In automatic mode the control output Y is determined through the closed-loop control based on the controlled variable PV and reference variable SP. The manipulated variable is limited by ymax and ymin. The control limits are also limits for the Anti-windup reset.

The changeover from automatic to manual is normally not bumpless, since output Y can take on any value between ymax and ymin, and Y goes directly to YMAN at the changeover.

If the changeover from automatic to manual is to be bumpless in spite of these problems, there are two exemplary possibilities shown for a PID controller.

In manual mode the manually manipulated value YMAN is passed on directly to the control output Y. However, the manipulated variable is limited by ymax and ymin. Internal variables will be manipulated in such a manner that the controller changeover from manual to automatic (with I component enabled) can be bumpless. The control limits are also limits for the Anti-windup reset

In halt mode the control output remains unchanged; the function block does not influence the control output Y, i.e. Y = Y(old). Internal variables will be manipulated in such a manner that the component sum corresponds with the manipulated variable, thus allowing the controller to be driven smoothly from its current position. The control limits are also limits for the Anti-windup reset. Halt mode is also useful in allowing an external operator device to adjust control output Y, whereby the controller's internal components are given the chance to continuously react to the external influence.