Integral windup

Integral windup refers to the situation in a PID controller where the integral, or reset action continues to integrate (ramp) indefinitely. This usually occurs when the controller's output can no longer affect the controlled variable, which in turn can be caused by controller (the output being limited at the top or bottom of its scale), or if the controller is part of a selection scheme and it is not the selected controller.

Integral windup was more of a problem in analog controllers. Within modern Distributed Control Systems and Programmable Logic Controllers, it is much easier to prevent integral windup by either limiting the controller output, or by using external reset feedback, which is a means of feeding back the selected output to the integral circuit of all controllers in the selection scheme so that a closed loop is maintained..