is a mechanism in
transformers which allows for variable
turn ratios to be selected in discrete
steps. Transformers with this mechanism
obtain this variable turn ratio by
connecting to a number of access points
known as taps along either the primary
or secondary winding. These systems
usually possess 33 taps (one at centre
“Rated” tap and sixteen to increase and
decrease the turn ratio) and allow for
±10% variation (each step providing
0.625% variation) from the nominal
transformer rating which, in turn, allows
for stepped voltage regulation of the
output.

Tachometer

T

A tachometer is an instrument measuring
the rotation speed of a shaft or disk,
as in a motor or other machine. The
device usually displays the revolutions
per minute (RPM) on a calibrated
analogue dial, but digital displays are
increasingly common. Essentially the
words tachometer and speedometer
have identical meaning: a device that
measures speed. It is by arbitrary
convention that in the automotive world
one is used for engine and the other for
vehicle speed. In formal engineering
nomenclature, more precise terms are
used to distinguish the two.

Tandem
Tandem is a language exchange app on
iOS and Android that connects language

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is the act and discipline of composing
drawings that visually communicate how
something functions or is constructed.

learners with native speakers. Members
can search for language exchange
partners to talk to by either text or
voice chat.

Taylor Series
In mathematics, a Taylor series is a
representation of a function as an infinite
sum of terms that are calculated from
the values of the function’s derivatives
at a single point. The concept of a
Taylor series was formulated by the
Scottish mathematician James Gregory
and formally introduced by the English
mathematician Brook Taylor in 1715. If
the Taylor series is centered at zero, then
that series is also called a Maclaurin
series, named after the Scottish
mathematician Colin Maclaurin, who
made extensive use of this special case
of Taylor series in the 18th century.

Technology
Technology is the collection of techniques,
skills, methods, and processes used in
the production of goods or services or in
the accomplishment of objectives, such
as scientific investigation. Technology
can be the knowledge of techniques,
processes, and the like, or it can be
embedded in machines to allow for
operation without detailed knowledge
of their workings.

T

Technical Drawing
Technical drawing, drafting or drawing,
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Telecommunication
Telecommunication is the transmission
of signs, signals, messages, words,
writings, images and sounds or
information of any nature by wire,
radio, optical or other electromagnetic
systems. Telecommunication occurs
when the exchange of information
between communication participants
includes the use of technology. It is
transmitted either electrically over
physical media, such as cables, or via
electromagnetic radiation.

Telecommunications
Industry Association

Telecommunications Cable

T

to strategic mass developments.
A telecommunication engineer is
responsible for designing and overseeing
the installation of telecommunications
equipment and facilities, such as complex
electronic switching systems, and other
plain old telephone service facilities,
optical fiber cabling, IP networks, and
microwave transmission systems.

Telecommunications cables are a type of
guided transmission mediums. Cables
are usually known to transmit electric
energy (AC/DC); however, cables in
telecommunications fields are used to
transmit electromagnetic waves; they
are called electromagnetic wave guides.

Telecommunications
Engineering
Telecommunications engineering is
an engineering discipline centered on
electrical and computer engineering
which seeks to support and enhance
telecommunication systems. The
work ranges from basic circuit design

The Telecommunications Industry
Association (TIA) is accredited by
the American National Standards
Institute (ANSI) to develop voluntary,
consensus-based industry standards
for a wide variety of Information and
Communication Technologies (ICT)
products, and currently represents nearly
400 companies. TIA’s Standards and
Technology Department operates twelve
engineering committees, which develop
guidelines for private radio equipment,
cellular towers, data terminals, satellites,
telephone terminal equipment,
accessibility, VoIP devices, structured
cabling, data centers, mobile device
communications, multimedia multicast,
vehicular telematics, healthcare ICT,

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machine to machine communications,
and smart utility networks.

are used to deliver landline telephone
service and Digital subscriber line (DSL)
phone cable service to the premises.
Telephone overhead lines are connected
to the public switched telephone
network.

Telegraph
Telegraphy is the long-distance
transmission of textual or symbolic (as
opposed to verbal or audio) messages
without the physical exchange of
an object bearing the message. Thus
semaphore is a method of telegraphy,
whereas pigeon post is not.

Telephone
A telephone, or phone, is a
telecommunications device that
permits two or more users to conduct
a conversation when they are too far
apart to be heard directly. A telephone
converts sound, typically and most
efficiently the human voice, into
electronic signals that are transmitted
via cables and other communication
channels to another telephone which
reproduces the sound to the receiving
user.

Telephone Line

T

A telephone line or telephone circuit
(or just line or circuit within the
industry) is a single-user circuit on a
telephone communication system. This
is the physical wire or other signaling
medium connecting the user’s telephone
apparatus to the telecommunications
network, and usually also implies a single
telephone number for billing purposes
reserved for that user. Telephone lines
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Television
Television (TV) is a telecommunication
medium used for transmitting moving
images in monochrome (black and
white), or in colour, and in two or three
dimensions and sound. The term can
refer to a television set, a television
program (“TV show”), or the medium
of television transmission. Television
is a mass medium for entertainment,
education, news, politics, gossip and
advertising.

Tensile Strength

T

Ultimate tensile strength (UTS),
often shortened to tensile strength
(TS), ultimate strength, or Ftu within
equations is the capacity of a material
or structure to withstand loads tending
to elongate, as opposed to compressive
strength, which withstands loads tending
to reduce size. In other words, tensile
strength resists tension (being pulled
apart), whereas compressive strength
resists compression (being pushed
together). Ultimate tensile strength is
measured by the maximum stress that
a material can withstand while being
stretched or pulled before breaking.
In the study of strength of materials,
tensile strength, compressive strength,
and shear strength can be analyzed
independently.

Tensile Stress
In continuum mechanics, stress is a
physical quantity that expresses the
internal forces that neighboring particles
of a continuous material exert on each
other, while strain is the measure of
the deformation of the material. For
example, when a solid vertical bar
is supporting a weight, each particle
in the bar pushes on the particles
immediately below it. When a liquid
is in a closed container under pressure,
each particle gets pushed against by
all the surrounding particles. The
container walls and the pressureinducing surface (such as a piston) push
against them in (Newtonian) reaction.
These macroscopic forces are actually
the net result of a very large number
of intermolecular forces and collisions
between the particles in those molecules.
Stress is frequently represented by a
lowercase Greek letter sigma (σ).

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Tesla (Unit)
The tesla (symbol T) is a derived unit
of magnetic flux density (informally,
magnetic field strength) in the
International System of Units. One
tesla is equal to one weber per square
metre. The unit was announced during
the General Conference on Weights
and Measures in 1960 and is named
in honour of Nikola Tesla, upon the
proposal of the Slovenian electrical
engineer France Avčin.

Tesla Coil
A Tesla coil is an electrical resonant
transformer circuit designed by inventor
Nikola Tesla in 1891. It is used to
produce high-voltage, low-current, high
frequency alternating-current electricity.
Tesla experimented with a number
of different configurations consisting
of two, or sometimes three, coupled
resonant electric circuits.

grid tube and the beam tetrode. In
screen-grid tubes and beam tetrodes,
the first grid is the control grid and the
second grid is the screen grid. In other
tetrodes one of the grids is a control
grid, while the other may have a variety
of functions.

Thermal Conductivity
Thermal conductivity is the property
of a material to conduct heat. It is
evaluated primarily in terms of the
Fourier’s Law for heat conduction. In
general, thermal conductivity is a tensor
property, expressing the anisotropy of
the property. Heat transfer occurs at a
lower rate in materials of low thermal
conductivity than in materials of high
thermal conductivity.

