absolute pressure - a pressure measured relative to zero pressure.

absorption loss - when sound or vibration energy is lost in a transmitting or reflecting medium. This is the result of generation of other forms of energy such as heat.

absorptive law - a special case of Boolean algebra where A(A+B) becomes A.

AC (Alternating Current) - most commonly an electrical current and voltage that changes in a sinusoidal pattern as a function of time. It is also used for voltages and currents that are not steady (DC). Electrical power is normally distributed at 60Hz or 50Hz.

acceptance test - a test for evaluating a newly purchased system's performance, capabilities, and conformity to specifications, before accepting, and paying the supplier.

accuracy - the difference between an ideal value and a physically realizable value. The companion to accuracy is repeatability.

acidity - a solution that has an excessive number of hydrogen atoms. Acids are normally corrosive.

acknowledgement (ACK) - a response that indicates that data has been transmitted correctly.

actuator - a device that when activated will result in a mechanical motion. For example a motor, a solenoid valve, etc.

ADC (Analog to Digital Converter) - a circuit that will convert an analog voltage to a digital value, also referred to as A/D.

ADCCP (Advanced Data Communications Procedure) - ANSI standard for synchronous communication links with primary and secondary functions.

address - a code (often a number) that specifies a location in a computers memory.

adsorption - the ability of a material or apparatus to adsorb energy.

AI (Artificial Intelligence) - the use of computer software to mimic some of the cognitive human processes.

air dump valve - this valve will open to release system pressure when system power is removed.

algorithms - a software procedure to solve a particular problem.

aliasing - in digital systems there are natural limits to resolution and time that can be exceeded, thus aliasing the data. For example. an event may happen too fast to be noticed, or a point may be too small to be displayed on a monitor.

alkaline - a solution that has an excess of HO pairs will be a base. This is the compliment to an acid.

alpha rays - ions that are emitted as the result of atomic fission or fusion.

alphanumeric - a sequence of characters that contains both numbers and letters.

ALU (Arithmetic Logic Unit) - a part of a computer that is dedicated to mathematical operations.

AM (Amplitude Modulation) - a fixed frequency carrier signal that is changed in amplitude to encode a change in a signal.

ambient noise - a sort of background noise that is difficult to isolate, and tends to be present throughout the volume of interest.

ambient temperature - the normal temperature of the design environment.

amplifier - increased (or possibly decreases) the magnitude or power of a signal.

analog signal - a signal that has continuous values, typically voltage.

and - a Boolean operation that requires all arguments to be true before the result is true.

annealing - heating of metal to relieve internal stresses. In many cases this may soften the material.

annotation - a special note added to a design for explanatory purposes.

ANSI (American National Standards Institute) - a developer of standards, and a member of ISO.

APF (All Plastic Fibre cable) - fiber optic cable that is made of plastic, instead of glass.

API (Application Program Interface) - a set of functions, and procedures that describes how a program will use another service/library/program/etc.

APT (Automatically Programmed Tools) - a language used for directing computer controlled machine tools.

application - the task which a tool is put to, This normally suggests some level of user or real world interaction.

application layer - the top layer in the OSI model that includes programs the user would run, such as a mail reader.

arc - when the electric field strength exceeds the dielectric breakdown voltage, electrons will flow.

armature - the central rotating portion of a DC motor or generator, or a moving part of a relay.

ARPA (Advanced Research Projects Agency) - now DARPA. Originally funded ARPANET.

ARPANET - originally sponsored by ARPA. A packet switching network that was in service from the early 1970s, until 1990.

ASCII (American Standard Code for Information Interchange) - a set of numerical codes that correspond to numbers, letters, special characters, and control codes. The most popular standard

ASIC (Application Specific Integrated Circuit) - a specially designed and programmed logic circuit. Used for medium to low level production of complex functions.

assembly language - a mnemonic set of commands that can be directly converted into commands for a CPU.

associative dimensioning - a method for linking dimension elements to elements in a drawing.

associative laws - Boolean algebra laws A+(B+C) = (A+B)+C or A(BC) = (AB)C

asynchronous - events that happen on an irregular basis, and are not predictable.

asynchronous communications (serial) - strings of characters (often ASCII) are broken down into a series of on/off bits. These are framed with start/stop bits, and parity checks for error detection, and then send out one character at a time. The use of start bits allows the characters to be sent out at irregular times.

attenuation - as the sound/vibration energy propagates, it will undergo losses. The losses are known as attenuation, and are often measured in dB. For general specifications, the attenuation may be tied to units of dB/ft.

audible range - the range of frequencies that the human ear can normally detect from 16 to 20,000 Hz.

automatic control - a feedback of a system state is compared to a desired value and the control value for the system is adjusted by electronics, mechanics and/or computer to compensate for differences.

auxiliary power - secondary power supplies for remote or isolated systems.

AWG (American Wire Gauge) - specifies conductor size. As the number gets larger, the conductors get smaller.

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