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Process Control: Modeling, Design, and Simulation by B. Wayne Bequette

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M6.4. Ziegler-Nichols Tuning

The tuning parameters recommended by Ziegler and Nichols (1942) were shown in Table 6-1. Generally, these values are not very robust. The objective of this section is for you to calculate the values of the gain and phase margins for each of these recommended values. Tyreus and Luyben modified the suggested Ziegler-Nichols parameters for increased robustness (see Luyben and Luyben, 1997); these recommended values were shown in Table 6-2.

Recall that the P-only controller tuning recommended by Ziegler and Nichols (1942) results in a controller that has a gain margin of 2 (since the proportional gain is one half of the ultimate gain). This is also shown by the following MATLAB analysis.

 » kc = 3.8/2; » [mag,phase,w] ...

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