Thermal Expansion

Tetrode
A tetrode is a vacuum tube (called
valve in British English) having four
active electrodes. The four electrodes in
order from the centre are: a thermionic
cathode, first and second grids and a
plate (called anode in British English).
There are several varieties of tetrodes,
the most common being the screen-

Thermal expansion is the tendency
of matter to change in shape, area,
and volume in response to a change
in temperature. Temperature is a
monotonic function of the average
molecular kinetic energy of a substance.
When a substance is heated, the kinetic
energy of its molecules increases. Thus,
the molecules begin vibrating/moving
more and usually maintain a greater
average separation.

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as inrush current limiters, temperature
sensors (Negative Temperature
Coefficient or NTC type typically),
self-resetting overcurrent protectors,
and self-regulating heating elements
(Positive Temperature Coefficient or
PTC type typically).

Thermionic Emission
Thermionic emission is the thermally
induced flow of charge carriers from
a surface or over a potential-energy
barrier. This occurs because the thermal
energy given to the carrier overcomes
the work function of the material.
The charge carriers can be electrons
or ions, and in older literature are
sometimes referred to as “thermions”.
After emission, a charge that is equal
in magnitude and opposite in sign to
the total charge emitted is initially left
behind in the emitting region.

Thermocouple
A thermocouple is an electrical device
consisting of two dissimilar electrical
conductors forming electrical junctions at
differing temperatures. A thermocouple
produces a temperature-dependent
voltage as a result of the thermoelectric
effect, and this voltage can be interpreted
to measure temperature. Thermocouples
are a widely used type of temperature
sensor.

T

Thermistor
A thermistor is a type of resistor whose
resistance is dependent on temperature,
more so than in standard resistors. The
word is a portmanteau of thermal and
resistor. Thermistors are widely used

Thermodynamics
Thermodynamics is a branch of physics
concerned with heat and temperature
and their relation to other forms of
energy and work. The behavior of these

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quantities is governed by the four laws
of thermodynamics, irrespective of the
composition or specific properties of
the material or system in question. The
laws of thermodynamics are explained
in terms of microscopic constituents by
statistical mechanics. Thermodynamics
applies to a wide variety of topics in
science and engineering, especially
physical chemistry, chemical engineering
and mechanical engineering.

Thermostat
A thermostat is a component which
senses the temperature of a system
so that the system’s temperature is
maintained near a desired setpoint.
Thermostats are used in any device or
system that heats or cools to a setpoint
temperature, examples include building
heating, central heating, air conditioners,
HVAC systems, water heaters, as well as
kitchen equipment including ovens and
refrigerators and medical and scientific
incubators. In scientific literature, these
devices are often broadly classified as
thermostatically controlled loads (TCLs).

Thermoelectric Effect
The thermoelectric effect is the direct
conversion of temperature differences
to electric voltage and vice versa via a
thermocouple. A thermoelectric device
creates voltage when there is a different
temperature on each side. Conversely,
when a voltage is applied to it, it creates
a temperature difference. At the atomic
scale, an applied temperature gradient
causes charge carriers in the material
to diffuse from the hot side to the cold
side.

Third Rail
A third rail is a method of providing
electric power to a railway locomotive
or train, through a semi-continuous
rigid conductor placed alongside or
between the rails of a railway track.
It is used typically in a mass transit
or rapid transit system, which has
alignments in its own corridors, fully
or almost fully segregated from the
outside environment. Third rail systems
are always supplied from direct current
electricity.

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Three-phase AC Railway
Electrification
Three-phase AC railway electrification
was used in Italy, Switzerland and the
United States in the early twentieth
century. Italy was the major user, from
1901 until 1976, although lines through
two tunnels also used the system; the
Simplon Tunnel between Switzerland
and Italy from 1906 to 1930 (but not
connected to the Italian system), and the
Cascade Tunnel of the Great Northern
Railway in the United States from 1909
to 1939. The first standard gauge line
was in Switzerland, from Burgdorf to
Thun (40 km or 25 mi), since 1899.

power generation, transmission, and
distribution. It is a type of polyphase
system and is the most common method
used by electrical grids worldwide to
transfer power. It is also used to power
large motors and other heavy loads. A
three-wire three-phase circuit is usually
more economical than an equivalent twowire single-phase circuit at the same line
to ground voltage because it uses less
conductor material to transmit a given
amount of electrical power. Polyphase
power systems were independently
invented by Galileo Ferraris, Mikhail
Dolivo-Dobrovolsky, Jonas Wenström,
John Hopkinson and Nikola Tesla in
the late 1880s.

Three-phase Power
T

Three-phase Electric
Power
Three-phase electric power is a common
method of alternating current electric

Three-phase electric power is a common
method of alternating current electric
power generation, transmission, and
distribution. It is a type of polyphase
system and is the most common method
used by electrical grids worldwide to
transfer power. It is also used to power
large motors and other heavy loads. A
three-wire three-phase circuit is usually
more economical than an equivalent twowire single-phase circuit at the same line
to ground voltage because it uses less
conductor material to transmit a given

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amount of electrical power. Polyphase
power systems were independently
invented by Galileo Ferraris, Mikhail
Dolivo-Dobrovolsky, Jonas Wenström,
John Hopkinson and Nikola Tesla in
the late 1880s.

in some areas). A wye system allows
the use of two different voltages from
all three phases, such as a 230/400 V
system which provides 230 V between
the neutral (centre hub) and any one
of the phases, and 400 V across any
two phases. A delta system arrangement
only provides one voltage magnitude,
however it has a greater redundancy
as it may continue to operate normally
with one of the three supply windings
offline, albeit at 57.7% of total capacity.
Harmonic current in the neutral may
become very large if non-linear loads
are connected.

Trivalent element
One having three valence electrons.
Used as an impurity in semiconductor
material to produce p-type material.
Most commonly used trivalent elements
are: Aluminum, Gallium and Boron.

Thyristor

Three-phase
In electrical engineering, three-phase
electric power systems have at least
three conductors carrying alternating
current voltages that are offset in time
by one-third of the period. A threephase system may be arranged in delta
(∆) or star (Y) (also denoted as wye

A thyristor is a solid-state semiconductor
device with four layers of alternating Pand N-type materials. It acts exclusively
as a bistable switch, conducting when
the gate receives a current trigger,
and continuing to conduct while the
voltage across the device is not reversed
(forward-biased). A three-lead thyristor
is designed to control the larger current
of its two leads by combining that
current with the smaller current of its
other lead, known as its control lead. In
contrast, a two-lead thyristor is designed
to switch on if the potential difference
between its leads is sufficiently large
(breakdown voltage).

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computing in the 1970s represented a
major technological shift in the history
of computing.

Time-invariant system

Tidal power
Tidal power or tidal energy is a form
of hydropower that converts the energy
obtained from tides into useful forms
of power, mainly electricity. Although
not yet widely used, tidal energy has
potential for future electricity generation.
Tides are more predictable than the
wind and the sun. Among sources of
renewable energy, tidal energy has
traditionally suffered from relatively
high cost and limited availability of
sites with sufficiently high tidal ranges
or flow velocities, thus constricting its
total availability.

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Time sharing

A time-invariant (TIV) system has a
time-dependent system function that
is not a direct function of time. Such
systems are regarded as a class of
systems in the field of system analysis.
The time-dependent system function is
a function of the time-dependent input
function. If this function depends only
indirectly on the time-domain (via the
input function, for example), then that
is a system that would be considered
time-invariant. Conversely, any direct
dependence on the time-domain of the
system function could be considered as
a “time-varying system”.

