Control System Fundamentals

A control system is the hardware and software that controls an automated process. Control systems are made up of controllers, input devices, and output devices.

Controllers

The controller is the brain of a control system. It makes decisions for the system based on a set of rules that are programmed by controls engineers.

You may hear controllers being referred to as processors, programmable controllers, programmable logic controllers (PLCs), and Programmable Automation Controllers (PACs).

I/O Modules

I/O modules, or input/output modules, allow a controller to interact with the physical world.

Input modules convert electrical signals from input devices into digital signals that can be understood by the controller. Examples of input devices are buttons and temperature sensors.

Output modules convert digital signals from the controller into electrical signals that control output devices. Examples of output devices are lights and motors.

Controlling a Process

To control a process, the controller;

Reads the status of its inputs to determine the state of a process. For example, the controller may see that the input corresponding to a start button is True.

Executes the program that has been downloaded to it. This program tells the controller what to do when certain inputs are active. For example, the program may specify that a conveyor should run when the start button is pressed.

Updates its outputs to control the process. For example, the controller may turn on an output that causes a conveyor to run.

This process is repeatedly cyclically.

Wrap Up

There are many different types of controllers available from different manufacturers.

Each type of controller has different capabilities and is programmed with different software, but they all work in the same basic way that is outline here.