Karl
   It sounds suspiciously like an integrator. If this is the case then maybe
the output of the short period piezo sensor would be acceleration. I'll have to
pull the sensor out of the dust and see if it will work again.
Regards
Barry


Karl Cunningham wrote:

> Barry & Chris --
>
> Piezo devices are often used with charge amplifiers, which is just an
> op-amp with capacitive feedback and a parallel resistor to keep it from
> drifting off scale.  When the input is connected to the Piezo device (a
> capacitor) the op-amp circuit acts as an amplifier with gain of CZ/C1.  The
> low-frequency limit is given by the time constant of the resistor and C1.
> Op-amps with very low input bias and offset currents must be used.  This
> circuit provides a low-impedance output to drive other circuitry cabling,
> etc.  With some of today's op-amps having input currents in the picoamp
> range, this type of thing is quite viable.
>
> Use teflon standoffs for the connections at the inverting input of the
> op-amp.  And any cabling used between the piezo device and the circuit
> should be made with wire having insulation with very low dielectric
> absorption.
>
> Karl
>
>           +--------------\/\/\/\------------+
>           |                                 |
>           +----------------||---------------+
>           |                 C1              |
>           |             |\                  |
>           |             |  \                |
>           |             |    \              |
>           |             |      \            |
>           +-------------| -      \          |
>           |             |          \        |
>           |             |           \       |
>    Piezo ---            |            >------+------------O
>      CZ  ---            |          /
>           |             |        /
>           |       +-----| +    /
>           |       |     |    /
>           |       |     |  /
>          ---     ---    |/
>          \ /     \ /
>           V       V
>
> _


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