A programmable logic controller is a special computer device that is used in industrial control systems. It monitors inputs and outputs and makes logic-based decisions for automated processes and machines.

How does a PLC Work?

A central processing unit (CPU) serves as the brain of the PLC. The CPU directs the PLC to execute control instructions, carry out logic, communicate with other devices, conduct arithmetic operations and perform internal diagnostics. The CPU constantly checks the PLC through running memory routines since the PLC controller is redundant and by doing so ensures the memory is not damaged while still avoiding programming errors.

PLCs read signals from different sensors and input devices. These input devices can be keyboards, switches or sensors. They continuously monitor input values from sensors and produce the outputs for the operation of the actuators based on the program.

A PLC system comprises of three modules:

1- CPU Module

Consists of a central processor and its memory. The processor performs all the necessary computations and processes data by accepting the inputs and producing the appropriate outputs.

2- Power Supply Module

This module supplies the required power to the whole system by converting the AC power to DC power required for the CPU.

3- Input /Output (I/O) Module

The input and output modules are used to connect the sensors and actuators to the system to sense the various parameters such as pressure, flow, and temperature.

The program in the CPU consists of an operating system and user programs. The purpose of the operating system is to deal with the tasks and operations of the PLC such as starting and stopping operations and communication management. A user program is used for finishing and controlling the tasks in automation.

Programmable Logic Controllers Applications

Different applications of Programmable Logic Controllers are:


Conveyor belts are used in most manufacturing plants due to their convenience and uniform motion. They are also found in airports where they transport luggage on carousel until you claim it, there are giant conveyor systems that are used in the construction industry for transporting material.


The PLC controls the roller coaster where people go to find thrill in height and speed. The PLC control is for taking the cars up before the big drop. It also prevents the cars from moving in the reverse direction as a safety measure.


Also known as touchless car wash, every process is calculated and carefully controlled by PLCs. Water is mixed with cleaning solutions, blasted on the surface of the vehicle while spinning wipers scrub it. From the liters of soap used to the length of time the wipers spend spinning, they are automated by the PLC and by doing so saves on time and workforce since the only human interaction is the pressing of a button at the entrance.


They are largely used to control the material ratio and also produce flat glasses.  Bus technology is used to construct the control mode of the PLC with a distributed control system. This control system enables digital quality control and position control.


PLCs are used for various processes in the paper industry. For example,  PLC monitors and controls the production of book pages. It controls the machine that produces paper at high speeds.

Where can I get PLC devices?

Different types of PLCs are available from a large number of manufacturers in the market. One can find a detailed PLC of his choice on online platforms from the variety of retailers and distributors available.