¹⁵“Reset windup” which is also known as “integral windup” is what happens when any loop controller possessing reset (integral) action senses a difference between PV and SP that it cannot eliminate. The reset action over time will drive the controller’s output to saturation. If the source of the problem is a control valve that cannot attain the desired position, the controller will “wind up” or “wind down” in a futile attempt to drive the valve to a position it cannot go. In an FF system where the final control element provides “back calculation” feedback to the PID algorithm, the controller will not attempt to drive the valve farther than it is able to respond.