Tin
Tin is a chemical element with symbol
Sn (from Latin: stannum) and atomic
number 50. It is a post-transition metal
in group 14 of the periodic table. It
is obtained chiefly from the mineral
cassiterite, which contains tin dioxide,
SnO2. Tin shows a chemical similarity
to both of its neighbors in group 14,
germanium and lead, and has two main
oxidation states, +2 and the slightly more
stable +4. Tin is the 49th most abundant
element and has, with 10 stable isotopes,
the largest number of stable isotopes in
the periodic table, thanks to its magic
number of protons.

In computing, time-sharing is the sharing
of a computing resource among many
users by means of multiprogramming
and multi-tasking at the same time.
Its introduction in the 1960s and
emergence as the prominent model of
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Topology (Electrical
Circuits)

Torque

The topology of an electronic circuit
is the form taken by the network
of interconnections of the circuit
components. Different specific values or
ratings of the components are regarded
as being the same topology. Topology is
not concerned with the physical layout
of components in a circuit, nor with
their positions on a circuit diagram. It
is only concerned with what connections
exist between the components. There
may be numerous physical layouts and
circuit diagrams that all amount to the
same topology.

Toroidal Inductors and
Transformers
Toroidal inductors and transformers are
inductors and transformers which use
magnetic cores with a toroidal (ring
or donut) shape. They are passive
electronic components, consisting of a
circular ring or donut shaped magnetic
core of ferromagnetic material such as
laminated iron, iron powder, or ferrite,
around which wire is wound.

Torque, moment, or moment of force
is rotational force. Just as a linear
force is a push or a pull, a torque can
be thought of as a twist to an object.
In three dimensions, the torque is a
pseudovector; for point particles, it
is given by the cross product of the
position vector (distance vector) and
the force vector.

Total harmonic Distortion
(THD)
The total harmonic distortion (THD)
is a measurement of the harmonic
distortion present in a signal and is
defined as the ratio of the sum of the
powers of all harmonic components to
the power of the fundamental frequency.
Distortion factor, a closely related term,
is sometimes used as a synonym. In
audio systems, lower distortion means
the components in a loudspeaker,
amplifier or microphone or other
equipment produce a more accurate
reproduction of an audio recording.

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Traction Motor
A traction motor is an electric motor
used for propulsion of a vehicle, such
as an electric locomotive or electric
roadway vehicle. Traction motors
are used in electrically powered rail
vehicles (electric multiple units) and
other electric vehicles including electric
milk floats, elevators, conveyors, and
trolleybuses, as well as vehicles with
electrical transmission systems (dieselelectric, electric hybrid vehicles), and
battery electric vehicles.

Traction Substation

T

A traction substation or traction current
converter plant is an electrical substation
that converts electric power from the
form provided by the electrical power
industry for public utility service to an
appropriate voltage, current type and
frequency to supply railways, trams
(streetcars) or trolleybuses with traction
current.

Transatlantic
Communications Cable
A transatlantic telecommunications
cable is a submarine communications
cable connecting one side of the Atlantic
Ocean to the other. In the 19th and early
20th centuries each cable was a single
wire. After mid-century, coaxial cable
came into use, with amplifiers. Late in
the century, all used optical fiber, and
most now use optical amplifiers.

Transatlantic Telegraph
Cable
A transatlantic telegraph cable is an
undersea cable running under the
Atlantic Ocean used for telegraph
communications. The first was laid across
the floor of the Atlantic from Telegraph
Field, Foilhommerum Bay, Valentia
Island in western Ireland to Heart’s
Content in eastern Newfoundland. The
first communications occurred August
16, 1858, reducing the communication
time between North America and
Europe from ten days – the time it took
to deliver a message by ship – to only
17 hours. Transatlantic telegraph cables
have been replaced by transatlantic
telecommunications cables.

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Transceiver
A transceiver is a device comprising
both a transmitter and a receiver that
are combined and share common
circuitry or a single housing. When no
circuitry is common between transmit
and receive functions, the device is a
transmitter-receiver. The term originated
in the early 1920s. Similar devices
include transponders, transverters, and
repeaters.

Transfer Function
In engineering, a transfer function (also
known as system function or network
function) of an electronic or control
system component is a mathematical
function giving the corresponding
output value for each possible value
of the input to the device. It is often
represented as a graph, called a transfer
curve or characteristic curve. The
transfer function provides information
which specifies the behavior of the
component in a system, and is used in
the mathematical analysis of systems,
particularly using the block diagram
technique, in electronics and control
theory.

Transducers
A transducer is a device that converts
energy from one form to another.
Usually a transducer converts a signal
in one form of energy to a signal in
another. Transducers are often employed
at the boundaries of automation,
measurement, and control systems,
where electrical signals are converted
to and from other physical quantities
(energy, force, torque, light, motion,
position, etc.). The process of converting
one form of energy to another is known
as transduction.

Transformer Oil Testing
Transformer oil, a type of insulating and
cooling oil used in transformers and
other electrical equipment, needs to be
tested periodically to ensure that it is
still fit for purpose. This is because it
tends to deteriorate over time. Testing
sequences and procedures are defined
by various international standards,
many of them set by ASTM. Testing
consists of measuring breakdown
voltage and other physical and chemical
properties of samples of the oil, either

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in a laboratory or using portable test
equipment on site.

Transformer

Transformer Oil
Transformer oil or insulating oil is an
oil that is stable at high temperatures
and has excellent electrical insulating
properties. It is used in oil-filled
transformers, some types of high-voltage
capacitors, fluorescent lamp ballasts,
and some types of high-voltage switches
and circuit breakers. Its functions are
to insulate, suppress corona discharge
and arcing, and to serve as a coolant.
Transformer oil is most often based on
mineral oil, but alternative formulations
with better engineering or environmental
properties are growing in popularity.

A transformer is an electrical device that
transfers electrical energy between two
or more circuits through electromagnetic
induction. A varying current in one coil
of the transformer produces a varying
magnetic field, which in turn induces
a varying electromotive force (emf) or
“voltage” in a second coil. Power can
be transferred between the two coils
through the magnetic field, without a
metallic connection between the two
circuits. Faraday’s law of induction
discovered in 1831 described this effect.
Transformers are used to increase or
decrease the alternating voltages in
electric power applications.

T

Transformer Types
A variety of types of electrical transformer
are made for different purposes. Despite
their design differences, the various
types employ the same basic principle as
discovered in 1831 by Michael Faraday,
and share several key functional parts.
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Transient Response
In electrical engineering and mechanical
engineering, a transient response or
natural response is the response of a
system to a change from an equilibrium
or a steady state. The transient response
is not necessarily tied to abrupt events
but to any event that affects the
equilibrium of the system. The impulse
response and step response are transient
responses to a specific input (an impulse
and a step, respectively).

Transmission
(Telecommunications)
In telecommunications, transmission is
the process of sending and propagating
an analogue or digital information signal
over a physical point-to-point or pointto-multipoint transmission medium,
either wired, optical fiber or wireless.

Transistor
A transistor is a semiconductor device
used to amplify or switch electronic
signals and electrical power. It is
composed of semiconductor material
usually with at least three terminals
for connection to an external circuit. A
voltage or current applied to one pair
of the transistor’s terminals controls
the current through another pair of
terminals. Because the controlled
(output) power can be higher than the
controlling (input) power, a transistor
can amplify a signal. Today, some
transistors are packaged individually,
but many more are found embedded
in integrated circuits.

