5/29/2011 7:33 AM | |
Posts: 53 Rating: (0) |
Please advise how to do offline trending/simulation.. |
5/29/2011 7:54 AM | |
Joined: 1/28/2009 Last visit: 9/10/2024 Posts: 6849 Rating: (1365) |
Hi Please check the attachment,I think the trend roughly illustrates your problem.When you change from manual to auto, and the set less tha PV,algorithm close the valve immidately because of negative error.I am sure that algorithm will settle the process value to the setpoint as illustrated in the attachment.This is natue of PID controller.Please prepare some trends of your process.By the way Your running the PID algorithm with a very small gain. For getting optimum value for P,I and D you can use PID SELF TUNER of SIEMENS.Check here. Regards |
5/29/2011 9:25 AM | |
Joined: 1/28/2009 Last visit: 9/10/2024 Posts: 6849 Rating: (1365) |
You are truly welcome,Also check: PID CONT_C FB41Regards |
Last edited by: hdhosseini at: 5/29/2011 9:26 AM |
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5/30/2011 2:23 AM | |
Posts: 53 Rating: (0) |
Hi Hdhosseini, I've increased the gain and also and Ti and it doesnt seem to help with my PID block.. the LM just goes up to the maximum value or jump to the minimum value. I have just noticed another thing.. When SP>PV.. and i put it in AUTO.. the LMN will increase steadily.. then I put it in MANUAL (LMN is the same as the last AUTO value)... but when I put it back to AUTO.. the LMN value seems to always jump back to either theLMN_P or the sInvAlt.. I have tried this with different setpoint and see the same pattern in all cases.. let's say in AUTO the LMN increase up to 100 (max.) then I change it to MANUAL (LMN stays at 100).. then I change it back to AUTO.----> the LMN always jumps back to the LMN_P or sInvAlt then start increasing from there again.. Please help.. I started to get quite desperate here cos I've only got today to fix this problem.. This may have some relation with the other error that I have(LMN goes to 0 when PV>SP).. Thanks... Please see the attached screenshot of the DB.. note that the value of the LMN on the screenshot is not exactly = to LMN_P as it depends on when I press the 'screenshot' button on my keyboard.. but I am sure it always jump back to there values.. Attachmentpid screenshot.pdf (394 Downloads) |
5/30/2011 6:33 AM | |
Posts: 53 Rating: (0) |
Hi, I have checked the other PID loop that I have on the code and they are all behaving similarly... Once we move from MAN back to AUTO ---> LMN always move to LMN_P (and i found out that LMN_P = error * gain) what is this LMN_P?? Attached is the latest code.. it has not changed since the weekend.. I know now why my gain value is very small... is it because my PV and SP is set to 0-27648? thanks. MS AttachmentPid_test (2).zip (399 Downloads) |
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