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Using PID Auto tuning VI

I woul like to know  a little bit more about the PID Auto Tuning VI.  I read (in the user's manual) that it uses the Ziegler-Nichols method. I know that this method increases de Kc (gain) parameter until the system becomes oscillatory and then with that Kc and the period of the oscillations Tu you find the PID gains.  I would like to know how the VI increases the Kc, and if it increases de Kc until the system is oscillatory.
 
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Hi Yen78,

Yes, the PID Auto Tuning vi increases the Kc gain parameter till system output becomes oscillatory. Page 2-6 of the manual http://digital.ni.com/manuals.nsf/websearch/A25258DF0D3E3CB386256B41000BA9B9 gives more information on this. You can also open the block diagram of the PID Auto Tuning vi and specifically look at the PID Relay Auto Tune.vi to see how the code is written. This tutorial has a section on Tuning which is also informative http://zone.ni.com/devzone/conceptd.nsf/webmain/d4748f0d59cf436d8625702700809ef4#3

Hope this helps!

Regards,
Prashanth

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Hello,

I was hoping to get some insight on this vi.

I have the s/w and h/w set up and it is stable. So now we can attempt autotuning. We start the wizard, with the PV very close to SP, and do the noise thing and then we wait for three full cycles to get the OK to contunue. But... yesterday awaiting the three cycles we waited from 2:30PM to midnight - close to 10 hours. That's when I decided to stop it and start asking questions. Does this sound right?

Meanwhile the systems keeps close to the SP. The setup is a furnance control system.

Suggestions please?

Many thanks.

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