potential sensor (copier)

How tiny? We used to build field mills as small as four inch diameter for experiments but the ones deployed outdoors were always the big, rugged, 10 inch diameter variety. Do you have machine shop access? Field mill mechanical construction is straight-forward and well documented.

Regards,

Michael

Whats wrong with a floating gate FET like used in small microphones? They are cheap enough to cannibalize one, and even the circuit behind such a microphone can be copied to read the voltages on the drum. The Fets are small, and you can use a few millimeters gatewire as a sense electrode. Put the rest of the Fet in a grounded shield, with only the gate wire poking outside. And the smaller the hole the wire is peeking through, the smaller the sense area becomes, altough the sensitivity will then be much smaller. Keep us posted.

A general reference for the casual reader of this thread of an overview of electric field measuring techniques may be read here:

This is by no means comprehensive but it is a useful description of some common techniques.

We also used to build radioactive probes (also described in the above document) which is a cheap alternative; look to ionization smoke detectors for the sources ;-)

Regards,

Michael

we have a couple of the floating fet ones, but the boss wants better and distance insensitive, so we need the rotary chopper type. I found a surplus one out of a electrostatic coater,and got it working, but its housing is too big. My target is a electrospun nanofiber jet, and the whole assembly is only 6" from top to bottom, so I need a very tiny probe. Since the fiber is made electrostaticly and in cross section looks like the Tasmanian Devil from Bugs Bunny Cartoons, I need a meter that measures independant of target size and location. The rotary chopper or tuning fork ones will do that. I dont want to measure voltage on a surface, I want to see the space charge field in volts per meter. Plus it would be nice to have a off the shelf unit so each grad student could have their own. Commercial instrument grade ones are too big.

Thanks, Steve

Thanks for the paper, very interesting. Whats the geometry of the RA probe? That looks promising and I dont mind hacking the smoke detector sources. The campus rad safety officer's gonna have nightmares, but he can be delt with. We have a world class machinist, fabrication is not a problem. If I could shrink it to pager motor size,. it would be wonderful.

Thanks, Steve