T

Transmission Line
In communications and electronic
engineering, a transmission line is a
specialized cable or other structure
designed to conduct alternating current
of radio frequency, that is, currents
with a frequency high enough that
their wave nature must be taken into
account. Transmission lines are used

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for purposes such as connecting radio
transmitters and receivers with their
antennas (they are then called feed lines
or feeders), distributing cable television
signals, trunklines routing calls between
telephone switching centres, computer
network connections and high speed
computer data buses.

Transmission Tower
A transmission tower or power tower
(electricity pylon in the United Kingdom,
Canada and parts of Europe) is a tall
structure, usually a steel lattice tower,
used to support an overhead power line.
They are used in high-voltage AC and
DC systems, and come in a wide variety
of shapes and sizes. Typical height
ranges from 15 to 55 m (49 to 180 ft),
though the tallest are the 370 m (1,214
ft) towers of a 2,700 m (8,858 ft) span
of Zhoushan Island Overhead Powerline
Tie. In addition to steel, other materials
may be used, including concrete and
wood.

Transmission System
Operator
A transmission system operator (TSO)
is an entity entrusted with transporting
energy in the form of natural gas or
electrical power on a national or
regional level, using fixed infrastructure.
The term is defined by the European
Commission. The certification procedure
for Transmission System Operators is
listed in Article 10 of the Electricity and
Gas Directives of 2009.
T

Transmitter
In electronics and telecommunications
a transmitter or radio transmitter is an
electronic device which produces radio
waves with an antenna. The transmitter
itself generates a radio frequency
alternating current, which is applied
to the antenna. When excited by this
alternating current, the antenna radiates
radio waves.
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used on the 1886 Benz automobile, and
were used on the Model T until 1927.

Traveling-wave Tube
A traveling-wave tube (TWT, pronounced
“twit”) or traveling-wave tube amplifier
(TWTA, pronounced “tweeta”) is a
specialized vacuum tube that is used
in electronics to amplify radio frequency
(RF) signals in the microwave range. The
TWT belongs to a category of “linear
beam” tubes, such as the klystron,
in which the radio wave is amplified
by absorbing power from a beam of
electrons as it passes down the tube.

TRIAC
TRIAC, from triode for alternating
current, is a generic trademark for a
three terminal electronic component
that conducts current in either direction
when triggered. Its formal name is
bidirectional triode thyristor or bilateral
triode thyristor. A thyristor is analogous
to a relay in that a small voltage and
current can control a much larger
voltage and current. The illustration
on the right shows the circuit symbol
for a TRIAC where A1 is Anode 1, A2
is Anode 2, and G is Gate. Anode 1
and Anode 2 are normally termed Main
Terminal 1 (MT1) and Main Terminal 2
(MT2) respectively.

Trembler Coil

T

A trembler coil or vibrator coil is
a type of high-voltage ignition coil
used in the ignition system of early
automobiles, most notably the Benz
Patent-Motorwagen and the Ford
Model T. Its distinguishing feature is a
vibrating magnetically-activated contact
called a trembler or interrupter, which
breaks the primary current, generating
multiple sparks during each cylinder’s
power stroke. Trembler coils were first
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Triangle Wave
A triangle wave is a non-sinusoidal
waveform named for its triangular
shape. It is a periodic, piecewise linear,
continuous real function. Like a square
wave, the triangle wave contains only
odd harmonics. However, the higher
harmonics roll off much faster than
in a square wave (proportional to the
inverse square of the harmonic number
as opposed to just the inverse).

English) consisting of three electrodes
inside an evacuated glass envelope: a
heated filament or cathode, a grid, and
a plate (anode). Developed from Lee De
Forest’s 1906 Audion, a partial vacuum
tube that added a grid electrode to the
thermionic diode (Fleming valve), the
triode was the first practical electronic
amplifier and the ancestor of other types
of vacuum tubes such as the tetrode
and pentode. Its invention founded
the electronics age, making possible
amplified radio technology and longdistance telephony.

Trigger Transformer
A Trigger transformer is a small,
usually ferrite cored transformer used
in applications requiring a high voltage
pulse, typically to start ionization of a
gas to allow a current to pass.

T

Triode

Trolley Pole
A trolley pole is a tapered cylindrical
pole of wood or metal, used to transfer
electricity from a “live” overhead wire
to the control and the electric traction
motors of a tram or trolley bus. It is
a type of current collector. The use of
overhead wire in a system of current
collection is reputed to be the 1880
invention of Frank J. Sprague, but the
first working trolley pole was developed
and demonstrated by Charles Van
Depoele, in autumn 1885.

A triode is an electronic amplifying
vacuum tube (or valve in British
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radiation, crosstalk between neighboring
pairs and improves rejection of external
electromagnetic interference. It was
invented by Alexander Graham Bell.

Trolleybus
A trolleybus (also known as trolley bus,
trolley coach, trackless trolley, trackless
tram [in early years] or trolley) is an
electric bus that draws power from
overhead wires (generally suspended
from roadside posts) using springloaded trolley poles. Two wires and
poles are required to complete the
electrical circuit. This differs from a tram
or streetcar, which normally uses the
track as the return path, needing only
one wire and one pole (or pantograph).

Twisted Pair
Twisted pair cabling is a type of wiring
in which two conductors of a single
circuit are twisted together for the
purposes of improving electromagnetic
compatibility. Compared to a single
conductor or an untwisted balanced pair,
a twisted pair reduces electromagnetic

Two-phase Electric Power
Two-phase electrical power was an
early 20th-century polyphase alternating
current electric power distribution
system. Two circuits were used, with
voltage phases differing by one-quarter
of a cycle, 90°. Usually circuits used
four wires, two for each phase. Less
frequently, three wires were used, with
a common wire with a larger-diameter
conductor. Some early two-phase
generators had two complete rotor
and field assemblies, with windings
physically offset to provide two-phase
power. The generators at Niagara
Falls installed in 1895 were the largest
generators in the world at that time and
were two-phase machines. Three-phase
systems eventually replaced the original
two-phase power systems for power
transmission and utilization. There
remain few two-phase distribution
systems, with examples in Philadelphia,

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Pennsylvania; many buildings in Center
City are permanently wired for twophase and Hartford, Connecticut.

Two-port Network
A two-port network is an electrical
network (circuit) or device with two
pairs of terminals to connect to external
circuits. Two terminals constitute a port
if the currents applied to them satisfy
the essential requirement known as
the port condition: the electric current
entering one terminal must equal
the current emerging from the other
terminal on the same port. The ports
constitute interfaces where the network
connects to other networks, the points
where signals are applied or outputs
are taken. In a two-port network, often
port 1 is considered the input port and
port 2 is considered the output port.

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Uu
Ubiquitous Computing
Ubiquitous computing is a concept in
software engineering and computer
science where computing is made
to appear anytime and everywhere.
In contrast to desktop computing,
ubiquitous computing can occur using
any device, in any location, and in
any format. A user interacts with the
computer, which can exist in many
different forms, including laptop
computers, tablets and terminals in
everyday objects such as a refrigerator
or a pair of glasses. The underlying
technologies to support ubiquitous
computing include Internet, advanced
middleware, operating system, mobile
code, sensors, microprocessors, new I/O
and user interfaces, networks, mobile
protocols, location and positioning, and
new materials.

scheme of operation (rotation or linear
translation). Ultrasonic motors differ
from piezoelectric actuators in several
ways, though both typically use some
form of piezoelectric material, most often
lead zirconate titanate and occasionally
lithium niobate or other single-crystal
materials.

