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 s = − a and the closed loop poles are at s = − p1 and s = − p2. 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 − a is much more negative than the closed loop poles − p1 and − p2, say,
. Notice that the proportional gain is negative and that the controller has a zero in the right half-plane if a > p1 + p2, 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 s = − a.
(Contributed by H. Yin, 12 May 09)
