Principles of Process Control
A. Bhatia, B.E.
The kinds of processes
found in industrial plants are as varied as the materials they produce. They
range from the simple loops to control flow rate, to the large and complex distillation
columns in the petro-chemical industry. Today the application of feedback control
loops is an essential element in virtually every industrial product, yet this
feedback control loop which is so important to industry is based on a few very
simple and easily understood principles. This course discusses this control
loop, its basic elements, and the basic principles of its application.
This 3-hr course material is based entirely on US Department of Energy training materials DOE-HDBK-1013/2-92, Fundamentals Handbook, Instrumentation and Control, Module 7, Volume 2 of 2.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
At the conclusion of this course, the student will:
This course is aimed at students, mechanical, control and process engineers, contractors, estimators, energy auditors, safety personnel, plant layout professionals and general audience.
is the branch of technology that deals in automating, monitoring, and control
of complex processes. The most fundamental element of any automatic control
system is the basic feedback control loop. One basic concept is that for the
automatic feedback control to exist, the automatic control loop must be closed.
This means that information must be continuously passed around the loop.
In performing the control function, the automatic controller uses the difference between the set point and measurement signals to develop the output signal to the valve. The accuracy and responsiveness of these signals is a basic limitation on the ability of the controller to correctly control the measurement. If the transmitter does not send an accurate signal, or if there is a lag in the measurement signal, the ability of the controller to manipulate the process will be degraded. At the same time, the controller must receive an accurate set point signal. To control the process, the change in output from the controller must be in such a direction as to oppose any change in the measurement value.
In this course, you are required to study the following DOE-HDBK-1013/2-92, Fundamentals Handbook, Instrumentation and Control, Module 7, Volume 2 of 2. The concepts and terminology described herein are intended to provide a general explanation of the automatic control fundamentals and their applications in the production processes of the industry.
is based entirely on US Department of Energy training materials (US Department of Energy training materials DOE-HDBK-1013/2-92, Fundamentals Handbook, Instrumentation and Control, Module 7, Volume 2 of 2).
The link to the document is Principles of Process Control.
This web training
module has described the responses of a three mode controller when it is used
in the feedback control of industrial measurements. The reader should have a
clear understanding of the following points.
1) In order to achieve automatic control, the control loop must be closed.
2) The proper value of the settings of proportional band, reset, and derivative time depend on the characteristics of the process. Proportional band is the basic tuning adjustment on the controller. The narrower the proportional band, the more the controller reacts to changes in the measurement. If too narrow a proportional band is used, the measurement cycles excessively. If too wide a proportional band is used, the measurement will wander and the offset will be too large.
3) The function of the reset mode is to eliminate offset. If too much reset is used, the result will be an oscillation of the measurement as the controller drives the valve from one extreme to the other. If too little reset action is used, the result will be that the measurement returns to the set point more slowly than possible.
4) The derivative mode opposes any change in the measurement. Too little derivative action has no significant effect. Too much derivative action causes excessive response of the controller and cycling in the measurement.
5) The proportional plus reset plus rate (PID) controller combines the three individual modes to achieve the advantage of each. The proportional action responds to the error amplitude, the integral action eliminates the offset error and the derivative action provides stability to the process.
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.