Siemens SIMATIC S5 Manual page 196

Notes on Controller Settings
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.
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.
IP244
4–130
C79000–B8576–C860–02