|
A/D Converter
|
Analogue to digital.
Specifically: A/D converter, a circuit that converts analogue signals into a
stream of digital data.
|
|
AC
|
Alternating
current: A signal or power source that varies with time, switching
polarities. Typically, sinusodial and at constant
frequency.
|
|
ACB
|
Air Circuit
Breaker. The term is usually applied only to the larger type of current
breaking device, where the high energy required to move
heavy contacts quickly is stored in a spring, and manual operation of the
mechanism is by pushbutton, or automatic electrical control. An ACB may have
only a switching function, or may include an automatic tripping function in
the event of a high current.
|
|
Ah
|
Ampere-hour(s): A measure of battery capacity. A 4Ah battery could, for instance, deliver 1A
for 4 hours, 1/2A for 8 hours, etc.
|
|
AIS
|
Alarm indication system.
|
|
Ampere
|
Ampere(s), the
unit of electrical current. Current is defined as the amount of charge that
flows past a give point, per unit of time.
The symbol I is used for current in equations
and A is the abbreviation for ampere.
|
|
Analogue
|
A system in which values are given as
infinitely variable quantities, even though the value is expressed in units,
i.e. 2 1/3 By contrast, a digital system handles a
signal as a stream of numbers, and accuracy is dependant on the smallest
increment used.
|
|
AND
|
Combining two
signals so that the output is on only if both signals are present. This can
be accomplished by an AND logic gate (two inputs, one output which is high if
both inputs are).
|
|
ATS
|
An Automatic Transfer Switch. The output of this
item is sourced from one of two power inputs, (basically a two-way switch
with the “common” as the output). If the two sources are defined as “normal”
and “standby”, then when both of these are live, the device will connect to
the “normal”. If the normal supply is
lost, but the standby is live, the device will change over to use that
supply. Most types also close volt-free contacts when the normal supply is
lost, and this is used to start generators. When the normal supply returns, then the device will re-connect to it
only when both supplies are in phase, to avoid tripping of protective devices
downstream. ASCO is a major manufacturer of these devices.
|
|
Autotransformer
|
An autotransformer is a transformer that uses a common winding for both the primary and
secondary windings. Essentially an inductor with a centre-tap, an
autotransformer is often used in power-supply boost-converter applications to
achieve a higher output voltage, while limiting the peak fly-back voltage
seen by the power switch.
|
| Backup Step-Up |
Step-up, switching-regulator power supply with a backup battery switchover.
|
|
Battery Backup
|
A feature of microprocessor-supervisory circuits and some power supplies to switch between
a main power source and a battery.
|
|
Battery Monitor
|
A feature that monitors the voltage on a battery and indicates when the battery is low. It
is usually implemented using a comparator to compare the battery voltage to a
specified level.
|
|
Battery Switchover
|
A circuit that switches between the higher of a main supply and a backup battery.
|
|
BCD
|
Binary-coded decimal: Representation of a number in which each decimal digit (0-9) is
encoded in binary, with four bits per decimal digit.
|
|
Blade Server
|
A blade server is a computer on a motherboard, which includes processor, memory, and sometimes storage. The blade server is intended to address the needs of large-scale computing centres to reduce space requirements and lower costs."
|
|
BMS
|
Building Management System. An electronic
control system used for the many automatic functions required in a modern
building.
|
|
Boost Converter
|
A power supply that steps an input voltage up (boosts it) to a higher, regulated voltage.
|
|
Break-Before-Make
|
A switch that is configured to break (open) the first set of contacts before
engaging (closing) the new contacts. This prevents the momentary connection
of the old and new signal paths. Applies to mechanical systems (e.g. that
use relays or manual switches) and to solid-state analogue multiplexers and
switches.
|
|
Bridge Battery
|
A battery intended to provide power to system memory while the main battery is
replaced.
|
|
Brownout
|
A condition where the voltage supplied to the system falls below the specified operating
range, but above 0V.
|
|
Business Continuity
|
Term used for all concerns with failure
of IT equipment, or the ability to employ it effectively. Items affecting
Business Continuity range from loss of power, to floods, terrorist attacks,
or anything that causes loss of business.
|
|
Business Critical
|
This is used to identify those factors most affecting business if a problem occurs.
