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Building a vibration sensor

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by mmilbury, Jul 5, 2002.

  1. mmilbury

    mmilbury New Member

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    I'm building an acceleration sensor for a project with low g's. (.05<g<1.0 max g = 2.0) I've researched several sensors on the web and have selected a sensor with a sensitivity of 120 pV/g.

    My understanding is there is a known mass that reacts to the vibration. This reaction is output as a certain voltage. What I am attempting to do is interface my accelerometer with a circuit board.

    Would anybody know how I would do this? I would like to make a direct connection to the ADC without using an amplifier circuit. With this in mind, what would be the best way to do this? If I go as high as 2.0g's would you know how I could limit this voltage to keep it from overloading the processor?

    Any help would be greatly appreciated.
     
  2. Argonheart

    Argonheart New Member

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    Stockholm Sweden
    Hi,
    just checking I understood right, since I've not been working with
    acceleration sensors before.

    Is the voltage output from a sensor really as low as 120 pV / g,
    so at 2g you will only get 240 pV output ?
    If that is correct, its quite small voltages you have to work with.
    Even an 18 bit A/D converter has a resolution of about 1uV / LSB
    and you would need something like 100.000 - 1000.000 times better resolution than that to get any data from your sensor.

    It looks like a very good amplifier is needed between the sensor and the A/D converter.

    Aren't there units with sensor and amplifier integrated that you could use ? They should have much higher output voltages, and their output could probably be fed stright into an A/D converter,
    maybe amplified by a very simple amplifier first.

    /Argonheart
     
  3. mechie

    mechie New Member

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    Location:
    Lincolnshire, England
    Piezo-electric accelerometers

    Mmilbury,
    I believe there could be a mis-quote in your posting -- piezo-electric accelerometers produce Coulombs of charge as their output, not volts.
    A typical industrial accelerometer will produce 25pC/g so if you meant charge, your 120pC/g unit is a massive output :shock:

    One Coulomb is one amp.second [NOTE that is multiplying NOT dividing]
    One amp is one Coulomb/second [This is dividing !]

    Because of the extremely small energy levels involved, these devices are connected with 'charge cable' - a good quality sceened cable - to a 'charge amplifier' which produces around 100mV/g (fancy name, simple circuit!). Could this be what you meant? 120mV/g ?

    It is impossible to connect directly from accelerometer to A/D, you must use a charge amp -- accelerometers are available (for a price!) that contain the charge amp and so give mV/g directly, but then they require power, usually over the same two wires as the signal, so some DC offset is involved (possibly 12 to 24v DC).
     
  4. dave

    Dave New Member

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  5. gabriella78

    gabriella78 New Member

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    Hi I just would like to know what did u do at the en with your vibration sensor.I have to do a project about it and I was wondering if u could help me out...
    Gabriella :D
     

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