A PLC (Programmable Logic Controllers)  is an industrial computer used to monitor inputs, and depending upon their state make decisions based on its program or logic, to control (turn on/off) its outputs to automate a machine or a process.


NEMA defines a PROGRAMMABLE LOGIC CONTROLLER as: “A digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions by implementing specific functions such as logic sequencing, timing, counting, and arithmetic to control, through digital or analog input/output modules, various types of machines or processes”.

Traditional PLC Applications
In automated system, PLC controller is usually the central part of a process control system.
*To run more complex processes it is possible to connect more PLC controllers to a central computer.

Disadvantages of PLC control
– Too much work required in connecting wires.
– Difficulty with changes or replacements.
– Difficulty in finding errors; requiring skillful work force.
– When a problem occurs, hold-up time is indefinite, usually long.

Advantages of PLC control
* Rugged and designed to withstand vibrations, temperature, humidity, and noise.
* Have interfacing for inputs and outputs already inside the controller.
* Easily programmed and have an easily understood programming language.


This section describes about the PLC history, how it evolved and basic introduction for beginners who want to explore about PLC. More>>

Need of PLC

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Basics of PLC

This section describes and explain about basic PLC architecture, how I/P and O/P modules are mounted…. more>>

Selection Criteria for PLC

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PLC Ladder Diagrams

This section describes about the basics of ladder diagram in PLC… more >>

PLC Instructions

This section describes about the basic instruction we generally use in PLC programming. These instructions are commonly taught in any PLC training program….more>>

Major PLC types

This section describes about different PLC types with their specifications. more >>

Industrial Real time Problems with PLC Ladder Logic

This section will enable our reader to go through different set of problems generally from industrial point of view…. more>>

PLC Installation and Commissioning

This section is a brief guide for PLC installation and commissioning for beginners…. More>>

Troubleshooting and Fault detection in PLC

This section describes about different problems which can occur in a PLC and methods to teoubleshoot…. more>> 

PLC terminology

This section is having a list of different words generally used in PLC world and their meaning….. More>>

PLC Interview Basics

This section is a compilation of some generous interview questions generally asked to Automation/PLC engineer… more>>