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Industrial Control and Automation terms and Abbreviations (Glossary)

A brief explanation about common terms and abbreviations found within automation Industry to help give you understand PLCs like we understand PLCs

PLC Terms Explained




Programable 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 configure and gather information from devices on an ‘Internet Protocol’ Network


Profibus is a digital network responsible for providing the communication between the field sensors and the control system or controllers. The term ‘Profibus’ stands for ‘Process Field Bus’ and it is the most widely used industrial network worldwide for industrial process control, motion control, automation and safety networks.


Profibus uses a master-slave communication in between the component of the control network. In a master-slave communication, the master includes a unidirectional control on all its slave devices as well as processes.

Profibus Master

The main function of Master devices is to control the bus, so they may transmit messages without any remote request known as active stations.


Profibus Slave

Slave devices are normally peripheral devices like sensors, transmitters and actuators which may allow received messages at the master’s request and send messages to that master, which is known as passive stations.


Profibus DP
(Decentralized Peripherals)

Profibus DP is particularly designed for high-speed data communication in between automation control systems & distributed I/O at the level of the device.


Profibus PA
(Process Automation)

Profibus PA is mainly designed for an automation process. So it allows different sensors as well as actuators connected on a single common bus line even in intrinsically secure regions.





VisiLogic Program file


VisiLogic Display file


VisiLogic Sub Routine file


Previous version Backup file (Created when program created with older version of VisiLogic is opened in a newer version of VisiLogic)


UniLogic Program file


Log single line of date from a data table


Data table structure file for data table export


For DT->SD function blocks stored on SD card


Remote access/operator for monochrome PLC/HMI


Remote access/operator cache file for colour PLC/HMI


Project file only (.v35 – .v57 – .v10)


Project + OS file (.c35 – .C57 – .c10)


Full data table (all 120Kb data table area)


OS files (.O13, .O35, .O57, .O10)


Operand data (.D13, .D35, .D57, .D10)


Free format SD card data block


Trend file


UniDownloader file, for use with UniDownloader application (Enables Download of program to PLC without access through VisiLogic)



*Part Number*-N

The ‘-N’ indicates that this product is unbranded with no Unitronics logo on the front panel of the PLC. In all other aspects these PLCs are exactly the same.

V*Part Number*

The ‘V’ in the product name defines that this unit is from the ‘Vision™’ Series of PLC controllers

*Part Number*-J-*Part Number*

The ‘-J-‘ in the product name defines that this unit is black in colour with a wipe clean front.

SM*Part Number*

The ‘SM’ in the product name defines that this unit is from the ‘Samba™’ Series of PLC controllers


The ‘V200’ modules are snap-in I/O and Communication for the V230, V260, V280, V290, V530, V570, V560, V700, V1040 and V1210 PLCs from the Vision Series


The The ‘V100’ modules are snap-in I/O and Communication for the Samba Series as well as the V120, V130, V350, V430 and V1210 PLCs from the Vision Series

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