FF positioner has built in PID controller. PV value for PID controller is from FF transmitter on same segment. I am facing a problem of PID controller switching from AUTO mode to MANUAL mode on its own. Can some one provide clue where is the problem?

 

One thing that you can cause this (depending on how the PID block is configured) is the PV value from the transmitter not being received, or the PV value temporarily having a Bad Quality\Status, or possibly also High or Low Limited.

 

Thanks for your clue. I tried replacing the transmitter but intermittently similar thing happens. Can it be issue with Fieldbus?