ControlLogix PID question

[Colt Hero]

Why is my PID .PV (Process Variable) getting continually overwritten with some strange value every time the rung my PID Instruction is on goes TRUE (executing)?

Just one rung above is a MOV instruction that copies the PT instrument input to the .PV, but the source and destination are different because the PID seems to be overwriting its .PV value internally.

I've placed an AFI just in front of the PID to prove this behavior (ie: the MOV instruction then shows the same value in both source and destination), but I have no idea where the strange value is coming from. The .PV is only written to by the MOV instruction immediately above.

Is the PID writing this value internally? Tracking is NOT active, BTW

 

[jkerekes]

Scaling?

 

[Colt Hero]

Scaling?

Doesn't seem to be. It's scaled on the card as 4-20 ma equal to 950 to 1100

 

[jkerekes]

Scaling in the PID instruction.

 

[Colt Hero]

That did it. Thanks!