In the automatic mode, the control output Y is determined through the PI closed-loop control, based on the controlled variables PV, PV2 and the reference variables SP, SP2. The control output is limited by ymax and ymin.

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.

The P controller works in manual mode. The PI controller I component is manipulated to permit bumpless switching.

In the manual mode the manual manipulated value YMAN is passed on directly to the control output Y. The control output is, however, limited by ymax and ymin. the integral component of the master controller is tracked in such a way that the controller (on connecting to the I-component) can be switched bumplessly from manual to automatic.

In halt mode the control output remains unchanged; the function block does not influence the control output Y, i.e. Y = Y(old). Halt mode is also useful in allowing an external operator device to adjust control output Y. the internal components are so manipulated that the controller can be driven smoothly from it’s current position. The control output is, however, limited by ymax and ymin.

In fixed setpoint control mode the P controller works in automatic mode and the PI-controller works in halt mode.

The fixed setpoint SP_FIX is passed on directly to the control output of the PI controller Y1 (= SP2). The control output of the PIP controller Y is limited through ymax and ymin. The integral component of the master controller is tracked in such a way that the controller (on connecting to the I-component) can be switched smoothly from fixed setpoint control to automatic.