Ultrasonics
Ultrasound is sound waves with
frequencies higher than the upper audible
limit of human hearing. Ultrasound is
no different from ‘normal’ (audible)
sound in its physical properties, except
in that humans cannot hear it. This limit
varies from person to person and is
approximately 20 kilohertz (20,000 hertz)
in healthy, young adults. Ultrasound
devices operate with frequencies from
20 kHz up to several gigahertz.

U

Ultrasonic Motor
An ultrasonic motor is a type of electric
motor powered by the ultrasonic
vibration of a component, the stator,
placed against another component,
the rotor or slider depending on the

Undersampling
In signal processing, undersampling or
bandpass sampling is a technique where
one samples a bandpass-filtered signal

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at a sample rate below its Nyquist rate
(twice the upper cutoff frequency), but
is still able to reconstruct the signal.

copper tube encasing the rotor or rods
embedded in the rotor).

Unix
Unijunction transistor
A unijunction transistor (UJT) is a
three-lead electronic semiconductor
device with only one junction that acts
exclusively as an electrically controlled
switch.

Unix is a family of multitasking,
multiuser computer operating systems
that derive from the original AT&T
Unix, development starting in the 1970s
at the Bell Labs research center by Ken
Thompson, Dennis Ritchie, and others.

Unshielded Twisted Pair

U

Unipolar Motor
A unipolar motor is a direct current
(DC) motor typically with slip-rings
on each end of a cylindrical rotor and
field magnets or a DC field winding
generating a magnetic field on the stator.
The rotor has typically not a winding
but just straight connections in axial
direction between the slip-rings (e.g. a

Unshielded twisted pair (UTP) cables are
found in many Ethernet networks and
telephone systems. For indoor telephone
applications, UTP is often grouped
into sets of 25 pairs according to a
standard 25-pair color code originally
developed by AT&T Corporation. A
typical subset of these colors (white/
blue, blue/white, white/orange, orange/
white) shows up in most UTP cables.
The cables are typically made with
copper wires measured at 22 or 24
American Wire Gauge (AWG), with the

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colored insulation typically made from
an insulator such as polyethylene or
FEP and the total package covered in
a polyethylene jacket.

Upsampling
In digital signal processing, upsampling
can refer to the entire process of
increasing the sampling rate of a
signal, or it can refer to just one step
of the process, the other step being
interpolation. Complementary to
decimation, which decreases sampling
rate, it is a specific case of sample rate
conversion in a multi-rate digital signal
processing system. When upsampling is
performed on a sequence of samples of
a signal or other continuous function,
it produces an approximation of the
sequence that would have been obtained
by sampling the signal at a higher
rate (or density, as in the case of a
photograph). For example, if compact
disc audio at 44,100 samples/second
is upsampled by a factor of 5/4, the
resulting sample-rate is 55,125.

Utility Frequency
The utility frequency, (power) line
frequency (American English) or
mains frequency (British English) is the
nominal frequency of the oscillations of
alternating current (AC) in an electric
power grid transmitted from a power
station to the end-user. In large parts
of the world this is 50 Hz, although
in the Americas and parts of Asia it
is typically 60 Hz. Current usage by
country or region is given in the list of
mains power around the world.

Utility Pole
A utility pole is a column or post used
to support overhead power lines and
various other public utilities, such as
electrical cable, fiber optic cable, and
related equipment such as transformers
and street lights. It can be referred to
as a transmission pole, telephone pole,
telecommunication pole, power pole,
hydro pole, telegraph pole, or telegraph
post, depending on its application. A
stobie pole is a multi-purpose pole made
of two steel joists held apart by a slab of
concrete in the middle, generally found
in South Australia.

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Vv

thermionic tube or thermionic valve
usually without a heater.

Vacuum Capacitor
A vacuum variable capacitor is a variable
capacitor which uses a high vacuum
as the dielectric instead of air or other
insulating material. This allows for a
higher voltage rating using a smaller
total volume. There are several different
designs in vacuum variables. The most
common form is inter-meshed concentric
cylinders, which are contained within
a glass or ceramic vacuum envelope,
similar to an electron tube. A metal
bellows is used to maintain a vacuum
seal while allowing positional control
for the moving parts of the capacitor.

Variable Capacitor
A variable capacitor is a capacitor whose
capacitance may be intentionally and
repeatedly changed mechanically or
electronically. Variable capacitors are
often used in L/C circuits to set the
resonance frequency, e.g. to tune a radio
(therefore it is sometimes called a tuning
capacitor or tuning condenser), or as a
variable reactance, e.g. for impedance
matching in antenna tuners.

Variable-frequency Drive
Vacuum tube
V

In electronics, a vacuum tube, an
electron tube, or just a tube (North
America), or valve (Britain and some
other regions) is a device that controls
electric current between electrodes in
an evacuated container. Vacuum tubes
mostly rely on thermionic emission
of electrons from a hot filament or a
heated cathode. This type is called a

A variable-frequency drive (VFD; also
termed adjustable-frequency drive,
“variable-voltage/variable-frequency
(VVVF) drive”, variable speed drive,
AC drive, micro drive or inverter drive)
is a type of adjustable-speed drive used
in electro-mechanical drive systems to
control AC motor speed and torque
by varying motor input frequency and
voltage.

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Varnish

Varicap
In electronics, a varicap diode, varactor
diode, variable capacitance diode,
variable reactance diode or tuning diode
is a type of diode designed to exploit
the voltage-dependent capacitance of a
reversed-biased p–n junction.

Varnish is a transparent, hard, protective
finish or film that is primarily used
in wood finishing but also for other
materials. Varnish is traditionally a
combination of a drying oil, a resin, and
a thinner or solvent. Varnish finishes are
usually glossy but may be designed to
produce satin or semi-gloss sheens by
the addition of “flatting” agents. Varnish
has little or no color, is transparent, and
has no added pigment, as opposed to
paints or wood stains, which contain
pigment and generally range from
opaque to translucent. Varnishes are
also applied over wood stains as a final
step to achieve a film for gloss and
protection. Some products are marketed
as a combined stain and varnish.

Varistor
A varistor is an electronic component
with an electrical resistance that varies
with the applied voltage. Also known
as a voltage-dependent resistor (VDR),
it has a nonlinear, non-ohmic current–
voltage characteristic that is similar to
that of a diode. In contrast to a diode
however, it has the same characteristic
for both directions of traversing current.
At low voltage it has a high electrical
resistance which decreases as the voltage
is raised.

V

Vector Control (Motor)
Vector control, also called field-oriented
control (FOC), is a variable-frequency

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drive (VFD) control method in which
the stator currents of a three-phase
AC electric motor are identified as
two orthogonal components that
can be visualized with a vector. One
component defines the magnetic flux
of the motor, the other the torque. The
control system of the drive calculates
the corresponding current component
references from the flux and torque
references given by the drive’s speed
control. Typically proportional-integral
(PI) controllers are used to keep the
measured current components at their
reference values.

Vector Group
In electrical engineering, a vector group
is the International Electrotechnical
Commission (IEC) method of
categorizing the high voltage (HV)
windings and low voltage (LV)
winding configurations of threephase transformers. The vector group
designation indicates the windings
configurations and the difference in
phase angle between them. For example,
a wye HV winding and delta LV winding
with a 30-degree lead is denoted as
Yd11.

Vehicle-to-grid

V

Vehicle-to-grid (V2G) describes a system
in which plug-in electric vehicles, such
as electric cars (BEV), plug-in hybrids
(PHEV) or hydrogen Fuel Cell Electric
Vehicles (FCEV), communicate with the
power grid to sell demand response
services by either returning electricity to
the grid or by throttling their charging
rate.

