Integral action accumulating while the output is saturated, causing overshoot when the loop recovers.
Trend showing integral windup: after a period with the output saturated, the process variable overshoots badly and the output stays at its limit long after the setpoint has been reached. The output pinned at a limit for a stretch, then a large overshoot when the setpoint is finally reached, and an output that refuses to come off the limit until the error has been negative for a while. The integral term accumulated while the controller could not act on it.
What it means
When the controller output is sitting at a limit, integral action keeps accumulating even though the output cannot go any further. That stored correction has to unwind before the output will come off the limit.
The symptom is a large overshoot after a period of saturation, with the output staying pinned well after the process variable has crossed setpoint. It looks exactly like aggressive tuning, and detuning in response makes it worse: a slower loop spends longer saturated and therefore winds up further.
Trend showing integral windup: after a period with the output saturated, the process variable overshoots badly and the output stays at its limit long after the setpoint has been reached. The output pinned at a limit for a stretch, then a large overshoot when the setpoint is finally reached, and an output that refuses to come off the limit until the error has been negative for a while. The integral term accumulated while the controller could not act on it.
Also called
On a plant you will hear this called reset windup. They mean the same thing.
Two photos, thirty seconds, no signup. The pre-flight check finds the structural
problems that no amount of tuning will fix — before you touch the controller.