>>With a sensitive instrumentation amp you can measure the voltage
>difference >between your feet and your head (usually a couple hundred volts
>over six feet).
>
>This is really interesting!
>
>But if it's a couple of hundred volts, why do you need a sensitive
>instrument amp?
>
>Bruce

Actually, it's not that it has to be all that sensitive, but high impedance
and high CMRR is a must. Basically you are building an electrometer. Then
there's the trouble with static buildup. Without something like the
radioactive sources mentioned previously in this thread to dissipate charge
buildup, the sensor would quickly saturate and become unresponsive to
changes in the voltage potential in the environment.

I wonder, though, whether you could get around the need for radioactive
sources by periodically shorting your sense and reference plates together.
Anybody out there know?

--BN



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