Vehicular Automation
Vehicular automation involves the use
of mechatronics, artificial intelligence,
and multi-agent system to assist a
vehicle’s operator. These features and
the vehicles employing them may be
labeled as intelligent or smart. A vehicle
using automation for difficult tasks,
especially navigation, may be referred to
as semi-autonomous. A vehicle relying
solely on automation is consequently
referred to as robotic or autonomous.
After the invention of the integrated
circuit, the sophistication of automation
technology increased. Manufacturers
and researchers subsequently added
a variety of automated functions to
automobiles and other vehicles.

Versorium
The versorium (Latin “turn around”)
was the first ever electroscope, the
first instrument that could detect the
presence of static electric charge. It was
invented in 1600 by William Gilbert,
physician to Queen Elizabeth I.

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Very-large-scale
Integration (VLSI)
Very-large-scale integration (VLSI) is the
process of creating an integrated circuit
(IC) by combining billions of transistors
into a single chip. VLSI began in the
1970s when complex semiconductor and
communication technologies were being
developed. The microprocessor is a VLSI
device. Before the introduction of VLSI
technology most ICs had a limited set
of functions they could perform. An
electronic circuit might consist of a CPU,
ROM, RAM and other glue logic. VLSI
lets IC designers add all of these into
one chip.

Video Camera Tube
The video camera tube was a type of
cathode ray tube used to capture the
television image prior to the introduction
of charge-coupled devices (CCDs) in the
1980s. Several different types of tubes
were in use from the early 1930s to
the 1980s.

Video Game Console
Vibrator (Electronic)
In electronics before the development
of switch-mode power supplies and the
introduction of semiconductor devices
operating off low voltage, there was
a requirement to generate voltages
of about 50 to 250V DC from vehicle
batteries. Electromechanical components
known as vibrators were used in a circuit
similar to modern solid state inverter
circuits to provide a pulsating DC which
could be converted to a higher voltage
with a transformer, rectified, and filtered
to create higher-voltage DC.

A video game console is an electronic,
digital or computer device that outputs
a video signal or visual image to display
a video game that one or more people
can play.

Virtual ground
In
electronics,
a
virtual
ground (or virtual earth) is a node of
a circuit that is maintained at a steady
reference potential, without being
connected directly to the reference
potential. In some cases the reference
potential is considered to be that of the

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surface of the earth, and the reference
node is called “ground” or “earth” as
a consequence.

Virtual Power Plant
A virtual power plant (VPP) is a
cloud-based distributed power plant
that aggregates the capacities of
heterogeneous Distributed Energy
Resources (DERs) for the purposes of
enhancing power generation, as well as
trading or selling power on the open
market. Examples of virtual power
plants exist in the United States, Europe,
and Australia.

thyristors, TRIACs, SCRs or IGBTs,
which converts a fixed voltage, fixed
frequency alternating current (AC)
electrical input supply to obtain
variable voltage in output delivered
to a resistive load. This varied voltage
output is used for dimming street lights,
varying heating temperatures in homes
or industry, speed control of fans and
winding machines and many other
applications, in a similar fashion to an
autotransformer.

Voltage converter
Volt
The volt (symbol: V) is the derived unit
for electric potential, electric potential
difference (voltage), and electromotive
force. It is named after the Italian
physicist Alessandro Volta (1745–1827).

A voltage converter is an electric power
converter which changes the voltage
of an electrical power source. It may
be combined with other components to
create a power supply.

V

Voltage division

Voltage controller
A voltage controller, also called an AC
voltage controller or AC regulator is
an electronic module based on either

In electronics, a voltage divider (also
known as a potential divider) is a
passive linear circuit that produces an

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output voltage (Vout) that is a fraction of
its input voltage (Vin). Voltage division
is the result of distributing the input
voltage among the components of the
divider. A simple example of a voltage
divider is two resistors connected in
series, with the input voltage applied
across the resistor pair and the output
voltage emerging from the connection
between them.

to the input current. Power gain is the
square of either voltage or current gain,
depending on which type of amplifier
it is (voltage or current).

Voltage regulation

Voltage doubler
A voltage doubler is an electronic circuit
which charges capacitors from the input
voltage and switches these charges in
such a way that, in the ideal case, exactly
twice the voltage is produced at the
output as at its input.

In electrical engineering, particularly
power engineering, voltage regulation
is a measure of change in the voltage
magnitude between the sending and
receiving end of a component, such
as a transmission or distribution line.
Voltage regulation describes the ability
of a system to provide near constant
voltage over a wide range of load
conditions. The term may refer to a
passive property that results in more
or less voltage drop under various load
conditions, or to the active intervention
with devices for the specific purpose of
adjusting voltage.

V

Voltage Gain
Voltage gain is the ratio of output
voltage to the input voltage, while the
current gain is the ratio of output current

Voltage regulator
A voltage regulator is an electronic
circuit that provides a stable DC
voltage independent of the load current,
temperature and AC line voltage
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variations. A voltage regulator may
use a simple feed-forward design or
may include negative feedback. It may
use an electromechanical mechanism, or
electronic components. Depending on
the design, it may be used to regulate
one or more AC or DC voltages.

spikes), or transferred energy (energy
spikes) in an electrical circuit.

Voltage

Voltage source
A voltage source is a two terminal device
which can maintain a fixed voltage.
An ideal voltage source can maintain
the fixed voltage independent of the
load resistance or the output current.
However, a real-world voltage source
cannot supply unlimited current. A
voltage source is the dual of a current
source. Real-world sources of electrical
energy, such as batteries, generators,
and power systems, can be modeled for
analysis purposes as a combination of
an ideal voltage source and additional
combinations of impedance elements.

Voltage, electric potential difference,
electric pressure or electric tension
(formally denoted ∆V or ∆U, but more
often simply as V or U, for instance
in the context of Ohm’s or Kirchhoff’s
circuit laws) is the difference in electric
potential between two points. The
voltage between two points is equal
to the work done per unit of charge
against a static electric field to move
a test charge between two points. This
is measured in units of volts (a joule
per coulomb); moving 1 coulomb of
charge across 1 volt of electric potential
requires 1 joule of work.

V

Voltage spike
In electrical engineering, spikes are fast,
short duration electrical transients in
voltage (voltage spikes), current (current

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Voltage-controlled
amplifier
A variable-gain or voltage-controlled
amplifier is an electronic amplifier that
varies its gain depending on a control
voltage (often abbreviated CV). VCAs
have many applications, including
audio level compression, synthesizers
and amplitude modulation.

Voltmeter
A voltmeter is an instrument used for
measuring electrical potential difference
between two points in an electric circuit.
Analog voltmeters move a pointer across
a scale in proportion to the voltage of
the circuit; digital voltmeters give a
numerical display of voltage by use of
an analog to digital converter.

Volt-ampere
A volt-ampere (VA) is the unit used
for the apparent power in an electrical
circuit, equal to the product of rootmean-square (RMS) voltage and RMS
current. In direct current (DC) circuits,
this product is equal to the real power
(active power) in watts. Volt-amperes are
useful only in the context of alternating
current (AC) circuits (sinusoidal voltages
and currents of the same frequency).

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WW

Wattmeter

War of Currents
The war of the currents (sometimes
called battle of the currents) was a series
of events surrounding the introduction
of competing electric power transmission
systems in the late 1880s and early 1890s.
It included commercial competition,
a debate over electrical safety, and
a media/propaganda campaign that
grew out of it, with the main players
being the direct current (DC) based
Edison Electric Light Company and
the alternating current (AC) based
Westinghouse Electric Company. It took
place during the introduction and rapid
expansion of the alternating current
standard (already in use and advocated
by several US and European companies)
and its eventual adoption over the
direct current distribution system.
Three aspects have been conflated into
the “war”: open competition involving
large electric companies and a format
war involving their developing systems,
a general fear in the public’s mind of
death by accidental electrocution from
high voltage AC leading to a debate
over its safety and regulation, and the
debate and behind-the-scene maneuvers
associated with the introduction of the
electric chair.

