Simplified IMC-PID tuning rules

Abstract

We have significantly simplified the IMC-PID tuning rules. These new rules cover the vast majority of control loops encountered in the chemical industry. This work is the result of a great deal of experience in successfully applying IMC-PID tuning rules and an effort to prepare a training course on controller tuning. The simplified rules are very similar in form to the classic open loop Ziegler-Nichols rules and use the process reaction curve method for process testing. The two differences are that these rules are based on a less aggressive performance criteria and that we adapt the rules for some commonly encountered special cases. This paper presents the relationship between the simplified IMC-PID rules, the general IMC-PID rules, the Ziegler-Nichols rules and the Cohen-Coon rules. We show that the simplified rules are less sensitive to parameter mis-estimation than other more aggressive tuning rules. We also proposed rules for a fourth action; filtering. Filtering is available in digital controllers and smart field transmitters. We report that filtering and derivative action cancel each other and therefore should not be used together. We briefly outline the contents of the tuning course and finish the paper with an industrial example where the simplified rules have been successfully applied.