Usually applied to vital power supplies.
|
|
CAD
|
Computer-aided design
|
|
Castell lock
|
Where it is necessary to ensure that only one or neither ACB of a pair can close, a key
system can be fitted. This can control many ACBs, inhibiting pre-determined
combinations of closures.
|
|
CC/CV Charger
|
Constant Current/Constant Voltage battery charger
|
|
CCCv
|
Constant current/constant voltage
|
|
Charge Pump
|
A power supply which uses capacitors to store and transfer energy to the output, often
stepping the voltage up or down. Charge is transferred from one capacitor to
another under control of regulator and switching circuitry.
|
|
Current-Sense Amplifier
|
An amplifier that measures current by measuring the voltage drop across a resistor placed
in the current path. The current sense amp outputs either a voltage or a
current that is proportional to the current through the measured path.
|
|
D/A Converter
|
Digital-to-analogue converter (DAC): A data converter, or DAC, that receives digital data (a
stream of numbers) and outputs a voltage or current proportional to the value
of the digital data.
|
|
Daisy Chain
|
A method of propagating signals along a bus in which the devices are connected in series
and the signal passed from one device to the next. The daisy chain scheme
permits assignment of device priorities based on the electrical position of
the device on the bus.
|
|
Data Acquisition System
|
System which acquires data, generally by digitizing analogue channels and storing the data
in digital form. These systems can be standalone or married to a computer and
can acquire multiple channels of data.
|
|
Data Converter
|
A/D or D/A converter: An electronic circuit that converts analogue signals to digital,
or vice-versa. An analogue signal is a continuously varying voltage or
current. Its digital counterpart is a stream of digital numbers, each
representing the amplitude of the analogue signal at a moment in time.
|
|
DC
|
Direct current
|
|
DC-DC Controllers
|
A DC-DC converter (switch-mode power supply) in which the power switch (usually a
power MOSFET) is external to the IC.<
|
|
DIO
|
Data input/output
|
|
DMM
|
Digital Multimeter: Measuring instrument or VOM (e.g. voltage,
resistance, current) with a digital display.
|
|
DPDT
|
Double-pole double throw
|
|
DPST
|
Double-pole single throw
|
|
DVM
|
Digital Voltmeter
|
|
Electrical interlock
|
Where it is necessary to ensure that only one or neither ACB of a pair can close, but
never both together, this can be assured with an electrical circuit using
shunt trips or undervoltage releases in both ACBs, each operated by contacts
in the other. If both ACBs use an undervoltage release for this purpose, then loss of
the control circuit power will cause both ACBs to open, without any means of
closing by hand. This particular method is therefore highly unsuitable for
buildings with critical power requirements.
|
|
EPROM
|
Erasable programmable read-only memory
|
|
Essential Supplies
|
In an electrical context, those supplies
that power items required for Health and Safety (extract fans, fire pumps
etc.) and vital IT equipment.
|
|
ESR
|
Effective Series Resistance (or Equivalent Series Resistance or ESR) is the resistive
component of a capacitor's equivalent circuit. A capacitor can be modelled as an ideal
capacitor in series with a resistor and an inductor. The resistor's value is
the ESR.
|
|
F
|
Farad(s): Unit of capacitance
|
|
Fail-Safe
|
If a malfunction occurs, equipment reverts to safe condition. In power supply
equipment, this usually means all “off”.
|
|
Fault tolerant
|
A characteristic of a system that ensures it will still function correctly even
after a fault occurs that would cause a normal circuit to malfunction.
|
|
Harmonic Distortion
|
The presence of frequencies in a power supply that cause a distortion from a pure
sine-wave. In buildings where multiple computers are in use, these
distortions are caused mainly by the rectifiers within the computer’s power
supply unit, which take current mostly around the peak of the voltage
waveform. This causes a large “third” harmonic, which in turn can cause
unacceptably large neutral currents in a three phase system. Further distortion is added by the use of
fluorescent lighting.
|
|
HD
|
See Harmonic distortion
|
|
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. Hot-swap devices typically
protect against, undervoltage, and
inrush current that can cause faults, errors, and hardware damage.
|
|
Hz
|
Hertz: A measure of frequency. An older term is cycles per second, or cps.
|
|
I/O
|
Input/output
|
|
IC
|
1. Integrated circuit: A semiconductor device that combines multiple transistors and other
components and interconnects on a single piece of semiconductor material.