The wattmeter is an instrument for
measuring the electric power (or the
supply rate of electrical energy) in watts
of any given circuit. Electromagnetic
wattmeters are used for measurement
of utility frequency and audio frequency
power; other types are required for
radio frequency measurements.

Waveguide
(electromagnetism)
In electromagnetics and communications
engineering, the term waveguide may
refer to any linear structure that conveys
electromagnetic waves between its
endpoints. However, the original and
most common meaning is a hollow
metal pipe used to carry radio waves.
This type of waveguide is used as a
transmission line mostly at microwave
frequencies, for such purposes as
connecting microwave transmitters
and receivers to their antennas, in
equipment such as microwave ovens,
radar sets, satellite communications, and
microwave radio links.

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Waveguide
A waveguide is a structure that guides
waves, such as electromagnetic waves or
sound, with minimal loss of energy by
restricting expansion to one dimension
or two. There is a similar effect in water
waves constrained within a canal, or
why guns have barrels that restrict
hot gas expansion to maximize energy
transfer to their bullets. Without the
physical constraint of a waveguide,
wave amplitudes decrease according to
the inverse square law as they expand
into three dimensional space.

Welding
Welding is a fabrication or sculptural
process that joins materials, usually
metals or thermoplastics, by causing
fusion, which is distinct from lower
temperature metal-joining techniques
such as brazing and soldering, which do
not melt the base metal. In addition to
melting the base metal, a filler material
is typically added to the joint to form a
pool of molten material (the weld pool)
that cools to form a joint that is usually
stronger than the base material. Pressure
may also be used in conjunction with
heat, or by itself, to produce a weld.
Welding also requires a form of shield to
protect the filler metals or melted metals
from being contaminated or oxidized.

Whole-life cost
Whole-life cost, or Life-cycle cost (LCC),
refers to the total cost of ownership
over the life of an asset. Also commonly
referred to as “cradle to grave” or
“womb to tomb” costs. Costs considered
include the financial cost which is
relatively simple to calculate and also
the environmental and social costs
which are more difficult to quantify
and assign numerical values. Typical
areas of expenditure which are included
in calculating the whole-life cost include
planning, design, construction and
acquisition, operations, maintenance,
renewal and rehabilitation, depreciation
and cost of finance and replacement or
disposal.

Wiener filter
In signal processing, the Wiener filter
is a filter used to produce an estimate
of a desired or target random process
by linear time-invariant (LTI) filtering
of an observed noisy process, assuming
known stationary signal and noise
spectra, and additive noise. The Wiener
filter minimizes the mean square error
between the estimated random process
and the desired process.

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Wiener process
In mathematics, the Wiener process is
a continuous-time stochastic process
named in honor of Norbert Wiener. It is
often called standard Brownian motion
process or Brownian motion due to its
historical connection with the physical
process known as Brownian movement
or Brownian motion originally observed
by Robert Brown. It is one of the best
known Lévy processes (càdlàg stochastic
processes with stationary independent
increments) and occurs frequently
in pure and applied mathematics,
economics, quantitative finance, and
physics.

Wind farm
A wind farm is a group of wind turbines
in the same location used to produce
electricity. A large wind farm may
consist of several hundred individual
wind turbines and cover an extended
area of hundreds of square miles, but the
land between the turbines may be used
for agricultural or other purposes. A
wind farm can also be located offshore.

Wind power
Williams’s tube

W

The Williams tube, or the Williams–
Kilburn tube after inventors Freddie
Williams (26 June 1911 – 11 August
1977), and Tom Kilburn (11 August 1921
– 17 January 2001), is an early form
of computer memory. It was the first
random-access digital storage device,
and was used successfully in several
early computers.

Wind power is the use of air flow
through wind turbines to mechanically
power generators for electric power.
Wind power, as an alternative to burning
fossil fuels, is plentiful, renewable,
widely distributed, clean, produces
no greenhouse gas emissions during
operation, consumes no water, and
uses little land. The net effects on the
environment are far less problematic
than those of nonrenewable power
sources.

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source of intermittent renewable energy
and are used by many countries as part
of a strategy to reduce their reliance on
fossil fuels.

Wind speed
Wind speed, or wind flow velocity, is
a fundamental atmospheric quantity.
Wind speed is caused by air moving
from high pressure to low pressure,
usually due to changes in temperature.
Note that wind direction is usually
almost parallel to isobars (and not
perpendicular as one might expect),
due to the rotation of the earth.

Wind Turbine
A wind turbine is a device that
converts the wind’s kinetic energy into
electrical energy. Wind turbines are
manufactured in a wide range of vertical
and horizontal axis types. The smallest
turbines are used for applications such
as battery charging for auxiliary power
for boats or caravans or to power traffic
warning signs. Slightly larger turbines
can be used for making contributions
to a domestic power supply while
selling unused power back to the utility
supplier via the electrical grid. Arrays
of large turbines, known as wind farms,
are becoming an increasingly important

Wire
A wire is a single, usually cylindrical,
flexible strand or rod of metal. Wires
are used to bear mechanical loads or
electricity and telecommunications
signals. Wire is commonly formed by
drawing the metal through a hole in a
die or draw plate. Wire gauges come
in various standard sizes, as expressed
in terms of a gauge number. The
term wire is also used more loosely
to refer to a bundle of such strands,
as in “multistranded wire”, which is
more correctly termed a wire rope in
mechanics, or a cable in electricity.

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Wireless Network

Wireless Telegraphy

A wireless network is a computer
network that uses wireless data
connections between network nodes.
Wireless networking is a method by
which homes, telecommunications
networks and business installations
avoid the costly process of introducing
cables into a building, or as a
connection between various equipment
locations. Wireless telecommunications
networks are generally implemented
and administered using radio
communication. This implementation
takes place at the physical level (layer)
of the OSI model network structure.

Wireless telegraphy is the transmission
of electric telegraphy signals without
wires (wirelessly). The term is used
synonymously for radio communication
systems, also called radiotelegraphy,
which transmit telegraph signals by
radio waves. When the term originated
in the late 19th century it also applied
to other types of experimental wireless
telegraph communication technologies,
such as conduction and induction
telegraphy.

Wireless Telephony
Application
A collection of telephony-specific
extensions for call- and feature-control
mechanisms that make advanced mobile
network services available to end users.
WTA essentially merges the features
and services of data networks with the
services of voice networks.

W

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Xx
X-ray
X-rays make up X-radiation, a form of
electromagnetic radiation. Most X-rays
have a wavelength ranging from 0.01
to 10 nanometers, corresponding to
frequencies in the range 30 petahertz
to 30 exahertz (3×1016 Hz to 3×1019 Hz)
and energies in the range 100 eV to 100
keV. X-ray wavelengths are shorter than
those of UV rays and typically longer
than those of gamma rays.

X-ray lithography
A developing technique for production
of very high density structures in
integrated circuits.

XAUI
Innovation of the 10 Gigabit Ethernet
Task Force. XAUI (pronounced “Zowie”)
is a ten Gigabit/second interface. The
“AUI” portion is borrowed from the
Ethernet Attachment Unit Interface. The
“X” represents the Roman numeral for
ten and implies ten gigabits per second.
The XAUI is designed as an interface
extender, and the interface which it
extends is the XGMII, the ten Gigabit
Media Independent Interface.

