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PID parameter adjustments

Created by: Raffy at: 10/9/2013 10:56 AM (6 Replies)

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10/9/2013 10:56 AM	Rate (0)
Raffy Posts: 209 Rating: (2)	Hi guys, I am using a PID to for power control and I need some adjustments cause my PID seems to have a hard time catching up with my Set point...my process value has very much a long delay... for example when the PID adjusts and increase the position there is a delay before the power increases..I'm using PID FB41 and FB43..what should be adjusted so that this delay is compensated?? due to this delay the SP and PV would not meet and eventually result to oscillation..I have tried adjusting the Intergral to 10s, 20s then 30s but it does not help...Maybe I should turn on the derivative action?? Please help Thanks
Raffy Posts: 209 Rating: (2)
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10/9/2013 11:10 AM	Rate (1)
Marcjan Diamond Member Joined: 4/22/2010 Last visit: 3/31/2025 Posts: 5697 Rating: (716)	Hello, How and where do you call the PID block? What is the sample time of the PID and the block you call the PID in ? Perhaps a printout of the block call and a short discription of the proces could give us some more information. Regards, Marjan
	Problem solved? Please let us know! Please no technical questions by PM, use the forum sections for your questions.
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10/9/2013 4:54 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 1/5/2026 Posts: 6892 Rating: (1368)	Raffy for example when the PID adjusts and increase the position there is a delay before the power increases..I'm using PID FB41 and FB43..what should be adjusted so that this delay is compensated?? due to this delay the SP and PV would not meet and eventually result to oscillation..I have tried adjusting the Intergral to 10s, 20s then 30s but it does not help...Maybe I should turn on the derivative action?? Hello, Besides what already has been mentioned, it is interesting to know: -Sampling rate of FB43 -type of process and reaction to ON/OFF status of actuator connected to FB43 -Check if the time lag of the process is not too large (comparable with time constant of process) Best regards, Hamid Hosseini
	Last edited by: hdhosseini at: 10/9/2013 6:58 PM Demo Channel on Youtube
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10/16/2013 10:55 AM	Rate (0)
Raffy Posts: 209 Rating: (2)	Hi guys I call my PID block in OB35 and FB41 sampling time is 100MS TI is 10s and P is 1.0, I also set LMN_LLM to -100.. now my FB43 sampling time is 10MS with period time of 10s..I set it to 10s because of the delay I encounter with the system (delay in increase in power with increase in position).. But I've been trying to put the TI to 10s, 20s and 30s but It overshoots and oscillates.. P also does not work for higher values.. Please help, Thanks guys Raffy
Raffy Posts: 209 Rating: (2)
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10/16/2013 8:13 PM	Rate (1)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 1/5/2026 Posts: 6892 Rating: (1368)	Hello, If response of your system with PID controller is not satisfactory, it means that is not a suitable strategy for controlling the process. This may happen if system in not linear in the all range of operation or showing a large time lag.There are some strategies for controlling each case such as fuzzy controllers.But for a better view of your process, I suggest checking your process reaction curve(LMN in FB41 to process value). Best regards, Hamid Hosseini
	Last edited by: hdhosseini at: 10/16/2013 8:48 PM Demo Channel on Youtube
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This contribution was helpful to 1 thankful Users metwally mustafa

10/17/2013 2:49 AM	Rate (0)
Raffy Posts: 209 Rating: (2)	hdhosseini Hello, If response of your system with PID controller is not satisfactory, it means that is not a suitable strategy for controlling the process. This may happen if system in not linear in the all range of operation or showing a large time lag.There are some strategies for controlling each case such as fuzzy controllers.But for a better view of your process, I suggest checking your process reaction curve(LMN in FB41 to process value). Best regards, Hamid Hosseini Hi hamid hosseini, Correct me if I'm wrong to check for process reaction curve, I should use display the LMN in a Trend then measure the time it takes to complete a cycle or to have a value closer to the setpoint??am I right?? In my case LMN should be zero so that the FB43 would not command a negative pulse or positive pulse to the actuator..so this means when LMN is zero then the setpoint has been reached.. Is there a software in siemens or a hardware which uses fuzzy logic controllers??or Can I program it ?? Thanks for the replies, It really helped me.. best regards, raffy
Raffy Posts: 209 Rating: (2)
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10/22/2013 5:52 AM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 1/5/2026 Posts: 6892 Rating: (1368)	Hello again, Correct me if I'm wrong to check for process reaction curve, I should use display the LMN in a Trend then measure the time it takes to complete a cycle or to have a value closer to the setpoint??am I right?? Process reaction curve is somehow coming from field via transmitters.So plot the process value in your case with LMN in FB41. In my case LMN should be zero so that the FB43 would not command a negative pulse or positive pulse to the actuator..so this means when LMN is zero then the setpoint has been reached.. No command while error is zero is response of PURE P controller.If integral is existing in the scenario , most of the time you settle to steady state with some opening in the actuator. Is there a software in siemens or a hardware which uses fuzzy logic controllers??or Can I program it ?? I have heard of "Fuzzy Control ++ and Neuro System" as solution in process automation.The problem may be this products would not be supported anymore.You can search it in IT4INDUSTRY and ask help from contact data there. Also, there is possibility of wrong parameter assignment in FB43,I suggest uploading part of program related to PID regulator. Best regards, Hamid Hosseini
	Last edited by: hdhosseini at: 10/30/2013 9:15 AM //REVISE Last edited by: hdhosseini at: 10/22/2013 6:00 AM Demo Channel on Youtube
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