Notes on Controller Settings
IP244
C79000–B8576–C860–02
4–130
PD controller
D control elements alone are unsuitable for control, since they no longer output an actuating signal
when the input variable returns to a static value.
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In conjunction with P control elements, the D action is used to generate an actuating pulse
dependent on the speed of change of the controlled variable. If a disturbance variable z influences
the control system, the PD controller sets itself for a different system deviation as a result of the
changed degree of correction. Disturbances are not completely corrected. The advantage is the
good dynamic response. During start-up and when changes occur in the reference variable, a
well-damped and oscillation-free transition is achieved. A controller with a D action is, however, not
suitable for controlled systems with pulsating measured values, e.g. pressure or flow controls.
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