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differential charge amplifier

Discussion in 'General Electronics Discussion' started by Alektheanswer, Mar 25, 2016.

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  1. Alektheanswer


    Mar 25, 2016
    Hi everyone,
    I'm trying to design a vibration sensor (1-1000Hz). I got an electrode, a foam layer and a mettalic fabric (the stack form a capacitor). When a vibration appears, it moves the charges inside the capacitor and change the capacitance value.
    My capacitor needs to be polarised if I want that the charges move when there is vibration.
    My basic schématic is Dynamic.png
    I would like to measure it with différential measurement like :
    My problem is contrary to the piezo module, my capacitor need to be polarised so I can't have the same potential with my capacitor terminals.

    Do you have any ideas?

    Thank you
  2. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Try lifting the common ground connection to the two Rs resistors and applying positive and negative bias voltages.

    Not sure why you would want differential connections to your capacitance transducer, since it does not appear from your description to have a balanced output. Just ground your electrode, take the signal from the metallic fabric, and apply it to the current-to-voltage amplifier in your first circuit.

    The capacitance in the connecting cable, as well as triboelectric effects, will be a problem unless you can isolate the cable from movement and vibrations. There is a special coaxial cable available (normally used with piezo-electric transducers) that has a conductive graphite paste between the outer shield and the insulator of the inner coaxial conductor that will help to control spurious output from cable flexure. Unfortunately, this special coaxial cable is a real bitch-kitty to work with because it is easy for the graphite to "short out" the signal when the cable is assembled to a connector, usually a Microdot connector.

    Can you provide us with a clue as to what you are trying to DO with this custom foam-backed fabric with metallic electrode?
    Arouse1973 likes this.
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