# Errata: In Example 12.9, poles are at -a, -p1, -p2

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Location: page 364, line -10 to -4

There are several errors associated with the sign of the poles in Example 12.9. The pole for the loop transfer function is at and the closed loop poles are at and . In some portions of the text, these are written without the negative sign. The correct text after the fourth displayed equation should read

Assume that the process pole is much more negative than the closed loop poles and , say, . Notice that the proportional gain is negative and that the controller has a zero in the right half-plane if , an indication that the system has bad properties.

Next consider the sensitivity function, which is 1 for high frequencies. Moving from high to low frequencies, we find that the sensitivity increases at the process pole .

(Contributed by H. Yin, 12 May 09)