XCO
Crystal clock oscillator (XCO): An
oscillator that relies on a crystal for
its frequency reference. A piezoelectric
crystal oscillates at a very stable
frequency.

X

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Yy
Yagi Antenna
A Yagi–Uda antenna, commonly known
as a Yagi antenna, is a directional
antenna consisting of multiple parallel
elements in a line, usually half-wave
dipoles made of metal rods. Yagi–Uda
antennas consist of a single driven
element connected to the transmitter
or receiver with a transmission line, and
additional “parasitic elements” which
are not connected to the transmitter or
receiver: a so-called reflector and one
or more directors.

Y/C
Y, C, YUV, Y-Pb-Pr, YCbCr, and Y/C
(also known as S-video) are terms that
refer to video signal components. The
black and white (luminance) portion of
the video signal is the “Y” component
which, when combined with color
components, form a complete picture.
The different nomenclatures for the
color components reflect different color
encoding schemes.

YIG
Yttrium-iron-garnet (YIG) is a
ferrimagnetic material used for solidstate lasers and for microwave and
optical communications devices.

Y-delta transform
The Y-Δ transform, also written wyedelta and also known by many other
names, is a mathematical technique to
simplify the analysis of an electrical
network. The name derives from the
shapes of the circuit diagrams, which
look respectively like the letter Y and
the Greek capital letter Δ. This circuit
transformation theory was published by
Arthur Edwin Kennelly in 1899.

Y

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Zz
Z3 (computer)
The Z3 was an electromechanical
computer designed by Konrad Zuse.
It was the world’s first working
programmable, fully automatic digital
computer. The Z3 was built with 2,000
relays, implementing a 22-bit word
length that operated at a clock frequency
of about 5–10 Hz. Program code and
constant data were stored on punched
film. The Z3 was completed in Berlin
in 1941. The German Aircraft Research
Institute used it to perform statistical
analyses of wing flutter.

z80
The Z80 CPU is an 8-bit based
microprocessor. It was introduced by
Zilog in 1976 as the startup company’s
first product. The Z80 was conceived
by Federico Faggin in late 1974 and
developed by him and his then-11
employees at Zilog from early 1975
until March 1976, when the first fully
working samples were delivered. With
the revenue from the Z80, the company
built its own chip factories and grew
to over a thousand employees over the
following two years

Z-Axis
In a gyro, an axis through the center of
gravity and mutually perpendicular to
both the X (spin) and Y axes.

Zener diode
A Zener diode is a particular type of
diode that, unlike a normal one, allows
current to flow not only from its anode
to its cathode, but also in the reverse
direction, when the Zener voltage is
reached.

Zigzag transformer
A zigzag transformer is a specialpurpose transformer with a zigzag
or “interconnected star ” winding
connection, such that each output is
the vector sum of two (2) phases offset
by 120°. It is used as a grounding
transformer, creating a missing neutral
connection from an ungrounded 3-phase
system to permit the grounding of that
neutral to an earth reference point; to
perform harmonic mitigation, as they
can suppress triplet (3rd, 9th, 15th,
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21st, etc.) harmonic currents; to supply
3-phase power as an autotransformer
(serving as the primary and secondary
with no isolated circuits); and to supply
non-standard, phase-shifted, 3-phase
power

Zener Effect
A reverse breakdown effect in diodes
in which breakdown occurs at reverse
voltages below 5 volts. The presence of
a high energy field at the junction of a
semiconductor produces the breakdown.

Zener Voltage
The break-down voltage of a zener
diode.

Zilog
Zilog, Inc. is an American manufacturer
of 8-bit and 16-bit microcontrollers.
Its most famous product is the Z80
series, 8-bit microprocessors that were
compatible with the Intel 8080 but
cheaper. The Z80 was widely used
during the 1980s in many popular
home computers such as the TRS-80
and the ZX81. The company also made
16- and 32-bit processors, but these
did not see widespread use. From the
1990s the company focused primarily
on the microcontroller market. The
name (pronounced with a long “i”) is
an acronym of Z integrated logic, also
thought of as “Z for the last word of
Integrated Logic”.

Zero Adjustment
Zero adjustment refers to the output
value when the input is at 0%, its lowest
possible range value (LRV). For example,
in a 4-20 mA system, the output is 4 mA
when the input value is at 0%.

Zero-bit Insertion
Z

A transmission process when additional
zeros are inserted after a fixed number of
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Zip-Cord

ones in a transmission sequence to ensure
that data will not be misinterpreted as
controlling information.

A two-fiber cable consisting essentially
of two single-fiber cables having their
jackets conjoined by a strip of jacket
material, so that they may be easily
furcated [divided] by slitting or tearing
the two jackets apart, permitting the
installation of optical connectors.

Zerofill
To fill unused storage locations with the
representation of the character denoting
0 [memory]. To insert zeros into a data
stream [protocol].

Zeroing
The process of adjusting a synchro or
some other component to its electrical
zero position.

Zero Insertion Force
A class of IC sockets which clamp the IC
pins (via a small lever on the side of the
socket) after insertion, and thus require
no downward force on the IC or its pins
to insert it into the socket. Especially
useful in applications in which repeated
insertions subjects the IC or the socket
to wear and breakage.

ZIP Drive
A floppy drive system developed by
Iomega which had a much larger storage
capacity than normal floppy disk drives.
This style drive was widely used, along
with floppy drives, before the advent
of larger memory USB thumb drives.

ZIGBEE
A standard for short-distance, lowdata-rate communications using the
frequencies and physical and data layers
of the IEEE 802.15.4 PHY specification.
Created and maintained by the ZIGBEE
Alliance Group.

Z
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Zone of Mutual Visibility
The area where the satellite can be seen
by both the up- and down-link earth
terminals.

Zone of Silence
Skip zone. The region between alternate
reflections of a radio wave, in which no
signal is detectable.

Zone Plate
A flat glass plate with concentric opaque
rings that forms an image caused by
diffraction rather than reflection.

Z-transform
In mathematics and signal processing,
the Z-transform converts a discretetime signal, which is a sequence of real
or complex numbers, into a complex
frequency domain representation. It
can be considered as a discrete-time
equivalent of the Laplace transform.
This similarity is explored in the theory
of time scale calculus.

Zulu Time
Z-parameters
Impedance parameters or Z-parameters
are properties used in electrical
engineering, electronic engineering, and
communication systems engineering to
describe the electrical behavior of linear
electrical networks. They are also used
to describe the small-signal response of
non-linear networks.

Zulu Time is used to refer to the current
time in Greenwich, England. To avoid
confusion about time zones and daylight
saving time, a Global Time was created.
This Global time has many names. It
used to be called GMT. Now its called
UTC, Zulu Time or Z Time!

Z
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container orchestration systems such as
Kubernetes and Docker Swarm. When
a Kubernetes Deployment is scaled to
zero replicas, its Pod will be deleted.

ZVC
Zero crossing (or burst-firing) control
is an approach for electrical control
circuits that starts operation with the
AC load voltage at close to 0 volts in
the AC cycle. This is in relation to solid
state relays, such as triacs and silicon
controlled rectifiers

ZS
Zero scale as the idea that a function can
be reduced down to zero replicas when
idle and brought back to the required
amount of replicas when it is needed.
The building block for this exists in most

ZVS
Zero Voltage Switching means that the
power to the load (heater or cooler or
other device) is switched on or off only
when the output voltage is zero volts.

Z
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