Reset Windup

Process Controls PROPORTIONAL PLUS RESET CONTROL SYSTEMS Figure 24 Effects of Disturbance on Reverse Acting Controller By adding the reset action to the proportional action the controller produces a larger output for the given error signal and causes a greater adjustment of the control valve. This causes the process to come back to the setpoint more quickly. Additionally, the reset action acts to eliminate the offset error after a period of time. Reset Windup Proportional plus reset controllers act to eliminate the offset error found in proportional control by continuing to change the output after the proportional action is completed and by returning the controlled variable to the setpoint. An inherent disadvantage to proportional plus reset controllers is the possible adverse effects caused by large error signals. The large error can be caused by a large demand deviation or when initially starting up the system. This is a problem because a large sustained error signal will eventually cause the controller to drive to its limit, and the result is called "reset windup." Because of reset windup, this control mode is not well-suited for processes that are frequently shut down and started up. Rev. 0 Page 35 IC-07