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

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7.3. Effect of Process Parameters on Bode and Nyquist Plots

In this section we stress the effect of process parameters and the concepts of “all-pass” and “nonminimum phase.”

Effect of Process Order

Consider the following first-, second-, and third-order transfer functions.

The Bode plot is shown below in Figure 7-6. The higher order transfer functions have amplitude ratios that decrease more rapidly with frequency, and the phase angles asymptotically approach larger (more negative) values (−180° and −270° for the second- and third-order processes).

Figure 7-6. Bode plots. Comparison of first-, second-, and third-order systems with a gain of 1 ...

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