PLC is short for Programmable Logic Controller.

A PLC is an industrial computer, used for controlling processes in a factory.

Programmable Logic Controllers have advantages over the original hard-wired systems, used in early factories.

The introduction of electricity into factories, heralded the industrial era, referred to as ‘Industry 2.0’.

Early Industry 2.0 factories had ‘hard wired’ control systems.

This meant that once installed, it was expensive to make changes to how the factory production operated.

An example of a hard-wired system is a Star-Delta Starter system.

Once the Star-Delta starter has been installed, the only way to modify it, is by physically rewiring the hardware.

Industry 3.0 introduced Automation, Robotics, and IT systems into the factory.

With Industry 3.0 came the introduction of the PLC in the 1960’s.

PLC systems are programmable, and therefore production systems can be modified cheaply and easily, compared with the original hard-wired systems.

System Process

The basic blocks of a PLC control system, consist of three distinct stages.


The inputs into the PLC, come from control sensors around the factory.


The process stage occurs inside the PLC, and is where the system decides what to output, based on what is being inputted.


Outputs from the PLC control devices such as Induction motors (via contactors etc), and robotic production systems.

Ladder Logic

Coming soon….

Published by Craig Miles

Craig Miles

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