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Input pressure required to produce controller output values

  1. Mar 8, 2016 #1
    1. The problem statement, all variables and given/known data

    A direct acting proportional pressure controller has a gain of 3, a range of 0-40 bar and is set to control at 25 bar. When the measured value and the desired value are equal, the output signal is 60%. Determine the input pressure required to produce controller output values of 10% and 90%

    2. Relevant equations
    Gain = 100 / % proportional band setting

    3. The attempt at a solution
     
    Last edited: Mar 8, 2016
  2. jcsd
  3. Mar 8, 2016 #2

    BvU

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    Ho oxon,

    So far I have read 1. How about providing 2 and 3 as well ? -- if only to avoid being shot into the black hole ...
     
  4. Mar 8, 2016 #3
    1. The problem statement, all variables and given/known data

    A direct acting proportional pressure controller has a gain of 3, a range of 0-40 bar and is set to control at 25 bar. When the measured value and the desired value are equal, the output signal is 60%. Determine the input pressure required to produce controller output values of 10% and 90%

    2. Relevant equations
    Gain = 100 / % proportional band setting
    PB = 100/gain

    3. The attempt at a solution

    PB = 100/3 = 33.33%

    33% of input scale (0-40 bar) = 13.33 bar

    not sure where to go with this now...
     
  5. Mar 9, 2016 #4
    ok here is what i got...




    33.33% of input scale (0 - 40 bar) is 13.33 bar


    60% of 13.33 bar = 8 bar

    50% of 13.33 bar = 6.67 bar

    40% of 13.33 bar = 5.332 bar

    30% of 13.33 bar = 4 bar


    0% Output = 25 - 8 = 17 bar

    10% Output = 25 – 6.67 = 18.3 bar

    90% Output = 25 + 4 = 29 bar

    100% Output = 25 + 5.332 = 30.3 bar
     
  6. Mar 9, 2016 #5

    BvU

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    Could it be that the recipe for your proportional controller is as follows (consult your notes or textbook - I'm just guessing)
    • set point is subtracted
    • result is converted to %
    • gain is applied
    • offset is applied
    Example: 25 Bar in. 25 bar is subtracted. 0 Bar is 0% 0% is multiplied by 3 add offset 62.5% to get result
    Example: 27 Bar in. You see what comes out. Now express the recipe in a formula.
     
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