PID Explained for Process Engineers: Part 1 - The Basic Control Equation

January
,
2016

The differential equation for PID control contains three possible modes: proportional, integral, and derivative. This article describes the control equation in language that process engineers can readily understand.

Understanding the process is the key to successful control applications in the process industries. Since process engineers do this far better than anyone else, the logical conclusion is that developing and enhancing control configurations should be the responsibility of process engineers. The counter argument is that process engineers do not have a sufficient understanding of the principles of automatic control to undertake such a task.

Many process engineers lack this understanding because the traditional method of teaching automatic control is not inherently clear. Explanations that rely on the mysterious “s” variable in LaPlace transforms do more to obscure the basic principles than to elucidate them. This article focuses on the time domain (1).

The objective of this three-part series of articles is to explain the proportional-integral-derivative (PID) control equation in language that process engineers, most being chemical engineers, can readily understand. Part 1 focuses on the basic PID equation. Next month, Part 2 examines the tuning coefficients, and in March, Part 3 explains the most common controller features and options.

Author Bios: 

Cecil Smith

Cecil L. Smith has more than 35 years of experience in process control. His primary focus is on designing a control strategy for a processing and then commissioning the controls, that is, the process aspects as opposed to the systems aspects. ...Read more

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