Re: vibrating capacitor Electrometer design (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 12 Jul 2004 12:53:12 +0300
From: Kristian Ukkonen <kristian.ukkonen@xxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: vibrating capacitor Electrometer design (fwd)


High Voltage list wrote:
> Original poster: Steven Roys <sroys@xxxxxxxx>
> From: David Dameron <ddameron@xxxxxxxxxxxxx>
> If you bought the Amateur Scientist CD set, please look at the Oct. 1965
> issue. Here a capacitor was made with a vibrating plate, so any charge is
> converted to an AC voltage, by q = CV, where C varies with time.
> At 08:10 PM 7/10/04 -0600, you wrote:
>>	I haven't looked at those links yet (will do, of course), but before I
>>do I have a couple of questions someone here may be able to answer.
>>1.  How about vibrating reed electrometers?  Anybody know anything about
>>them.  Seems to me a very easy and cheap vibrating "reed" could be made
>>with a small loudspeaker.
>>2. Has anyone looked into using varicaps or the like?

In electrochemistry there is a method for making potential
distribution maps of surfaces, by having a quite thin
piece of wire attached to a loudspeaker, with the end
of the wire near the surface, and measuring the AC current
to wire with phase sensitive detector - at the frequency
that the loudspeaker voice coil is driven, and then having
an integrator (I controller) to control the potential of
the piece of wire so that the AC current is minimized - ie.
potential of wire and surface are equal when there is no
AC current.

This is, IN EFFECT, a vibrating capasitor setup with the
capasitance between end of wire and the furface, with
the capasitance changing when the distance between
end of wire and surface being changed by voice-coil
movement of loudspeaker.

Best regards,

   Kristian Ukkonen.