Two major issues of concern with the close loop operation with P-I-D controllers are the Integration Windup and the requirement of providing Bumpless Transfer.
These two issues are briefly elaborated below. The methodologies for providing Anti-integration Windup and Bumpless Transfer.
A significant problem with integral action is that when the error signal is large for a significant period of time. This can occur every time when there is large change in set point.
If there is a sudden large change in set point, the error will be large and the integrator output in a P-I-D control will build up with time.
As a result, the controller output may exceed the saturation limit of the actuator. This windup, unless prevented may cause continuous oscillation of the process that is not desirable.
When a controller is switched from manual mode to auto-mode, it is desired that the input of the process should not change suddenly.
But since there is always a possibility that the decision of the manual mode of control and the auto mode of control be different, there may be a sudden change in the output of the controller, giving rise to a sudden jerk in the process operation.
Special precautions are taken for bumpless transfer from manual to auto-mode.