TABLE OF CONTENTS This chapter is an introduction to different process control concepts and will help you understand and become familiar with the different process control actions.
The topics covered in this chapter are as follows:
Concepts of signal control and controller modes
Concept of lag time, error signals, and correction signals
ON/OFF types of process controller action
Proportional, derivative, and integral action in process controllers
ON/OFF pneumatic control systems
ON/OFF electric controllers
Pneumatic proportional, integral, and derivative (PID) controllers
Analog electronic implementation of proportional, derivative, and integral action
An electronic PID loop
Digital controller system
Control systems vary extensively in complexity and industrial application. Industrial controllers, for instance, in the petrochemical industry, automotive industry, soda processing industry, and the like, have completely different types of control functions. The control loops can be very complex, requiring microprocessor supervision, down to very simple loops such as those used for controlling water temperature or heating, ventilation, and air-conditioning (HVAC) for comfort. Some of the functions need to be very tightly controlled, with tight tolerance on the variables and a quick response time, while in other areas the tolerances and response times are not so critical. These systems are closed loop systems. The output level is monitored against a set reference level and any difference detected between the two is amplified and used to control an input variable which will maintain the output at the set reference level.
Some of these terms have already been defined, but apply to...
