Page 414 - Programmable Logic Controllers, Fifth Edition - Mobile version

Glossary

1’s complement The system used to represent negative numbers in a Analog signal Signal having the characteristic of being continuous
personal computer and a programmable logic controller. and changing smoothly over a given range rather than switching
2’s complement A numbering system used to express positive and suddenly between certain levels, as with discrete signals.
negative binary numbers. Analog-to-digital (A/D) converter A circuit for converting a varying
A analog signal to a corresponding representative binary number.
AND (logic) A Boolean operation that yields a logic 1 output if all
Access To locate data stored in a programmable logic controller inputs are 1, and a logic 0 if any input is 0.
system or in computer-related equipment.
Arithmetic capability The ability to do addition, subtraction,
Accumulated value The number of elapsed timed intervals or multiplication, division, and other advanced math functions with the
counted events. processor.
Actuator An output device normally connected to an output module. Array A group of data, of the same type, under a common name.
Examples are an air valve and cylinder.
ASCII-input module Converts ASCII-code input information from an
Address A code that indicates the location of data to be used by a external peripheral into alphanumeric information a PLC can understand.
program, or the location of additional program instructions.
ASCII-output module Converts alphanumeric information from the
Algorithm Mathematical procedure for problem solving. PLC into ASCII code to be sent to an external peripheral.
Alias tag References a memory location that has been defined by Asynchronous Recurrent or repeated operations that occur in
another tag. unrelated patterns over time.
Alphanumeric Term describing character strings consisting of any Automatic control A process in which the output is kept at a desired
combination of letters, numerals, and/or special characters (e.g., A15$) level by using feedback from the output to control the input.
used for representing text, commands, numbers, and/or code groups.
Auxiliary power supply A power supply not associated with the
Alternating current (AC) input module An input module that processor. Auxiliary power supplies are usually required to supply
converts various alternating current signals originating at user devices logic power to input/output racks and to other processor support
to the appropriate logic-level signal for use within the processor. hardware and are often referred to as remote power supplies.
Alternating current (AC) output module An output module that B
converts the logic-level signal of the processor to a usable output signal
to control a user alternating current device. Backplane A printed circuit board, located in the back of a chassis,
Ambient temperature The temperature of the air surrounding a that contains a data bus, power bus, and mating connectors for modules
module or system. to be inserted in the chassis.
American National Standard Code for Information Interchange Base tag A definition of the memory location at which a data element
(ASCII) An 8-bit (7 bits plus parity) code that represents all characters is stored.
of a standard typewriter keyboard, both uppercase and lowercase, as BASIC A computer language that uses brief English-language
well as a group of special characters used for control purposes. statements to instruct a computer or microprocessor.
American National Standards Institute (ANSI) A clearinghouse Battery indicator A diagnostic aid that provides a visual indication
and coordinating agency for voluntary standards in the United States. to the user and/or an internal processor software indication that the
American wire gauge (AWG) A standard system used for designating memory power-fail support battery is in need of replacement.
the size of electrical conductors. Gauge numbers have an inverse Baud A unit of signaling speed equal to the number of discrete
relationship to size; larger numbers have a smaller diameter. conditions or signal events per second; often defined as the number of
Analog device Apparatus that measures continuous information binary digits transmitted per second.
(e.g., voltage or current). The measured analog signal has an infinite BCD-input module Allows the processor to accept 4-bit BCD
number of possible values. The only limitation on resolution is the digital codes.
accuracy of the measuring device. BCD-output module Enables a PLC to operate devices that require
Analog input module An input circuit that employs an analog-to- BCD-coded signals to operate.
digital converter to convert an analog value, measured by an analog Binary A number system using 2 as a base. The binary number
measuring device, to a digital value that can be used by the processor. system requires only two digits, zero (0) and one (1), to express any
Analog output module An output circuit that employs a digital-to- alphanumeric quantity desired by the user.
analog converter to convert a digital value, sent from the processor, to Binary-coded decimal (BCD) A system of numbering that expresses
an analog value that will control a connected analog device. each individual decimal digit (0–9) of a number as a series of 4-bit

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