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What is meant by derivative time?

The intensity of the D component (differential component) can be set via the derivative time. The D component of a controller with PID or PD action reacts to the rate of change of the process value.
When the setpoint is approached, the D component acts as a brake, thereby preventing the control variable from overshooting the setpoint.
Basically, the D component has the following effects:
As soon as the control variable changes, the D component reacts against this change.
For a controller with an inverse operating sense (i.e. for heating) this would mean, for example

  • if the control variable decreases as a result of a disturbance in the process, the D component forms a positive manipulating variable, which counteracts the reduction in control variable.
  • if the control variable increases as a result of a disturbance in the process, the D component forms a negative manipulating variable, which counteracts the increase in control variable.
    The damping action increases with the size of the setting for the derivative time (value in seconds).