RS 5000 PID Control Loop

When the loop is in software manual, is the manual output (valve %) being set using the .SO word in the PID tag, or directly through the control variable tag? (Cross-reference the control variable tag for any locations other than the PID instruction and/or direct reference from the HMI).

Also, is the PID instruction being periodically scanned (with rung-in true) while in software manual (i.e., it is unconditional in a periodic routine, or does not have anything except the loop timer bit in a continuous routine)?
 
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Yes the valve percentage is being set through the .SO instruction while in manual

The PID is operated once the auto button is true, it does have a timer but it does not control the loop on its own
 
mavrick said:
Yes the valve percentage is being set through the .SO instruction while in manual

The PID is operated once the auto button is true, it does have a timer but it does not control the loop on its own
Click to expand...

OK, well this invalidates the only scenario I could come up with, in light of the previously answered questions. (Namely, the loop output was actually set to zero percent, either by .SO or .MAXO, on the last true scan in SWM, but the valve was non-zero because it was being controlled directly through the control variable tag.)
 
Is it possible that the instruction is some how corrupt and needs to be replaced? Rockwell told me to re-download the program with the most current program file and see if that works. I have exhausted all my options, so i guess i will try it.
 
This is going to be like a game of 20 questions if you can't post the logic.

Can you write a brand new program that is -very- similar to the existing one, using all new tag names, and share that with us? (y)
 
Have you checked the DATA arrays? I've had invalid values in there before which caused the PID to behave erratically. If so, zero them out.
 
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I used the logix compare tool on the PID instruction i noticed that the .dvna had a 1 in it on my old file and the new that is having troubles has a 0 in it.

Also the .DVPA on the old file that was working has a 0 in it and the new that is having issues has a 0 in it. Any significant there?

This morning we switched the valve from manual to auto and everything worked as it should i don't know what was going on yesterday, but as of right know it is working correctly.
 

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