Programmable Logic Controllers are used to continuously monitor the input values of sensors and generate outputs for actuator operations according to a program. Each PLC system contains the following three modules:
Central Processor Module
A power supply module
One or more I/O modules
Central Processor Module:
The CPU module consists of the central processor and its memory. The processor is responsible for performing all necessary data calculations and processing by accepting inputs and generating appropriate outputs.
Power Supply Module:
This module provides the required power for the entire system by converting available AC power to the DC power required by the CPU and I/O modules.5V DC output drives the computer circuitry.
Input/Output Module:
The input and output modules of a programmable logic controller are used to connect sensors and actuators to the system to sense various parameters such as temperature, pressure, and flow. These I/O modules are of two types: digital or analog.
Communication Interface Modules:
These are intelligent I/O modules that transfer information between the CPU and the communication network. These communication modules are used to communicate with other PLCs and computers placed in remote or distant locations.
The program in a Programmable Logic Controller CPU consists of an operating system and a user program. The purpose of the operating system with the CPU is to handle PLC tasks and operations such as start and stop operations, memory areas and communication management. User programs are used by the user to accomplish and control automation tasks.
The working principle of PLC can be understood in terms of cyclic scanning, also known as scanning cycle