2. Internally Connected
|
|
IEC
|
Integrated electronic component
|
|
Inductive Kickback
|
The very rapid change in voltage across an inductor when current flow is interrupted. Snubber diodes are often used to channel
this energy in relays, and other inductive loads. Kickback can be a problem (causing EMI and
component failure); or it can be used in power supply circuits to develop
higher or opposite-polarity voltages from a single supply.
|
|
Inrush Current
|
A momentary input current surge, measured during the initial turn-on of the power supply.
This current reduces to a lower steady-state current once the input
capacitors charge. Hot-swap controllers or other forms of protection are
often used to limit inrush current, because uncontrolled inrush can damage
components, lower the available supply voltage to other circuits, and cause
system errors.
|
|
Inverting Switching Regulator
|
A switch-mode voltage regulator in which output voltage is negative with respect to its
input voltage.
|
|
ISO
|
International Standards Organization
|
|
J
|
Joule(s)
|
|
k
|
1. Kilo: Metric
unit representing 1000. E.g.: 1 kHz is a 1 kilohertz (1000 Hertz). Note that
the k is always lowercase.
2. Kelvin: Temperature scale. Zero K is
defined as absolute zero. 273.15 K is 0 degrees C.
Note that temperatures on the scale are called kelvins, not "degrees kelvin." The K symbol is
uppercase and used without a degree symbol. The word kelvin" in this context is not capitalized.
|
|
K
|
Kelvin
|
|
kHz
|
Kilohertz
|
|
km
|
Kilometre(s)
|
|
kVA
|
Kilovolt(s)-ampere(s)
|
|
kW
|
Kilowatt(s)
|
|
kWh
|
Kilowatt hour(s)
|
|
LAN
|
Local Area Network: A computer network, usually within one building, that connects
computers, file and mail servers, storage, peripherals, and other devices in
a way that permits data interchange and sharing of resources. Ethernet and (802.11) are common examples.
|
|
LCD
|
Liquid-crystal display
|
|
Leakage Inductance
|
An inductive component present in a transformer that results from the imperfect magnetic
linking of one winding to another.
|
|
LED
|
Light-Emitting Diode: A semiconductor device that emits light (usually visible or infrared)
when forward-biased.
|
|
Line Regulation
|
The ability of
a power-supply voltage regulator to maintain its output voltage despite
variations in its input voltage.
|
|
Linear
|
1. Having the property that the output is proportional to the input. E.g.: V out=k*V in where k is a constant.
2. Analogue; as in a "linear" circuit (as opposed to digital).
|
|
Linear Regulator
|
A voltage regulator that is placed between a supply and the load and provides a
constant voltage by varying its effective resistance.
|
|
Lithium batteries
|
Lithium batteries for low-power, high-reliability, long-life applications such as
non-volatile memory and timekeeping (typically in coin-shaped cells) use a
variety of lithium-based chemistries (as differentiated from lithium-ion).
|
|
Lithium-ion batteries
|
Lithium and lithium-ion: A number of battery chemistries are based on the element
lithium, a highly-reactive metallic element. Lithium-based batteries are
common in two applications: Power for portable equipment such as cell phones,
laptops, and MP3 players; and low-power, long-life applications such as
powering memory elements and clocks.
