Programmable logic controllers( PLC) are computers used for automation, continuous monitoring and control of industrial control systems( ICS). PLC controllers operate in real-time mode, they provide cyclic processing of automation data and control the state according to customer specifications.
PLC controllers improve the control of processes and can collect important process data and communicate with other units. They can be assembled from various PLC modules to suit the application. These include the module for the power supply, the module connected to the central processing unit, the communication module for the transmission of data, the input and output modules for analog and digital inputs and outputs, and the clock module. In this context, for example, the module with the central unit executes a program with control instructions. Another module provides communication with the I/O devices, programming devices, and with other Programmable Logic Controllers.
PLC computers have special programming languages defined in IEC 61131. These include Ladder Logic, Function Block Diagram (FBD), Structured Text( ST), Instruction List( IL) and Sequential Function Chart (SFC).
PLC controllers can operate as stand-alone units or within a process controlsystem ( PCS). They have no mechanical components and are particularly suitable for repetitive processes. PLC computers control processes while collecting data that is used in feedback to make changes and improvements to control processes.
Unlike the earlier mechanical controls, the electronic PLC controllers can perform customized and complex tasks. They are also much more reliable and can operate for extended periods of time without requiring maintenance.