Electronic Engineering Dictionary

Aperature Time. The time it takes for a switch to turn from ON to OFF.

Aperiodic. A non-repetitive signal, which occurs at irregular intervals.

Apparent Drift. The effect of the earths rotation on a gyro that causes the spinning axis to appear to make one complete rotation in one day.

Apparent Power. That power apparently available for use in an ac circuit containing a reactive element. It is the product of effective voltage times effective current expressed in volt-amperes. It must be multiplied by the power factor to obtain true power available. In alternating-current power transmission and distribution, the product of the rms voltage and amperage.

Arbiter. A functional module that accepts bus requests from requester modules and grants control of a data bus to one requester at a time.

Arbitration. The process of selecting one communication node on a bus over another. The process of giving control of an interface bus to a requester of the data bus.

Arc. A visible electrical discharge between separated contacts.

Arc Fault Circuit Interrupter. [AFCI] An AFCI acts like a circuit breaker, interrupting the circuit when a high energy arc is detected. Low energy arcs which are common when changing a switch position or plugging in a device are ignored. Because an AFCI device is designed to detect an arc, the arc must occur first, so an AFCI will never interrupt a circuit until after the first arc. An AFCI may also be combined with a GFCI for ground fault protection, or a circuit breaker for overload and short-circuit protection. An AFCI outlet may have a test switch just as a GFCI outlet.

Arcing. A luminous electrical discharge (bright, electrical sparking) through the air that occurs when high voltages exist across a gap between conductors.

Arc-over Voltage. The minimum voltage required to cause an arc between electrodes separated by a gas or liquid insulation.

Architecture. Defines how a system is connected or interconnected and in some cases how the components are interconnected.

Areal Density. The Bit density of the data stored on the media of a hard disk drive.

Armature. The movable element in an electro-mechanical device. In a relay, the movable portion of the relay. The windings in which the output voltage is generated in a generator or in which input current creates a magnetic field that interacts with the main field in a motor.

Armature Losses. Copper losses, eddy current losses, and hysteresis losses that act to decrease the efficiency of armatures.

Armature Reaction. The effect in a dc generator of current in the armature creating a magnetic field that distorts the main field and causes a shift in the neutral plane.

Armature Rotor. The rotor is the part or the motor that spins. The armature rotor is wire wound and has a laminated core similar to that of the squirrel cage rotor.

Armor. A flexible metal 'shield' that protects a component from damage. Refer to Cable Armor definition. A component intended to protect the critical internal components, e.g., buffer tubes or fibers, or electrical conductors, from damage from external mechanical attack [rodent attack or abrasion].

Armored Cable. A cable provided with a wrapping of metal, usually steel wires or aluminum tape, primarily for the purpose of mechanical protection.

Armstrong Oscillator. A type of oscillator. The Armstrong Oscillator is used to produce a sine-wave output of constant amplitude and of fairly constant frequency within the rf range. Read more on Armstrong Oscillators, or Crystal Controlled Armstrong Oscillators. Also refer to a list of Oscillator Vendors.

Array. A group of devices or components. A number of devices contained within a single package, but not connected to each other. Also see Transistor Arrays. Types of Diode Arrays, or Resistor Arrays. The side-bar Graphic shows a transistor array in an LCC package. Also see Antenna Array [within the Antenna Dictionary].

Arrester. Surge Arrester, or Lightning Arrester. Lightning arresters are devices for protecting many different pieces of equipment such as, power poles and towers, power transformers, and circuit breakers from damage from lightning strikes. A device that protects hardware, such as systems, subsystems, circuits, and equipment, from voltage or current surges produced by lightning or electromagnetic pulses.

Artificial Transmission Line. An LC network that is designed to simulate characteristics of a transmission line.

ASCII. The American Standard Code for Information Interchange. A common method used by computers to code alphabetic letters into a binary code. Refer to table of ASCII Codes.

Aspect Ratio. The ratio between the width of an object and the height of the object. The 4:3 aspect ratio of a traditional TV or monitor or the 16:9 aspect ration for newer monitors.

Assembly. A number of parts or sub-assemblies, or any combination thereof, joined together to perform a specific function. As in a Printed Wiring Board Assembly, which comprises the Printed Wiring Board [PWB] and all the components attached to the PWB, also called a Circuit Card Assembly [CCA] refer right. Also refer to PWB Terms [within the PCB Dictionary].

Assertion. When the output of an IC is taken to Voh, in a single-ended device, assuming an active high logic circuit [positive logic]. When the +side of a differential circuit is taken to Voh and the -side of the same differential circuit is taken to Vol for the same signal.

Assigned Frequency. The center of the assigned frequency band assigned to a station. The frequency of the center of the radiated bandwidth. The frequency coinciding with the center of an authorized bandwidth of emission. The center of the frequency band assigned to a station.

Assigned Frequency Band. The frequency band within which the emission of a station is authorized; the width of the band equals the necessary bandwidth plus twice the absolute value of the frequency tolerance.

Astable Circuit. A circuit that continually switches between one of two unstable states.

Astable Multivibrator. A multivibrator that has no stable state. Also called free-running because it alternates between two different output voltage levels during the time it is on. The frequency is determined by the RC time constant of the coupling circuit. Also refer to a 555 Astable Circuit, or Transistor Astable Multivibrator Circuit, or the transistor schematic in the side-bar. A CMOS 4047 integrated circuit.

Astigmatism. An aberration of a lens with spherical surfaces such that the image of a point not lying on the optical axis is a pair of short lines normal to each other and at slightly different distances from the lens. Radial and tangential lines are in focus in different image planes.

Asymmetrical filter. A band-pass filter having different skirt slopes on the two sides of the pass band. A filter that rolls-off at one rate at the lower band, and rolls off at a different rate at the upper band.

Asymmetrical Multivibrator. A multivibrator that generates rectangular waves.

Asymptote. A line that approaches a curve but never touches it.

Async. Short for Asynchronous. Transmission that has no fixed time frame between characters.

Asynchronous. Having no timing relationship.

Asynchronous Communication. Communication in which no clocking information is passed between stations.

Asynchronous Communications System. A data communications system that uses asynchronous operation. Normally extra signal elements [Start, Stop bits] are usually appended to the data for the purpose of synchronizing individual data characters or blocks.

Asynchronous Input. An input on a flip flop or some other clocked device that does not require a clock to determine the output of the device, as in a Clear signal.

Asynchronous Logic. A Digital circuit whose output only depends on the combination logic gates used and the propagation delay through those gates. A logic circuit that does not use a Flip Flop or other synchronizing element.

Asynchronous Network. A network in which the clocks do not need to be synchronous or mesochronous.

Asynchronous Operation: A sequence of operations in which operations are executed out of time coincidence with any event. An operation that occurs without a regular or predictable time relationship to a specified event.

Asynchronous Reset. A component that will rest, regardless of the state of the clock, any time a reset signal is received.

Asynchronous Transfer Mode. [ATM] An association established by the ATM Layer to support communication between two or more ATM service users (i.e., two or more next higher layer entities or two or more ATM Management entities). The communication over an ATM Layer connection may be either bidirectional or unidirectional. When bidirectional, two virtual channel connections (VCCS) are used. When unidirectional, only one VCC is used.

Asynchronous Transmission. Data transmission that does not pass clocking information to align the data; Parallel Information is synchronized individually [per transfer] by hand-shaking as in DAV [Data Available] and DAC [Data Accepted], or REQ and ACK lines. Serial Information is synchronized individually [per block] via 'START' and 'STOP' bits. Information is passed between nodes with out a separate clock signal to indicate when data on the transmission line is valid.