Control sensitivity function (Su)
Describes the frequency dependent amplitude gain of disturbances that are affecting the set point (SP), more specifically their influence on the controller output MV. To ensure that no disturbances are gained "too much" by the controller the control sensitivity function upper limit must be taken into account. For good performance, it should be less than 2. The importance of control sensitivity function increases when the setpoint is generated by the superior controller in cascade control structure. (see the signals notation)
There is in principle no possibility to compute some robustness regions for control sensitivity function (Su). However, you can check this function in PID Control Laboratory where you can also shape it interactively by hand.
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