INTRODUCTION

A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial control systems which are used for controlling processes or machines.

There are two main types of control loops: Open loops, which operate with human input, and closed loops, which are fully autonomous. Some loops can be switched between closed and open modes. When open, a switchable loop is manually controlled and when closed it is fully automated.

Programmable logic controllers (PLCs), programmable automation controllers (PACs), remote terminal units (RTUs), control servers, intelligent electronic devices (IEDs) and sensors are some of the elements of control loops that are in turn a part of control systems. The control loops that make up control systems are generally made themselves of a sensor, a controller and a final control element. The sensor reads the process variable or a related measurement. The controller receives the signal from the sensor and then forwards it to instrumentation, to remote terminal units and to final control elements where the process variable is adjusted, to be kept constant at what is known as a set point.