In automatic mode, the manipulated variable Y is determined through the discrete PID closed-loop control algorithm subject to 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 this, there are two exemplary possibilities shown for a PID controller.

In manual mode the manually manipulated value YMAN is passed on directly to the manipulated variable 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 this operating mode the D component is automatically set to 0.

In halt mode the control output remains unchanged; the function block does not influence the manipulated variable Y, i.e. Y = Y(old). Internal variables will be manipulated in such a manner that the controller (with I component enabled) can be driven smoothly from its current position. The control limits are also limits for the Anti-windup reset. The halt operating mode is also useful for setting the control output Y via an external operator device, whereby the internal components are tracked correctly in the controller.

In this operating mode the D component is automatically set to 0.