Controllers in Industrial Control Systems

Controllers in industrial Control systems

A controller receives information about a process, makes a decision based on this information, performs some action on the process, and monitors the results. This basic concept has not changed with changes in technology, but several technologies have been developed to perform the controller functions over the years.

Relay logic and pneumatic controls are two technologies that are still in widespread use. Relay logic control finds application in automation of sequential type machines while pneumatic control usually is found in automation of proportional control of a continuous process.

Both sequential and proportional process types can be handled by a relatively new product; programmable electronic controllers based on solid-state programmable processors. The availability of low-cost, reliable, solid-state electronic components and processors has made the electronic programmable controller the leader in industrial control.

In electronic programmable controllers, the instructions are stored in a memory and the instructions can be changed easily and quickly. To change instruction in a relay or pneumatic controller requires physical wiring or tubing changes which often is difficult, expensive, and time consuming, if it is possible at all.

There are two types of controllers available to perform industrial control. The most basic is the sequence controller which is concerned with the ordering of a control process and deals with ON/OFF control signals that occur step by step or in repeated steps, or in a combination of the two, to accomplish a task. The second is the process controller which is concerned with the control of a continuously variable process such as might be encountered in continues manufacturing plants.