The PIDER block is a solution for cases where field mounted controllers or field automan stations are installed. For the case of a field PID controller, the following connections would be used. (See document) The S1 input flag would come from the LOCAL/Remote switch with ON = TRACK and OFF = DCS control. TRFB (Tracking feedback) would be connected to the Field PID loop’s local SP (often this is not transmitted back so the PV is used.) The RFB is connected to the PV of the field controller. The RFB value is really a part of the control algo that is designed for cases where a field controller is failing to control to setpoint. It will cause a windup situation in the PIDER, because the feedback value will be different than the output (desired value).
For the case where an AUTOMAN station is installed in the field the connections would be as follows: (See resolution document for diagram) The RFB (reset feedback) and TRFB (Tracking feedback) would be connected to the position feedback from the valve. The S1 input flag would come from the LOCAL/Remote switch with ON = TRACK and OFF = DCS control.
The PV tracking is handled by the S1 input (set by the Field/DCS switch) and the PVTRAKOPTAI flag on the PIDER. The Setting PVTRAKOPTAI =ON will cause SP tracking when the PIDER controller is in AUTO and when S1 is ON. When S1 is ON, the PIDER is in Initialization. The PVTRAKOPTAI flag causes the SP to track the PV when the PIDER is in AUTO and in initialization.
The RFB value does need to be connected to something that normally moves with the PIDER controller output. since it is used to adjust the CV (thus OP) when the Local value is failing to track the requested SP. When the RFB moves with the CV the reset feedback action is zeroed. Normal control reset for the normal PID action is not affected by the RFB.