Circuit for computing frequency of piezoelectric crystal

Discussion in 'General Electronics Chat' started by superhugefatass, Oct 11, 2010.

  1. superhugefatass

    Thread Starter New Member

    Oct 11, 2010
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    Let me preface by saying that I have only a vague knowledge of electronics. I want to build a simple transducer of pressure by which an expanding substance presses against a piezoelectric crystal, altering its frequency. Can anyone point me to an IC or circuit design for measurement and output of frequency?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    They make transducers off the shelf for what you want. I suspect doing what you want will only kill the oscillation, not alter the frequency. Try putting you finger on a piece of crystal that is ringing.

    http://www.mcmaster.com/#pressure-sensors/=98h7iy
     
  3. someonesdad

    Senior Member

    Jul 7, 2009
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    If you insist on building your own, it wouldn't hurt to first get an education about what technologies are already used to convert pressure to an electrical signal. Hit the library for books on instrumentation.

    It would be quite unlikely that you would be able to design anything better than the plethora of sensors that already exist (not to mention that your development costs will probably be much more than such sensors cost).

    You didn't give any indication of the range of pressures you need to measure nor the required accuracy, but you may be able to find some good deals on ebay. I found some surplus 0-1000 psia sensors that were used in military aircraft that are quite heavy duty and work well. They cost me about $13 apiece delivered. I believe they cost the government more than $1000 each when new.
     
  4. superhugefatass

    Thread Starter New Member

    Oct 11, 2010
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    Bill and someonesdad,

    In truth, I am unsure of what the pressure might be; I only know that it will likely be in the microbar to millibar range. I will look more closely at pressure transducers available. One used for a very sensitive balance may work for a proof of principle.

    I only know that if something is measured in whole number PSI, it will likely be too unresponsive for my purposes. I am trying to build a biosensor. If push comes to shove, I can use an optical cantilever to register pressure, but that will make the device I am trying to build too costly.

    Where should one look commercially for transducers of extremely small pressures?
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Sounds about right to me. Never had to find one, but they have to exist. Think something that measures barometric pressure (which sounds like what you are trying to do). If it is a pretty tight vacuum I used to see a thermocouple pressure gauge for measuring near vacuum conditions (sounds like a contradiction, doesn't it?).
     
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