Print this page Principles of Process Control
A. Bhatia, B.E.
Course Outline
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.
Learning Objective
At the conclusion of this course, the student will:
- Describe the process control terms such as input/output, open/closed loop systems, feedback, controlled variable and manipulated variable;
- Describe the operation of a control loop diagram including the controlled system, controlled elements, feedback elements, reference point, controlled output , actuating signal and turbance;
- Explain how capacitance, resistance and transportation time affect a control systems lag time;
- Describe the characteristics of two position, proportional and integral control;
- Describe the characteristics of proportional plus reset control system;
- Describe the characteristics of proportional plus rate control;
- Describe the characteristics of proportional plus reset plus rate control;
- State the purpose of setpoint indicator, setpoint adjustment, deviation indicator, output meter, manual-automatic transfer switch;
- Describe the operation of a self balancing control station; and
- Describe the
various types of actuators including pneumatic, hydraulic, solenoid and electrical
operated.
This course is aimed at students, mechanical, control and process engineers, contractors, estimators, energy auditors, safety personnel, plant layout professionals and general audience.
Course Introduction
Process Control
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.
Course Content
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.
Course Summary
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.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
