RSLogix 500 / ML 1400 PID Loop Anomoly

[morrisma 0]

I have a PID loop controlling a flow control valve based on desired fluid flow. In the idle state, I set the flow control valves to be 100% open. Occasionally, the PD25:0.CVP drops very briefly to zero and recovers back to 100% within 10 seconds. Nothing else around the PID controller changes that I can see. The output 4-20mA signal to the flow control valve does not move. This happens when the PID loop is running as well. For instance, the FCV will be open 20-22% controlling the flow as required when it will drop the CVP % to zero causing the PID loop to snap into action to recover back to 20%.

Anyone ever seen this phenomenon?

[Mickey 71]

 Is there something in the program writing to the output other then the PID instruction? (PD25:0.CV)

Also check for something controlling the auto/manual bit( PD25:0.AM)

Post your program, its .RSS file and someone can help you look.

 

Edited 14 Jun 2016 by Mickey