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  1. #1
    Join Date
    Jun 2005
    Location
    Ohio
    Posts
    1,720

    MP580/581 TGP Question

    Why would anyone multiply both the set point and controlled variable input (separately) by 100, then bring them into a PID? This was for building static pressure control.
    You CAN choose the decimal places for both values.
    Is it an internal PID resolution issue?
    jogas

  2. #2
    Join Date
    Nov 2004
    Location
    Practically Canadian ehh.
    Posts
    675
    Decimal place limitations.

  3. #3
    Join Date
    Jan 2003
    Location
    USA
    Posts
    1,763
    I do it all the time. Decimal points are so much the problem with 32bit floats. I either have to use massive gains & integrals or just multiply the inputs and use normal P & I gains for good control.

    ie if set point is 0.02 and the input is 0.015 the PID needs some large gains, otherwise an error of 0.005 won't cause it to do anything. Now if the same PID sees 20 as the set point and the input is 15, error of 5, the gains can be "normal values" and I'll get a good control.

  4. #4
    Join Date
    Jun 2005
    Location
    Ohio
    Posts
    1,720
    Gentlemen, Thank you.
    jogas

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