Principles for control
2.6 Control Response at Different Feedback Structures
PID control
Function Manual, 03/2017, A5E35300227-AC
31
Equation for PD-action controller
The following applies for the step response of the PD-action controller in the time range:
t = time interval since the step of the control deviation
The derivative action generates a output value as a function of the rate of change of the
process value. A derivative action by itself is not suitable for controlling because the output
value only follows a step of the process value. As long as the process value remains
constant, the output value will no longer change.
The response to disturbances of the derivative action is improved in combination with a
proportional action. Disturbances are not corrected completely. The good dynamic response
is advantageous. A well attenuated, non-oscillating response is achieved during approach
and setpoint change.
A controller with derivative action is not appropriate if a controlled system has pulsing
measured quantities, for example, in the case of pressure or flow control systems.
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