I'm programming an application which has an override control with low select. It is composed of four PIDs which compete to take the control. The PID with the lower output would take the control. Actually I’m converting an old application programmed in PLC5 to ControlLogix. The existing application uses the tieback input of the PID block to avoid the accumulation of integral error while PID has not the control. I mean when other PID has it. That program periodically sets PIDs to manual in order to force PID to compute the tieback input. This has no effect on the PID which has the control. For controllogix, I have planned to use Function Block but I find PIDE block don’t have a Tieback input. Is any way to obtain the same behavior as the olds PID with PIDE. Does anyone have any suggestion?

 

Go to http://www.ab.com and search for PIDE. You should find a White Paper called logix-wp008_-en-p.pdf which details use of the PIDE instruction including a select application like yours. The quick answer is you don't need to put the other loops in manual, just tie their CVPrevious pin to the CV of the currently selected PIDE.

Hugh