|
|
LOP
|
Loss of power
|
|
LOS
|
Loss of signal
|
|
Low Batt Det
|
Low battery detector
|
|
M2M
|
Machine-to-machine or machine-to-mobile communications, via wireless technologies such as cell
phone network technologies, WLAN, Bluetooth, and RFID (radio frequency
identification). Applications include automatic meter reading, fleet
management, vending, monitoring and control, security and alarms, and
telemedicine.
|
| mA |
Milliampere or milliamp: 1/1000 of an Ampere. Ampere is the basic unit for measuring electrical current.
|
| mAh |
Milliamphours
|
|
MAXTON
|
Maximum time-on
|
|
MBB
|
Make-before-break: In a switching device, a configuration in which the new connection path is
established before the previous contacts are opened. This prevents the
switched path from ever seeing an open circuit. Applies to mechanical systems (e.g. that
use relays or manual switches) and to solid-state analog multiplexers and switches.
|
| Mcps |
1. Megacycles per second (obsolete): now Megahertz
2. Megachips per Second: In a Direct-Sequence Spread
Spectrum signal, a "chip" is an encoding element. Mcps is a measure of the speed at which chips can be
generated by a circuit.
|
|
MHz
|
Megahertz (MHz): Measurement of frequency -- million cycles per second.
|
|
MTBF
|
Mean Time Between Failures. A highly theoretical calculated value of time, used to
evaluate probability of failure of a complete system, and in some cases to
plan maintenance regimes.
|
|
Multiplex
|
1. Combining two signals (which can be analogue or a digital stream) into one in such a
way that they can later be separated. Examples are OFDM; standard FM stereo
broadcast (in which left and right are multiplexed onto one base-band
signal); standard television in which video and several audio signals shared
the channel; and time-division multiplexing which gives each signal a
separate time-slice.
2. An array of analogue switches, usually on a single CMOS chip, that allows one input
signal to be routed to any of several output lines, depending on the value of
a set of digital control lines. A multiplexer can also be used in the
opposite direction, allowing the array to connect one of several input lines
to the output, depending on the control lines. Several of these can be implemented on
one chip to make a multi-channel version.
|
|
Murphy's Law
|
"Anything that can go wrong, will go wrong."
|
|
mV
|
Megavolt(s)
|
| mW |
Milliwatt
|
|
MW
|
Megawatt(s)
|
| nA |
Nanoampere(s)
|
|
Nanovolt
|
Nanovolt (nV): Unit of measure. A billionth of a volt.
|
|
NC
|
Normally closed (switch contacts)
|
| NiMH |
Nickel metal hydride: A rechargeable-battery technology.
|
| NO |
Normally open (Switch contact)
|
|
Nonvolatile
|
Nonvolatile (NV) RAM is memory which retains its stored value when power is removed.
|
|
ns
|
Nanosecond(s)
|
|
NV-S
|
Nanovolt seconds
|
|
nW
|
Nanowatt
|
|
OC
|
Overcurrent
|
|
OC-48
|
A fibre-optic line capable of 2400 megabits per second.
|
| OEM |
Original equipment manufacturer
|
|
OLT
|
Optical line transmission
|
|
OR
|
Combining two signals so that the output is on if either signal is present. This can be
accomplished by an OR logic gate (two inputs, one output which is high if
either input is). It can also be done with a
"wired-OR" connection in which two signals are simply wired
together and either one of them can raise the level. This works when the
signals are driven by a source that only pulls up or only pulls down, with a
resistive load (e.g. an "open collector" output).
|
|
P-P
|
Peak-to-peak
|
|
PLC
|
An electronic device that receives input signals, in on/off (high/low) or analogue form,
and operates output contacts according to a pre-written programme for each
and all possible input states/combinations.
|
|
PFR
|
Phase Failure Relay. A device that monitors an
electrical supply (usually a mains 3 phase supply), so that if the supply
fails, contact within the device are operated, to initiate automatic remedial
action, such as starting of generators and changing of load to this source.
