Pi filter applicable?

Discussion in 'The Projects Forum' started by DunnoSquat, May 17, 2011.

  1. DunnoSquat

    Thread Starter New Member

    May 17, 2011
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    Assume:
    I am a moron

    Given:
    I have a 12V AC to DC inverter exciting a transducer. I have a lot of noise on the output. Will this type of filter help me out? If so, how do I choose the capicitance and inductance values? If not, what type of filter would be best?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    282
    We probably need more information. Inverters, for instance, make DC into AC. Rectifier circuits turn AC into DC, and then you can add a regulator to produce high quality DC (noise free).

    What does your circuit look like and what is the nature of the noise?
     
  3. DunnoSquat

    Thread Starter New Member

    May 17, 2011
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    I have an Enercell AC to DC power adapter that plugs into the wall, power going to the excitation on the transducer, ground to ground. Output of transducer to DAQ device. Reading with Labview. There is a swing of around 200 psi on my graph looks pretty choppy. When I hook up batteries instead of the power supply its golden. If I can get the power supply to look like the batteries that would be great. Possible?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Can't say much without knowing what's in it. What voltage does it put out?
     
  5. #12

    Expert

    Nov 30, 2010
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    Just put a nice, fat, capacitor on the output of the wall wart and see what happens. Maybe 1000 microfarads at 25 volts.

    This is pure guessing, but it's guessing by somebody with 40 years of experience.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    It might be a switching supply; if so, a large cap might not get rid of the high frequency components. A coupled inductor with a cap on the input and output should take care of it.
     
  7. DunnoSquat

    Thread Starter New Member

    May 17, 2011
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    How do I choose the correct valued inductor and capacitor?
     
  8. #12

    Expert

    Nov 30, 2010
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    Considering that you haven't told us what frequency or amplitude you have to filter out, or how clean you need it, we don't know.
     
  9. DunnoSquat

    Thread Starter New Member

    May 17, 2011
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    0
    Remember my assumption above.
    Im sampling at 1000 hz. The noise looks like 500 hz?
    The reading oscillates +/- .2 mA which relates to around +/- 200 psi. With the batterys I have a flat line, no oscilation. This is what I would like to get to with the power adapter.
     
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