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PID fb41 auto to manual mode

Created by: JanLan at: 11/7/2011 2:49 PM (1 Replies)

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11/7/2011 2:49 PM	Rate (0)
JanLan Advanced Member Joined: 10/8/2008 Last visit: 11/5/2024 Posts: 43 Rating: (0)	Hi All, For my project I use the FB670 this is the faceplate for a FB41 control loop the faceplate is used in WinCC v7.2. In my project for example I read in a sensor with a range from 0 - 1200 degrees. It is possible to move this signal direct to the FB41 using the PV_PER input.I use the PV-Fac to scale the signal to the faceplate PV_FAC = 12. The output is limited from 0 - 100 %. to acief this I use the factor LMN_FAC = 0.0833 (1/12). All the values are now correct displayed in the faceplate.However when you change from auto to manual (see item bumpless FB41) the manual is first the last output value, but after the next scan OB X = 1 sec. the manual value is devided by the LMN_FAC. can someone give me an example where scaling is used, and this auto manual problem is solved. What is wrong in the control when I see that the LMN output is in the range 0- 100 but the LMN_P, LMN_I and LMN_D outputs accumulated are more than the LMN_Output (100%) LMN_HLM = 100%

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11/7/2011 10:35 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 10/26/2024 Posts: 6852 Rating: (1365)	JanLan For my project I use the FB670 this is the faceplate for a FB41 control loop the faceplate is used in WinCC v7.2. In my project for example I read in a sensor with a range from 0 - 1200 degrees. It is possible to move this signal direct to the FB41 using the PV_PER input.I use the PV-Fac to scale the signal to the faceplate PV_FAC = 12. The output is limited from 0 - 100 %. to acief this I use the factor LMN_FAC = 0.0833 (1/12). All the values are now correct displayed in the faceplate.However when you change from auto to manual (see item bumpless FB41) the manual is first the last output value, but after the next scan OB X = 1 sec. the manual value is devided by the LMN_FAC. can someone give me an example where scaling is used, and this auto manual problem is solved. What is wrong in the control when I see that the LMN output is in the range 0- 100 but the LMN_P, LMN_I and LMN_D outputs accumulated are more than the LMN_Output (100%) LMN_HLM = 100% Dear JanLan, I believe online manual provided in STEP 7 on FB41 will answer to all your questions here.Diagrams and formulas will help you to understand the whole algorithm and relation between each section easily .I upload the "pdf" version of the online help for quick reference . JanLan The output is limited from 0 - 100 %. to acief this I use the factor LMN_FAC = 0.0833 (1/12). As you follow the diagrams and formula in the attachment, output of LMN limiter block is determined by high and low limit there (e.g 0 to 100) and by LMN_NORM block , you can create linear transform of the input.For example, in some case you need to change (0 to 100) of normal PID algorithm to 100 to 0(LMN = (output of LMNLIMIT) * LMN_FAC + LMN_OFF). JanLan can someone give me an example where scaling is used, Check some examples here:Standard PID Package - FB41 Samples (hd_FB41_EX.zip ) JanLan and this auto manual problem is solved. For this issue ,"Bumpless PID" would be a great help on bumpless implementation of algorithm.Also check here to see here "Why is manual to automatic changeover in FB58 bumpless?". JanLan What is wrong in the control when I see that the LMN output is in the range 0- 100 but the LMN_P, LMN_I and LMN_D outputs accumulated are more than the LMN_Output (100%) LMN_HLM = 100% For more academics details on PID controller refer to THIS which is great reference to understand the behavior of algorithm. Chapter 3 (PID control) of this book is a great help to understand the issue and eventually design your own controller! Best regards, Hamid Hosseini Attachment FB41.pdf (710 Downloads)
	Demo Channel on Youtube
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