ere 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.
AC contactor - a contactor designed for AC power.
acceptance test - a test for evaluating a newly purchased systems performance, capabilities, and conformity
to specifications, before accepting, and paying the supplier.
accumulator - a temporary data register in a computer CPU.
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.
acoustic - another term for sound.
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.
A/D - Analog to digital converter (see ADC).
ADC (Analog to Digital Converter) - a circuit that will convert an analog voltage to a digital value, also
refered 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.
address register - a pointer to memory locations.
adsorption - the ability of a material or apparatus to adsorb energy.
agitator - causes fluids or gases to mix.
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 - normal or current environmental conditions.
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. plc glossary - 35.2
analysis - the process of review to measure some quality.
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 suggets 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.
architecture - they general layout or design at a higher level.
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.
aspirator - a device that moves materials with suction.
assembler - converts assembly language into machine code.
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 - to decrease the magnitude of a signal.
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.
attribute - a nongraphical feature of a part, such as color.
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.
automated - a process that operates without human intervention.
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.
35.2 B
B-spline - a fitted curve/surface that is commonly used in CAD and graphic systems.
backbone - a central network line that ties together distributed networks.
background - in multitasking systems, processes may be running in the background while the user is plc glossary - 35.3
working in the foreground, giving the user the impression that they are the only user of the
machine (except when the background job is computationally intensive).
background suppression - the ability of a sensing system to discriminate between the signal of interest, and
background noise or signals.
backplane - a circuit board located at the back of a circuit board cabinet. The backplane has connectors that
boards are plugged into as they are added.
backup - a redundant system to replace a system that has failed.
backward chaining - an expert system looks at the results and looks at the rules to see logically how to get
there.
band pressure Level - when measuring the spectrum of a sound, it is generally done by looking at
frequencies in a certain bandwidth. This bandwidth will have a certain pressure value that is an
aggregate for whatever frequencies are in the bandwidth.
base - 1. a substance that will have an excess of HO ions in solution form. This will react with an acid. 2. the
base numbering system used. For example base 10 is decimal, base 2 is binary
baseband - a network strategy in which there is a single carrier frequency, that all connected machines must
watch continually, and participate in each transaction.
BASIC (Beginners All-purpose Symbolic Instruction Code) - a computer language designed to allow easy
use of the computer.
batch processing - an outdated method involving running only one program on a computer at once,
sequentially. The only practical use is for very intensive jobs on a supercomputer.
battery backup - a battery based power supply that keeps a computer (or only memory) on when the master
power is off.
BAUD - The maximum number of bits that may be transmitted through a serial line in one second. This also
includes some overhead bits.
baudot code - an old code similar to ASCII for teleprinter machines.
BCC (Block Check Character) - a character that can check the validity of the data in a block.
BCD (Binary Coded Decimal) - numerical digits (0 to 9) are encoded using 4 bits. This allows two
numerical digits to each byte.
beam - a wave of energy waves such as light or sound. A beam implies that it is not radiating in all
directions, and covers an arc or cone of a few degrees.
bearing - a mechanical support between two moving surfaces. Common types are ball bearings (light
weight) and roller bearings (heavy weight), journal bearings (rotating shafts).
beats - if two different sound frequencies are mixed, they will generate other frequencies. if a 1000Hz and
1001Hz sound are heard, a 1Hz (=1000-1001) sound will be perceived.
benchmark - a figure to compare with. If talking about computers, these are often some numbers that can be
use to do relative rankings of speeds, etc. If talking about design, we can benchmark our products
against our competitors to determine our weaknesses.
Bernoullis principle - a higher fluid flow rate will result in a lower