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Strain Gage Seismometer

Discussion in 'Electronic Design' started by gmv, Sep 30, 2003.

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  1. gmv

    gmv Guest


    Does anyone know a good source for strain gages ?

    I just want a strain gage and not the electronics
    everyone tries to sell with it.

    I checked Google and could find only one supplier
    and the prices were all too high.

    I am experimenting with the idea of using a strain gage
    as a seismic sensor and need a cheap source of parts.
    Used parts are A-OK.

    I figure you might be able to simply support a mass
    upon a strain gage somehow then extract the signal
    down to the noise grass then look for seismic signals.

    Any ideas here are welcome.
  2. John Hall

    John Hall Guest

    I think the PIR (passive Infra-red) sensors used to detect motion for
    switching lights on are basically piezo-electric plastics, so should
    respond to mechanical strain. Of course they are also sensitive to
    heat, so you may need to allow for that also.
    You do get some electronics with them when packaged as people-sensors,
    but for a one-off project that may be cheap enough to discard.
  3. Active8

    Active8 Guest

    there was a piezo speaker element with a brass disk at one time. you can
    solder the opposite edges of the disk to copper clad PCB. the top PCB
    can be as long as needed (eh, just add an arm to it) to act as a moment
    arm which will amplify the vibrations. the piezo element could then be
    connected as one element of a wheatstone bridge no... that's how you
    connect a strain gauge... just use a low noise opamp, maybe a
    differential/instrumentation amp.

    note: according to the EE bible, these "dynamic acceleration
    transducers" don't respond appreciably to acceleration fluctuating at a
    rate of less than 5Hz because motion is restrained by the crystal.

    acceleration transducers are made with a seismic mass restrained by a
    spring and damped. a magnet in the mass with a coil pickup would provide
    output. these work down to "essentially" 0Hz.

    IIRC you should get a return from google on this and someone supplied a
    company or link with a transducer that might work for you.

  4. gmv

    gmv Guest

    An IR motion detector/Piezo thingy will not fill the billet.
    It must be passively resistive in nature and reqire
    something like a bridge circuit to function.
  5. Rob

    Rob Guest

    I assume you are in the US somewhere. Radiospares / RS Components sell
    individual strain gauge sensors (foils) for about Aust$6 (US$3 ?) each. RS
    also used to sell a small flexure sensor, I think it was piezo based. It was
    like a small ruler from memory 3 or 4 cm long and a couple wide. IIRC it had
    a reasonable output for a small displacement. Suspend it from one end, stick
    a small weight on the other and you might have a seismometer sensor.
    I am sure there are a heap of companies you could source plain strain gauges
    Have a look at:

    Good luck.
  6. Leon Heller

    Leon Heller Guest

    Have a look at the ADXL202 accelerometer and similar devices from ADI.

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