Control loop glossary

Anti-reset windup

Controller logic that stops integral action accumulating while the output is at a limit.

A loop that consistently performs poorly and consumes disproportionate attention.

Making a deliberate step change to a loop and observing the response.

Switching a controller between manual and automatic without the output jumping.

Two controllers in series, where the outer loop sets the setpoint of a faster inner loop.

The delay between a change at the output and the first sign of a response in the measurement.

A range of signal change that produces no movement at the valve at all.

Changing the controller tuning automatically as a function of operating point.

A control loop cycling continuously around setpoint instead of settling.

A difference in valve position for the same signal depending on which direction it was approached from.

Integral action accumulating while the output is saturated, causing overshoot when the loop recovers.

A tuning method that sets the closed-loop response time to a chosen value rather than maximising speed.

A sustained oscillation of constant amplitude caused by a nonlinearity rather than by tuning.

A steady difference between the process variable and setpoint that does not close.

How much the measurement moves for a given change in controller output.

A traditional tuning target where each oscillation peak is a quarter the size of the one before.

Static friction that stops a valve stem moving until the signal change is large enough to break it free.