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Glossary A
Absolute Zero: Temperature at which thermal energy is at a minimum. Defined as 0 Kelvin, calculated to be -273.15°C or -459.67°F.

AC: Alternating current; an electric current that reverses its direction at regularly recurring intervals.

Accuracy: The closeness of an indication or reading of a measurement device to the actual value of the quantity being measured. Usually expressed as ± percent of full scale output or reading.

Active Component: A component that provides gain or amplification such as transistor, integrated circuit, valve - such as a triode value. (See passive for opposite)

Adapter: A mechanism or device for attaching non-mating parts.

ADC: (Analog-to-Digital Converter) an electronic device which converts analog signals to an equivalent digital form, in either a binary code or a binary-coded-decimal code. When used for dynamic waveforms, the sampling rate must be high to prevent aliasing errors from occurring.

Address: The label or number identifying the memory location where a unit of information is stored.

Aerial: A length of wire designed to transmit or receive radio waves. (See also Antenna)

AF Audio Frequency: Generally in the range 20Hz to 20KHz.

AFC Automatic Frequency Control: Similar to Automatic Fine Tune (AFT). A circuit that keeps a receiver in tune with the wanted transmission.

Aliasing: If the sample rate of a function (fs) is less than two times the highest frequency value of the function, the frequency is ambiguously presented. The frequencies above (fs/2) will be folded back into the lower frequencies producing erroneous data.

Alphanumeric: A character set that contains both letters and digits.

Alternating Current (AC): An electric current whose direction changes direction with a frequency independent of circuit components.

Alternate Mode: A display mode of operation in which the oscilloscope completes tracing one channel before beginning to trace another channel.

ALU: Arithmetic Logic Unit. The part of a CPU where binary data is acted upon with mathematical operations.

Ambient Compensation: The design of an instrument such that changes in ambient temperature do not affect the readings of the instrument.

Ambient Conditions: The conditions around the transducer (pressure, temperature, etc.).

Ambient Pressure: Pressure of the air surrounding a transducer.

Ambient Temperature: The average or mean temperature of the surrounding air which comes in contact with the equipment and instruments under test.

Ammeter: An instrument used to measure current.

Ammeter: Instrument for measuring the current in amps, milliamps or microamps.

Amplitude Modulation (AM): Where audio signals increase and decrease the amplitude of the "carrier wave".

Amp: Ampere: The unit of electrical current. Also milliamp (one thousandth of an amp) and microamp (one millionth of an amp). One amp corresponds to the flow of about 6 x 1018 electrons per second.

Ampere (amp): A unit used to define the rate of flow of electricity (current) in a circuit; units are one coulomb (6.25 x 108 electronics) per second.

Amplifier: A device which draws power from a source other than the input signal and which produces as an output an enlarged reproduction of the essential features of its input.

Amplitude: 1) The magnitude of a quantity or strength of a signal. In electronics, amplitude usually refers to either voltage or power. It is the highest value reached by voltage, current or power during a complete cycle.  2) A measurement of the distance from the highest to the lowest excursion of motion, as in the case of mechanical body in oscillation or the peak-to-peak swing of an electrical waveform.

Amplitude Span: The Y-axis range of a graphic display of data in either the time or frequency domain. Usually a log display (dB) but can also be linear.

Analog Oscilloscope: An instrument that creates a waveform display by applying the input signal (conditioned and amplified) to an electron beam moving across a CRT screen. A chemical phosphor coated on the CRT creates a glowing trace wherever the beam hits.

Analog : A system in which data is represented as a continuously varying voltage.

Analog Output: A voltage or current signal that is a continuous function of the measured parameter.

Analog-to-Digital Converter (A/D or ADC): A device or circuit that outputs a binary number corresponding to an analog signal level at the input.

AND Gate: Gate that produces a logic 1 when all of its inputs are 1. In all other cases the output is 0.

Antenna: A length of wire or similar that radiates (such as a transmitting antenna) or absorbs (such as a radio antenna) radio waves.

Astable: A circuit that has no stable state and thus oscillates at a frequency dependent on component values.

Angstrom: Ten to the minus tenth meters (10-10) or one millimicron, a unit used to define the wave length of light. Designated by the symbol Å.

Angular Frequency: The motion of a body or a point moving circularly, referred to as the circular frequency O which is the frequency in cycles per second (cps) multiplied by the term (2) and expressed in radians per second (2pf).

ANSI: American National Standards Institute.

Application Program: A computer program that accomplishes specific tasks, such as word processing.

ASCII: American Standard Code for Information Interchange. A seven or eight bit code used to represent alphanumeric characters. It is the standard code used for communications between data processing systems and associated equipment.

Assembler: A program that translates assembly language instructions into machine language instructions.

Assembly Language: A machine oriented language in which mnemonics are used to represent each machine language instruction. Each CPU has its own specific assembly language.

Asynchronous: A communication method where data is sent when it is ready without being referenced to a timing clock, rather than waiting until the receiver signals that it is ready to receive.

ATC: Automatic temperature compensation.

Attenuation: A decrease in signal voltage during its transmission from one point to another.
Audio: A signal that can be heard with the ears.

Automatic Gain Control: A circuit that adjusts the gain of a stage so that the volume is constant even though the input signal may vary over a wide range.

Auto-Zero: An automatic internal correction for offsets and/or drift at zero voltage input.

Averaging: A processing technique used by digital oscilloscopes to eliminate noise in a signal.