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Thread: Why isn't my VO defering?

  1. #1
    NSI Member Krazie4Acans's Avatar
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    Why isn't my VO defering?

    Can anyone explain why my VO is not deferring like my code is telling it to? I have a DC return that has a soft start on it and so I need it to have time to come to full speed before it reacts to the flow sensor condition. What am I doing wrong?

    Fallback OFF
    Set OFF
    If FLRTN8 < 500 Then ON
    If Output Rtn_Pmp_5_6 = OFF Then OFF
    If FeedA 000 Then OFF
    If FeedB 000 Then OFF
    If FeedC 000 Then OFF
    If FeedD 000 Then OFF
    Defer 005:00 Then ON

  2. #2
    Frequent Visitor Todd's Avatar
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    How exactly is it behaving? Is it changing to ON immediately or not at all?

  3. #3
    NSI Member Krazie4Acans's Avatar
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    It is cycling on for ~30 seconds then off, then on and then off. If I turn it off manually then the pump comes up to speed and I can set the VO back to auto and it will run just fine. so it's only happening during a startup from the pump being off.

  4. #4
    Frequent Visitor Todd's Avatar
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    Are you using this VO to also control the Pump outlet? If so, that's no good. You get in a kind of feedback loop where each outlet is trying to control the other.

  5. #5
    NSI Member Krazie4Acans's Avatar
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    This is the code from my return output:


    Fallback ON
    Set ON
    If Output Rtn_Bad_A9 = ON Then OFF (this is the VO that I posted the code for in the OP)

  6. #6
    Frequent Visitor Todd's Avatar
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    Yup, feedback loop. Take the If Output Rtn_Pump_5_6 line out of the VO. This is preventing the pump from ever coming up to speed.

    To be honest, it doesnt look like the VO is necessary. Move the sensor line, feed lines, and defer to the return pump outlet and remove reference to the vo.

  7. #7
    NSI Member Krazie4Acans's Avatar
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    The If Output Rtn_Pump_5_6 line can't prevent the pump from coming on as there is no time on it and it is on if the pump is spinning up.

    I need the If Output Rtn_Pump_5_6 line in there so that the VO doesn't turn on when the pump is off and prevent the pump from coming back on at the end of a feed cycle.

    I have many other functions that are coded around this VO so removing it isn't an easy task. The other stuff is working great and if the defer was working on this VO everything would be happy.

  8. #8
    Frequent Visitor Todd's Avatar
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    You wouldn't think so, but funny things happen when you have two outlets trying to control each other at the same time. Also, it is a good idea not to overly alter the behavior of a sensor. Instead, alter the response of the outlets that rely on the sensor. Can you try removing the Rtn_Pmp_5_6 line temporarily and see if it works?

  9. #9
    NSI Member Krazie4Acans's Avatar
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    Are you saying that some how the apex is deciding to turn the VO on even though none of it's conditions are being met when it's processed?

    So if the VO is evaluated before the return pump:
    Pump is on (as it's spinning up), flow is less than 500 but the on should defer that for 5 minutes and so it shouldn't turn on. The spin up take less than a minute to get to greater than 500 so there is ample time for it to stabilize before the deferred on would become active.

    If the Return pump is evaluated prior to the VO:
    Return pump is on (it's spinning up), VO is off (deferred 5 minutes), Pump spins up to full speed.

    Are you saying there is a race condition where the VO could be seeing the Return outlet as off even though the pump is spinning up?

  10. #10
    Frequent Visitor Todd's Avatar
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    Quote Originally Posted by Krazie4Acans View Post
    Are you saying there is a race condition where the VO could be seeing the Return outlet as off even though the pump is spinning up?
    Yes, that is the term I was failing at. I just know from past experience it is bad practice to have two outlets controlling each other.

  11. #11
    NSI Member Krazie4Acans's Avatar
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    That is going to suck if that's the case. Maybe I'll have to change the logic for the VO to use a second VO to get rid of the direct reference to each other.

  12. #12
    Frequent Visitor Todd's Avatar
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    I don't think using another VO will help. It is still circular. I'm trying to understand why you need the Rtn_Pmp_5_6 check in the VO. If you are using this for other outlets, do the pump check there.

  13. #13
    Frequent Contributor zombie's Avatar
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    You need this to acheive what you want. Use a min time and/or when statement to set the cycle time or lock out the pump so it doesn't short cycle at low flow. XXX is the amount of time you want it off before retrying.


    Fallback OFF
    Set OFF
    If FLRTN8 < 500 Then ON
    If Output Rtn_Pmp_5_6 = OFF Then OFF
    Defer 005:00 Then ON
    Min Time XXX:XX Then ON

    Or

    Fallback OFF
    Set OFF
    If FLRTN8 < 500 Then ON
    If Output Rtn_Pmp_5_6 = OFF Then OFF
    Defer 005:00 Then ON
    Min Time 000:05 Then ON
    When On > 000:04 Then OFF





    You might be an engineer if...You have no life and can prove it mathematically.

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