Industrial Automation Abbreviations (Glossary)


Programmable Logic Controller


Human Machine Interface


Man Machine Interface




Original Engineering Manufacturer


Real Time Clock, This refers to a built in clock that has time relative to the time of that in the real world


“Structured Query Language” is a special purpose programming language for managing data held in a relational database

Unitary PLC

A “Unitary PLC” is also more commonly referred to as a brick PLC due to its standalone appearance.

A Unitary PLC is the more simple type of controller, and contains all of the basic system components within a single housing, or box. These components typically include the processor, which runs the software program, in addition to inputs and outputs.

A commonly used example of a unitary PLC type is the Micrologix 1000, built by Allen Bradley. The Micrologix 1000 includes on-board memory for storing programs, 32 digital input and output ports, and a communications port used to program the unit. This setup is typical of many unitary systems.

Bootstrap Mode

“Bootstrap mode” is a state that you can force a PLC to enter on power-up to allow the user to edit certain PLC functions without runnning the loaded program. There are several different ways to enter “bootstrap mode” depending on the PLC you are using.

On Unitronics PLCs; pressing the touchscreen durin power-up will enter Bootstrap mode or if no Touchscreen is available then holding the ‘esc’ & ‘info’ buttons durin power-up will also enter Bootstrap mode.


Transmission Control Protocol/ Internet Protocol, basic communication language for private network or the internet in general

FB Protocol

Function Block Protocol is a piece of repeatable, reusable code in the form of a function block that can be used to simplify more complicated programming tasks such as ASCII communication


Operator PLC, this defines an all in one PLC & HMI unit


OLE for Process control. This is a software interface standard that allows Windows programs to communicate with industrial Hardware devices such as PLCs


Is a standard for Serial Communication data transmission.


Is a standard for digital communication networks and can be used over a long distance in electrically noisy encvironments. RS485 can also be used to communicate with multiple units simultaneously unlike RS232

PID Controller

Proportional Integral Derivative Controller, uses anticipatory control by calculating the amount of error/difference between a user defined set point and actual position used to correct outputs accordingly


The original and most widely used communications system for industrial PLC & controller communications


Is a Controller Area Network, a Bus system designed to allow PLCs and microcontrollers to communicate with each other without the need for a host Computer


Communication system standardised for use mainly in American countries


Simple Network Management Protocol, is a protocol for network management. Used to confiigure and gather information from devices on an ‘Internet Protocol’ Network