Rockwell – CASCADE PIDE CONTROL

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  • #20785
    khyap96khyap96
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    Hi all,

    For my project, I need to control a flow control valve (FCV). Where a pressure transmitter is located before FCV to check pressure and a flow transmitter is located after FCV to check flow rate. You may refer attachment for clearer image.

    I believe this is a cascade control where,

    1. Pressure is first checked. If pressure ? 8.5 barg, the FCV is controlled by pressure. If pressure ? 8.0 barg, FCV will be totally closed. (Pressure setpoint at 8.5 barg)
    2. Else, it is controlled by flow. (Flow setpoint at 140Sm3/h)

    I have started a draft of the Cascade PIDE, as attached. But I think something is wrong because it fails when I try to simulate using Logix Emulate. Can anyone please advise or help?

     

    Regards,

    Sally

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    #20788
    tdamonThomas Damon
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    That is not a case for PIDE cascade control, you would use cascade control if the output of the first PIDE is the setpoint for the next.  You need 2 seperate PIDE’s with a low select going to the valve.

    #20791
    khyap96khyap96
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    Karma: 16
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    Hello Thomas,

    Thank you for your advise! Did you mean this should be a multiloop control, scheme on page 7 as attached in pdf file?

    Also i have attached a draft of a multiloop PIDE.

     

     

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    #20796
    tdamonThomas Damon
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    Yes, the 2 loops interact as per page 7 with it set for low select.  Make sure to bring the output of the select block back to the CV Previous of both PIDE’s so the non- controlling one stays active and doesn’t windup.

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