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strange problem with PID

5/22/2011 10:34 AM	Rate (0)
e-kuba Posts: 20 Rating: (0)	I wrote a program where I use a PID regulator. When the program startin ewerything is ok and PID works great but few minute or houst leater (time is different) PID switch off. When I conected CPU with PC program is runing, PID input is changing and output is allways zero. What I do wrong?
e-kuba Posts: 20 Rating: (0)
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5/22/2011 10:46 AM	Rate (1)
umencho Diamond Member Joined: 3/21/2006 Last visit: 3/30/2025 Posts: 10239 Rating: (1183)	Hello, It is a difficult to guess what is wrong there remotely. Might be How can you restart a PID controller stopped by sample time failure or disable the sample time monitoring? Best regards, Hristo Mihalev

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5/22/2011 11:58 AM	Rate (0)
e-kuba Posts: 20 Rating: (0)	I don't understand why i must restart PID? Why I must use some different library? Normal PID controler is working wrong? My PID ENO allways is active.
e-kuba Posts: 20 Rating: (0)	Last edited by: e-kuba at: 5/23/2011 5:00 PM Last edited by: e-kuba at: 5/23/2011 5:00 PM
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5/22/2011 1:34 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 3/29/2025 Posts: 6867 Rating: (1367)	e-kuba I don't understand why i must restart PID? Why I must use some different library? Normal PID controler is working wrong? My PID ENO allways is active. Look on the screen. Dear member Output of a Normal PID controller is consisted of 3 elements: proportional part, integration and derivative part.Integration part keeps history of error, in your case as I understood you had negative error in your loop for a long time and this accumulates a negative values and this may not produce a value on manipulated variable of algorithm. Please check you loop for direct (SP-PV>0) or reverse action (PV-SP>0). Regards
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5/23/2011 4:56 PM	Rate (0)
e-kuba Posts: 20 Rating: (0)	Thanks for yours sugestion. I use input filter from http://support.automation.siemens.com/WW/view/en/46163827 . People from technical help in my country tell me about this library. Now I'm waiting it everything will be ok.
e-kuba Posts: 20 Rating: (0)	Last edited by: e-kuba at: 5/23/2011 5:01 PM
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