Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

arrester discharge voltage
the voltage in an arrester during a surge.
artificial dielectric
a dielectric material that has been modified to alter its properties. Common modifications include micro-machining to remove material from the substrate under planar patch antenna to improve radiation properties and the fabrication of periodic arrays of holes to realize guiding or photonic bandgap structures.
artificial intelligence
the study of computer techniques that emulate aspects of human intelligence, such as speech recognition, logical inference, and ability to reason from partial information.
ASCII
American standard code for information interchange.
aspect ratio
(1) the size invariant ratio of length to width for a rectangular box enclosing a shape, the orientation of the box being chosen to maximize the ratio. This measure is used to characterize object shapes as a preliminary to, or as a quick procedure for, object recognition.
(2) the ratio of width to height for an image or display.
(3) in television or motion pictures, the algebraic ratio of picture width to height. At present, the television format in the United States consists of a width to height ratio of 4 to 3.
asymmetric digital subscriber line (ADSL)
a digital subscriber line (DSL) in which the rate from central switching office (CO) to customer premise is much faster than the rate from customer premise to CO.
asynchronous
not synchronous.
asynchronous AC systems
AC systems either with different operating frequencies or that are not in synchronism.
asynchronous bus
a bus in which the timing of bus transactions is achieved with two basic "handshaking" signals, a request
signal from the source to the destination and an acknowledge signal from the destination to the source. The transaction begins with the request to the destination. The acknowledge signal is generated when the destination is ready to accept the transaction. Avoids the necessity to know system delays in advance and allows different timing for different transactions.

See synchronous bus
asynchronous circuit
(1) a sequential logic circuit without a system clock.
(2) a circuit implementing an asynchronous system. asynchronous demodulation a technique for extracting the information-carrying waveform from a modulated signal without requiring a phase-synchronized carrier for demodulation.
See synchronous demodulation
asynchronous machine

See induction machine
asynchronous operation
a term to indicate that a circuit can operate or a communication system can transmit information when ready without having to wait for a synchronizing clock pulse.
asynchronous system
a (computer, circuit, device) system in which events are not executed in a regular time relationship, that is, they are timing-independent. Each event or operation is performed upon receipt of a signal generated by the completion of a previous event or operation, or upon availability of the system resources required by the event or operation.
asynchronous transfer mode (ATM)
method of multiplexing messages onto a channel in which channel time is divided into small, fixed-length slots or cells. In ATM systems the binding of messages to slots is done dynamically, allowing dynamic bandwidth allocation. ATM is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic.
atmospheric attenuation
decrease in the amplitude of a signal propagating through the atmosphere, due primarily to absorption and scatter.
attenuation constant
the real part of the complex propagation constant for an electromagnetic wave.
automatic
(1) property pertaining to a process or a device that functions without intervention by a human operator under specified conditions.
(2) a spring-loaded tension sleeve into which a conductor or other wire is inserted for tensioning and attachment to a pole or other fixture.
automatic circuit recloser

See recloser
automatic frequency control (AFC)
(1) an automatic feedback control system that is used to maintain active power balance by means of the speed governor system. In an interconnected system, scheduled power interchanges are maintained by means of controlling area generations.
(2) electronic circuitry used to keep the received signal properly placed within the desired IF frequency range. In televisions, the AFC circuitry is also called the AFT or "automatic fine tuning" section. The AFC circuit will generate an error signal if the input frequency to the IF drifts above or below the IF frequency. The error signal is fed back to vary the local oscillator frequency in the tuner section. See also automatic fine tuning (AFT).
automatic gain control (AGC)
a method to control the power of the received signal in order to be able to use the full dynamic range of the receiver and to prevent receiver saturation.
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