Page 417 - Programmable Logic Controllers, Fifth Edition - Mobile version

DIP switch A group of small, in-line on-off switches. From dual
in-line package. Energize The physical application of power to a circuit or device to
activate it; the act of setting the on, true, or 1 state of a programmable
Direct addressing An addressing mode in which the memory logic controller’s relay ladder diagram output device or instruction.
address of the data is supplied with the instruction. Erasable programmable read-only memory (EPROM) A
Discrete I/O A group of input and/or output modules that operate programmable read-only memory that can be erased with ultraviolet
with on/off signals, as contrasted to analog modules that operate with light, then reprogrammed with electrical pulses.
continuously variable signals. Error signal A signal proportional to the difference between the
actual output and the desired output.
Disk drive The device that writes or reads data from a magnetic
disk. Ethernet A network type or protocol that uses the Carrier Sense
Multiple Access Collision Detection (CSMA/CD) network access
Diskette The flat, flexible disk on which a disk drive writes and reads.
method.
Display The image that appears on a cathode-ray tube screen or on Ethernet/IP An open industrial networking standard that takes
other image projection systems.
advantage of commercial off-the-shelf Ethernet communication
Display menu The list of displays from which the user selects specific devices and physical media; IP refers to industrial protocol.
information for viewing.
Even parity When the sum of the number of 1s in a binary word is
Distributed control A method of dividing process control into several always even.
subsystems. A PLC oversees the entire operation.
Examine if closed (XIC) Refers to a normally open contact instruction
Divide A programmable logic controller instruction that performs a in a logic ladder program. An examine if closed instruction is true if its
numerical division of one number by another. addressed bit is on (1). It is false if the bit is off (0).
Documentation An orderly collection of recorded hardware and Examine if open (XIO) Refers to a normally closed contact instruction
software data such as tables, listings, and diagrams to provide reference in a logic ladder program. An examine if open instruction is true if its
information for programmable logic controller application operation addressed bit is off (0). It is false if the bit is on (1).
and maintenance. Exclusive-OR gate A logic device requiring one or the other, but
Done bit (DN) Bit that is set to 1 when the instruction has completed not both, of its inputs to be satisfied before activating its output.
its task, such as reaching its preset value. Execution The performance of a specific operation accomplished
Double precision The system of using two addresses or registers through processing one instruction, a series of instructions, or a
to display a number too large for one address or register; allows the complete program.
display of more significant figures because twice as many bits are used. Execution time The total time required for the execution of one
Down-counter A counter that starts from a specified number and specific operation.
increments down to zero.
Download Loading data from a master listing to a readout or another F
position in a computer system. False As related to programmable logic controller instructions, a
Dry-contact-output module Enables a PLC’s processor to control disabling logic state.
output devices by providing a contact isolated electrically from any Fault Any malfunction that interferes with normal operation.
power source.
Fault indicator A diagnostic aid that provides a visual indication
E and/or an internal processor software indication that a fault is present
in the system.
Edit The act of modifying a programmable logic controller program Fault-routine file A special subroutine that, if assigned, executes
to eliminate mistakes and/or simplify or change system operation.
when the processor has a major fault.
Electrically erasable programmable read-only memory Feedback In analog systems, a correcting signal received from the
( EEPROM) A type of programmable read-only memory that is output or an output monitor. The correcting signal is fed to the controller
programmed and erased by electrical pulses. for process correction.
Electrical optical isolator A device that couples input to output Fiber optic cable Transmits information via light pulses down
using a semiconductor light source and detector in the same package. optical fibers.
Electromagnetic interference (EMI) A phenomenon responsible Fieldbus An open, all-digital, serial, two-way communications
for noise in electric circuits. system that interconnects measurement and control equipment such as
Element A single instruction of a relay ladder diagram program. sensors, actuators, and controllers.
Emergency stop relay A relay used to inhibit all electric power to a File A formatted block of data treated as a unit.
control system in an emergency or other event requiring that the controlled Fixed I/O Input/output terminals on a programmable logic controller
hardware be brought to an immediate halt. that are built into the unit and are not changeable. A fixed I/O PLC has
Enable To permit a particular function or operation to occur under no removable modules.
natural or preprogrammed conditions. Floating-point data file Used to store integers and other numerical
Enclosure A steel box with a removable cover or hinged door used values that cannot be stored in an integer file.
to house electric equipment. Flowchart A graphical representation for the definition, analysis,
Encoder A rotary device that transmits position information; a device or solution of a problem. Symbols are used to represent a process or
that transmits a fixed number of pulses for each revolution. sequence of decisions and events.

398 Glossary

pet73842_gls_395-406.indd 398 03/11/15 4:09 PM