Piezoelectric Sensor question

Discussion in 'General Electronics Chat' started by hazim, May 24, 2010.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Hello,

    My friend is building a project which has several piezoelectric sensors used as pressure sensors. These sensors are connected to a summing amplifier, the signal is to be amplified and rectified/smoothed in order to be the changed input of a comparator..
    When the pressure exceeds a certain limit, the comparator output becomes HIGH.

    The smoothing capacitor should be selected according to the frequency of the signal, but don't know what would be the frequency, and I read that it varies as the voltage varies... so I'm a little confused what to do with that. I built a primary circuit, and tried it on Multisim (attachments).

    Any idea is appreciated.
    Regards,
    Hazim

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  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If the intent is to sense some increase in pressure up to a set limit, then piezo sensors are not a good choice. They have outputs only while the force on them is changing. The output is also larger when the rate of change is high.

    Is the intent to sense pressure or applied force?
     
  3. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Pressure. What other sensors will work? Strain gauges aren't available here in Lebanon..
     
  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    I remember seeing a device usng a bit of the black anti-static foam between two pieces of metal foil as a mechanical pressure sensor.

    The resistance is supposed to be proportional to the pressure applied.

    I think the problem with that may be finding some none-brittle anti-static foam, all the stuff I've seen resently is hard rather than springy.

    Something like anti-static bubble wrap may work?
     
  5. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    I want a pressure sensor.. as a part in the circuit. You mean that nylon cover with air bubbles..? how could it help?

    The sensor will be placed on something like a balloon filled with water. The circuit will detect when the pressure exceeds a certain limit..
     
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Using something flexible, compressible but conductive and fairly high resistance between two foil or metal plates should give you a 'cell' whos resistance varies with pressure.

    I have seen conductive foam used, conductive bubble wrap should give a similar effect though each bubble is larger. (I'm thinking of the transparent pink stuff).

    It's down to what materials you have available.
     
    hazim likes this.
  7. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
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