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DeltaV - MPC: Question mark at the output of the MPC block.

Hello guys,

First of all I am sorry if my question is something very basic and I'm just wasting your time, but I tried to solve the issue and until now I got no positive results. I am trying to use the DeltaV model predictive control (MPC block) to control some parameters of a evaporator plant for my undergraduate thesis and the initial goal is to control the voltage value applied to a motor based on a level value; however, I always get an yellow circle with a question mark in it at the output. The control is working flawlessly when I use a PID control though. 

Thank you very much for your help!

Pedro.

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EDIT 1: Thank you very much for all the support, I'm sorry for the long time I took to answer but this week has been very busy. Anyway, I am attaching two images, the first one shows how I was connecting the MPC block, the interrogation mark was showing up over the MNPLT1 output. I read about it and it could mean that that output was OOS. As I couldn't figure out how to solve the problem, I decided to connect the MPC block directly to the main panel in which I have all the inputs and outputs as shown in the second picture below to see if it would work properly. Apparently, the problem was solved, but I still would like to use a separate module like the one shown in the first picture. Too clarify, the LT001 represents a level sensor and the SC001 represents the signal that goes to the frequency inverter responsible for the pump.

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EDIT 2: Hello guys, as I said in the last edit, the MPC block seemed to work fine when inserted in the same module as the inputs and outputs (Attempt #2). However, when I tried to use it as the input to a PID controller, I got a problem similar to the initial one described on the main post, a yellow question mark at the BKCAL_OUT of the PID block. Both the MPC and the PID seemed to work just fine when working alone, but I can't get them to work together. Another problem is that the PID keeps changing the actual mode to MANUAL although it is configured to CASCADE.

Again, thank you very much.

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EDIT 3: Yellow question mark problem was solved; however, MNLPT and BKCAL_IN values of the MPC block equal to zero.

Attempt #1: DIDN'T WORK - Yellow question mark over the MNPLT

Attempt #2: IT WORKED

Attempt #3: DIDN'T WORK - Yellow question mark over the BKCAL_OUT in the PID block.

Attempt #4: DIDN'T WORK - MNPLT and BKCAL_IN of the MPC block equal to zero

MPC Operate: 

Pedro Torreao
  • fairchdm
    Pedro,
     
    Your problem could be from several different issues.
     
    Could you add an image of your logic?
     
    The way you connect your points between function blocks, the number of inputs, the number of outputs you are trying to control, etc.
    Any module or block diagnostic alarms?
    We will need more detail to provide any assistance.
     
    Regards,
     
    Dennis Fairchild
    ICE Lead
    McClain Power Plant
     
     
     
  • James Beall
    Pedro,
    Since you are using the MPC (not MPCPro or MPCPlus) block, have you wired the MPC block output (MV) to the CAS or RCAS of an AO block. Have you opened the MPC block with Predict and either tested to determine the model or typed in the process model if you know it? If you use the testing routine, be sure to set the time to steady state (an integer multiple of 120 seconds, minimum 120 seconds) before running the test. Books On Line has a good explanation of this procedure. If you need more information, I could send you one of my presentations on the topic.
    James
  • James Beall

    In reply to James Beall:

    One more thing, if you only have one MV/CV, you need to reduce the size of the default MPC block. To do this, right click on the MPC block, select "Extensible parameters" and change the number of MV's to 1.
  • James Beall

    In reply to fairchdm:

    As Dennis says, a screen shot of the Module in Control Studio Online, and of the MPC Operate /Status display would be very helpful.
  • Pedro Torreao

    In reply to James Beall:

    If you don't mind, I would be very grateful.
  • Pedro Torreao

    In reply to James Beall:

    I did that, but thank you for the information!
  • Pedro Torreao

    In reply to fairchdm:

    I edited the original post and added two pictures, I hope they help to clarify my doubts.
  • James Beall
    The #1 application has a configuration problem. You must wire the MPC MV output directly to the input of the block to be manipulated. If this is not possible, you can use an MPC OUTREF composite block from the Advanced Control pallete to make a remote connection.
    The #2 application looks ok on configuration.

    It would be helpful to see a screen shot of the MPC Operate (DeltaV operator programs, browse to module/MPC1). Click on status and send a screenshot of the status.
    When I get to my computer, I’ll send you my presentation on the topic.
    James
  • fairchdm

    In reply to James Beall:

    Pedro,
    I agree with James about having a screen shot of your MPC Operate screen to see your status.

    Typically, I like to keep the modules as simple as possible. (e.g. One AI, MPC, One AO).
    Also, in #2 the MPC block sequence number needs to be before the AO block.

    Regards,
    Dennis
  • Lou Heavner
    Are you using Foundation Fieldbus I/O? If so, are you writing to RCAS_IN or ROUT_IN? If so, I don't think that will work. We often use the convention of writing to the RCAS_IN of MVs. But if you are writing to a FF device, the RCAS_OUT is request-response instead of unsolicited and will not update as required by the MPC block. I only mention this because it looks like your inputs are FFAI's which I assume may be Foundation Fieldbus inputs.
  • Pedro Torreao

    In reply to James Beall:

    Hello, I edited the post to include the changes made and I added the screenshot that was asked. Thank you!
  • Pedro Torreao

    In reply to Lou Heavner:

    I will check that, thank you very much!
  • Pedro Torreao

    In reply to fairchdm:

    Hello, it may not be on the picture that I just added, but I did the modification that you suggested in the block sequence, thank you!
  • James Beall

    In reply to Pedro Torreao:

    You have to wire to the input and output blocks inside the same module OR use the MPC_INREF and MPC_OUTREF blocks from the advanced control palette to connect to appropriate function blocks in other module. Also, it appears that you changed a scale or connected to a block with a different scale which triggers one of the messages you are getting.

    I have a presentation on this topic, send an email to me at james.beall@emerson.com and I will send it to you.
  • James Beall

    In reply to James Beall:

    I figured out how to attach my presentation!  See attached.  Let me know if it comes through with sufficient resolution.

    James

    6-14908 - Caldwell_Beall _FINAL.pdf

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