TABLE OF CONTENTS The power of the PID controller is that it can be adjusted to provide the desired behavior on a wide variety of process applications through the judicious choice of one, two, or three parameter values, and with only modest knowledge about the process. Determining acceptable values for these parameters is called "tuning" the controller.
In the process industries, the person who tunes the controller often faces a number of adverse factors. The process dynamics are usually not well known; they probably change with operating conditions; there is often an unwanted signal component (called "noise") on the measurement; the loop may be subject to random load changes; and frequently the interaction between control loops makes it difficult to discern the tuning effects of a particular loop from the interactive response with other loops. Furthermore, the loop tuner often must work on an ongoing process, which allows for only minimal or no experimentation or testing. Given these adversities, the wonder is that so many PID loops provide more or less satisfactory performance. On the other hand, it is probably true that the tuning could be improved for a significant number of all control loops.
In this chapter we will explore both theoretical and practical concepts behind controller tuning. The primary techniques to be covered are these:
trial-and-error tuning
tuning from open-loop test data
tuning from closed-loop test data
improving "as found" tuning (also called " intelligent trial-and-error tuning")
If any one of these techniques were clearly superior to the others,...
