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PID BEHAVIOR (2)

hi matt 

thanks again,

i want to attach 2 pic so i pose new Q.

as you know  in HMI i have pid and valve and one faceplate, client wants AO/OUT has been shown on valve and FP in HMI.

ao/out is 25 % but in hmi we have 75%.....

BR.

rasa
  • Matt Stoner
    So you will need to change the FP and dynamo to use those but I would highly discourage the customer from doing this.

    The operator may not and probably doesn't know the valve fail position and select 100% on the output thinking that he/she is opening the valve in an emergency but on an increase to Close valve it would close. This would cause some big confusion so if you do this you probably need to add some other things to make sure that the operator knows what he/she is doing.

    The way it currently is, 100% is always valve fully open and 0% is always valve fully closed. I would instead suggest adding the AO/OUT on the detail display if they want to know what the value is.
  • mabboud

    In reply to Matt Stoner:

    Ashley,

    This is a common problem I have run into and your concern is that same as mine. Not only does the dynamo seem to the novice user wrong but depending on the mode of the AO block, writing a value to the SP or OUT has different results which causes all kinds of confusion.

    The SP is always in % open and if you have configured the IO_OPTS to Increase to Close, the AO1/OUT parameter is calculated as (100-SP).

    I have two suggestions:

    1. There are quite a few digital valve positioners that will allow you to invert the IP signal so 4mA (0%) = Closed and 20mA (100%) = Open even if the valve is Air to Close. The one trick with the positioner is to make sure that the wirebreak feature causes the valve to go to it's fail state (Open). The one other item to be cautious of is if the is interlock functionality incorporated into your control module, the interlock state is 100% (open)

    2. As Matt had said before modify (copy and create new) the control valve Dynamo so that instead of looking at the the AO1/OUT for the position, fill color, and % Fill, the dynamo looks at the AO1/SP. You could be creative and look at the AO1/IO_OPTS value and if the increase to close bit is set in the word, the graphics use a (100-AO1/OUT), however, this a bit more complicated. If you are going to use this method, I would highly recommend disabling Manual mode on the valve. What can happen is if someone puts the valve into manual, the valve position has nothing to do with the AO1/SP so the position on screen may not match the actual position of the valve. You can instructs operators that if they need to control the valve "manually" they can use the AUTO mode and write to the SP since the logic should be using CAS_SP for normal control.
  • rasa

    In reply to Matt Stoner:

    thank you so much

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