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Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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.
askarel
a trade name for an insulating oil.

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.
ATM
See asynchronous transfer mode
atmosphere
a convenient measure of pressure. 1 std atm = 14.696 psia (pounds per square inch absolute).

atmospheric attenuation
decrease in the amplitude of a signal propagating through the atmosphere, due primarily to absorption and scatter.

atom
a particle of matter indivisible by chemical means, which is chemically neutral. It is the fundamental building block of the chemical elements.
attenuation
the exponential decrease with distance, in the amplitude of an electric signal traveling along a very long transmission line due to losses in the supporting medium. In electromagnetic systems attenuation is due to conductor and dielectric losses. In fiber optic systems attenuation arises from intrinsic material properties (absorption and Rayleigh scattering) and from waveguide properties such as bending, microbending, splices, and connectors.
attenuation constant
the real part of the complex propagation constant for an electromagnetic wave.

attenuator
a device or network that absorbs part of a signal while passing the remainder with minimal distortion.