The most commonly used model to describe the dynamics of chemical processes is first order + time delay. In this module, we relate the stability of feedback control of these processes to frequency-response analysis. The important principles that we wish to illustrate are as follows:
Gain margin is a measure of gain uncertainty that can be tolerated
Phase margin is a measure of the time-delay uncertainty that can be tolerated
The “cross-over frequency” is related to the ultimate period from the closed-loop Ziegler-Nichols approach
Ziegler-Nichols recommended tuning values do not provide adequate gain and phase margins
IMC-based PI is easier to tune for robustness than are the other approaches
The sections ...