These devices are usually designed to operate if either frequency, phase sequence, or voltage are outside pre-determined
values.
|
|
Potentiometer
|
Variable resistor in which a wiper sweeps from one end of the resistive element to the
other, resulting in resistance that is proportional to the wiper's position.
|
|
PCB
|
A printed circuit board, or PC board, or PDB, is a non-conductive material with
conductive lines printed or etched. Electronic components are mounted on the
board and the conductive “lands” connect the components together to form a
working circuit or assembly.
|
|
PROFIBUS
|
Vendor-independent open fieldbusstandard used in manufacturing,
building automation, and process control. Utilizes a nonpowered two-wire (RS-485) network. PROFIBUS is standardized under
the European Fieldbus Standard EN 50 170. It includes three versions:
FMS, DP, and PA. Visit www.profibus.com for more information.
|
|
PROM
|
Programmable read-only memory
|
|
PRT
|
Platinum Resistance Thermometer, a resistance temperature device (RTD).
|
|
RAM
|
Random access memory
|
|
RC
|
Resistance-capacitance; resistor-capacitor
|
|
Ready to close contact.
|
If an ACB is fitted with multiple release coils, such as shunt trips and/or undervoltage
releases, a “lock up” situation can occur if coils requiring open and close
functions are operated at the same time, (the ACB will stay open), and then
the open command is relinquished; the ACB will not close unless the remaining
close signal is removed and then reinstated. Insertion of a ready-to-close
contact in series with the close signal, isolates commencement of closure until the device is no longer
held open by any other
factor.
|
|
RH
|
Relative humidity
|
|
ROM
|
Read-only memory
|
|
RTCs
|
Real-time clock: Integrated circuit that contains a timer that supplies the time of day
(and often, the date). An RTC generally contains a long-life battery to allow
it to keep track of the time even when there is no power applied.
|
|
SPC
|
1. Samples per second. In data conversion, an analogue signal is converted to a stream of numbers, each
representing the analogue signal's amplitude at a moment in time. Each number
is called a "sample." The number sample per second is called the
sampling rate, measured in samples per second.
Also;
2. ksps: Kilosample(s) per second (thousands of samples per second)
3. Msps: Megasamples per second (millions of samples per second)
|
|
Sampling Rate
|
An A/D converter converts an analogue
signal into a stream of digital numbers, each representing the analogue
signal's amplitude at a moment in time. Each number is called a
"sample." The number sample per second is called the sampling rate,
measured in samples per second.
|
|
SCR
|
Silicon-controlled rectifier. A semiconducting device that acts as a
switch; When a voltage is applied, no current flows unless a small current is
made to flow into the “gate” connection, which causes to main device to
conduct, with a volt drop of approx. 1V. The device will continue to conduct,
even without the gate signal, until the main current is made to cease. The
device will then revert to the non-conducting state until another “gate”
current is inserted.
|
|
Second Harmonic Distortion
|
Second harmonic distortion (HD2): Ratio of second-order harmonic to the input signal
(carrier). Often measured as dBc.
|
|
Shift Register
|
Two or more bi-stable elements (flip-flops) connected in series. With each tick of the clock, the
output of stage n is shifted to stage n+1. Applications include clock or
signal delays, delay lines, linear-feedback shift registers.
|
|
Shunt release
|
See Shunt trip.
|
|
Shunt trip
|
A solenoid coil in an ACB, which when energised is used to operate it to the “off”
position and/or ensure that it cannot be closed. Only when the coil is not
energised can the ACB be closed.
|
|
Signal Conditioner
|
A device placed between a signal source and a readout instrument to change the signal.
Examples are attenuators, preamplifiers, charge amplifiers, and sophisticated
level-translating devices that can compensate for
non-linearities in the sensor or amplifier.
|
|
Smart Battery
|
A battery with internal circuitry that provides level of charge status to the host system.
|
|
SMPS
|
Switch-Mode Power Supply
|
| Snubber |
A device which suppresses voltage transients.
|
|
Soft Start
|
A feature in some switching power supplies that limits the inrush current at initial start-up.
|
|
SPDT
|
Single-pole/double-throw switch
|
|
SPOF
|
Single point of failure. A part of the system that, if failed, causes malfunction of the system as a whole.
