PID Loop Auto-Tune

[EliWaldner]

We are trying to do an Auto-Tune on a PID loop. We have set Control Type to "PID" and Tuning Algorithm to "Open Loop". The behavior we are seeing, seems to be strange. The Output is bumped a little higher and held there it seems, until the PV plateaus? Is that normal behavior for Auto-Tuning an open loop PID? Attached is a screen shot of the tuning process and the results we get for the tune.
 
What are we doing wrong? Any help would be greatly appreciated! Thanks in advance.

[BobO]

Yes, that's exactly how open loop works. Closed loop cycles back and forth between output of 0 and 100% just until the PV pops over the SP.

[EliWaldner]

Are the results normal too? After the tune, the PID loop does not work at all! All the settings are "minus".....

[pbw]

Is there a specific Reason you're using Open Loop?
I've used Closed Loop on numerous occasions and the results where spot on. What are you trying to control?

[franji1]

Are the results normal too? After the tune, the PID loop does not work at all! All the settings are "minus".....

Is your loop "reverse acting", i.e. when your .Output goes up, your .PV goes down and vice versa?

[franji1]

Also, try to start with your PV is ssomewhat stable, and NOT on the 2 extremes, e.g. put your PID loop in Manual mode, set the .Output to 50.0 and let your process "settle" out (the .Output can be probably be anything between 20.0 and 80.0, just not 0.0, 1.0, 100.0 or 99.0 when you start tuning)