We've inherited some code from Emerson, where they use an internal reference parameter (pointing to an FFDO READBACK parameter) wired to the DC block F_IN_Dx parameter.
My concern is the FEEDBACK internal reference will go bad on controller switchover, which seems to be the case as we just experienced. However, I'm trying to pinpoint the actual cause of the interlocks activating during switchover, it appears the interlocks that activated are derived from the state of the DC block.
Is my concern warranted?
Several years ago we had a similar issue where a DC block F_IN_Dx parameter did not transfer to the backup controller on a switchover. We tested it several times and confirmed that this was indeed the case. In our case it was the position of a field switch (pump is in auto =1). The backup controller got a 0 on switchover which caused the pump to trip (I don't recall exactly. It could have been that the backup controller saw a transition from a 0 to 1 on the first scan). We did confirm that the DC block's internal parameters do not get transferred over to the backup controller. If I remember right, we resolved this by adding an external parameter to the F_IN_Dx (just like what you have done with FEEDBACK except that this is an external parameter instead of an internal parameter). The external parameter is the DST of the Field Switch. So, I am guessing that if you change FEEDBACK to an external parameter (with the external parameter being the DST of the Fieldbus DO), it might do the trick. I would be interested to know what you find out.