|
|
SPST
|
Single-pole/single-throw switch
|
|
SRAM
|
Static RAM: RAM that does not require a clock to retain its contents.
|
|
Switch Mode
|
Uses a switching transistor and inductor to control/regulate the charging voltage/current.
|
|
Switching Regulator
|
A voltage regulator that uses a switching element to transform the supply into an
alternating current, which is then converted to a different voltage using
capacitors, inductors, and other elements, then converted back to DC. The
circuit includes regulation and filtering components to insure a steady
output.
|
|
Synchronous Rectification
|
In switch-mode power supplies, the "steering" diode is replaced or paralleled with
a FET switch to reduce losses and thereby increase efficiency. The FET is off
during the inductor charge cycle, and then turned on as the inductor
discharges into the load.
|
|
Thermal Control Circuit
|
Circuit to monitor and control the temperature of something. For example the integrated
temperature controller in Intel's processors.
|
|
Thermal Shutdown
|
Deactivating a circuit when a measured temperature is beyond a predetermined value.
|
|
Thermistor
|
A temperature-dependent resistor with a high temperature coefficient, usually composed of sintered semiconductor material.
|
|
Thermocouple
|
A temperature sensor formed by the junction of two dissimilar metals. A thermocouple
produces a voltage proportional to the difference in temperature between the
hot junction and the lead wire (cold) junction.
|
|
Thermostat
|
Circuit that indicates whether a measured temperature is above or below a particular
temperature threshold or trip point. Used for thermal protection and simple
temperature control systems.
|
|
Transistor
|
A basic solid-state control device which allows or disallows current flow between two
terminals, based on the voltage or current delivered to a third terminal.
|
|
Triple Redundancy
|
A term used to indicate that three systems are used, such that if two fail, operation is
still possible. This applies only
to manually controlled systems, because with an automatic system, there is no
means of identifying which parts are correctly functioning and which are not.
|
|
Triplex
|
A term used to the most extent in the Civil Aircraft Industry, usually for “blind” landing
systems, (first in 1962). By using three identical control circuits, each with separate inputs, any fault
that may arise will cause one circuit only to operate in a different manner
from the other two. By acting only on information from the two
circuits remaining in agreement, a single fault can be tolerated, and without
causing any malfunction of the system overall. It is essential however to
automatically diagnose this condition and make it known.
|
| Triplicated System |
A term used where three identical systems are used in an attempt to gain reliability. For
automatic electrical systems, it is essential to include a means of
identifying which of the three circuits is not in agreement with the
other two, and arrange that this system is overruled by the two correct
systems. If this is achieved, the system is in triplex form.
|
|
Undervoltage coil
|
A solenoid coil in an ACB, which when de-energised is used to operate it to the “off”
position and/or ensure that it cannot be closed. Only when the coil is
energised can the ACB be closed
|
| Undervoltage release |
See Undervoltage coil |
| U.P.S. |
Uninterruptible power supply. Battery powered unit, that converts power from
the batteries to useable AC power, in order to temporarily replace normal
power when lost.
|
|
UVLO
|
Undervoltage lockout
|
|
V-s
|
Volt-second(s)
|
|
V/F
|
Voltage-to-frequency
|
|
VA
|
Volt ampere(s)
|
|
Volt
|
Volt (or Volts): Unit of measure for electromotive force (EMF), the electrical
potential between two points. An electrical potential of 1 volt will push 1
ampere of current through a 1-ohm resistive load.
|
|
Volt free contact
|
A pair of contacts that are neither
connected to any other point or earth, and can therefore be used in any
circuit.
|
|
Voltage Regulator
|
A circuit which is connected between the power source and a load, which provides a
constant voltage despite variations in input voltage or output load.
|
|
VOM
|
Volt-Ohm meter
|
|
VP-P
|
Peak-to-peak voltage
|
|
W
|
Watt(s)
|
|
Watchdog
|
A feature of a
microprocessor-supervisory circuit that monitors software execution in a
microprocessor or microcontroller.
|
|
ZVS
|
Zero voltage switching.
|
