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DIGITAL NANOAMP METER                              1998 W. Beaty

Here's another cool thing (although I've not yet found a good use for it.)

My DVM (digital voltmeter) has a 200 microamps setting, but some sorts of
electrostatic effects deal with lots less than 1uA.  My old 20uA panel
meter is better for these, but sometimes I want to see things which barely
make it budge. I discovered a setting on my DVM meter which is 10,000
times more sensitive!  By putting the 20uA panel meter in series with the
DVM, then setting the DVM to 200mV (volts, not amps!), a small current
which sends the voltmeter to 200mV reading will move the 20uA meter
slightly.  I estimate that the 20uA meter is indicating about 1/50 of a uA
(20 nanoamps), while the voltmeter reads "200".  Aha, the voltmeter has a
10meg input impedance, so if its voltage range is instead used as a
current meter, the 200mV range is actually reading 20 nanoamps.  So if the
DVM reads 1mV, it is actually measuring 100 picoamperes!

Anyone have good ideas for applications for a digital meter with a 20nA
full scale range?  Maybe use it along with a 100v DC supply to make an
ohmmeter with a full scale range of 5 giga-ohms, then use it to measure
the resistance of wood, cloth, plastic, etc.  Maybe we could detect the
current which goes through thin glass.  Or the nano-ammeter could be used
alone to sense the air ions from a VandeGraaff machine that's on the far
side of the classroom.  Or take the meter outside, connect it to a big
sheet of foil supported by insulators, and try to detect up the
current/m^2 sky current?  Oooo, if those Radio Shack DVMs with the RS-232
outputs can do the same thing, then we could GRAPH the sky current during
the day, or watch pulses of ions drift across the classroom as the VDG was
turned on and off, etc. 

((((((((((((((((((((( ( (  (   (    (O)    )   )  ) ) )))))))))))))))))))))
William J. Beaty                                  SCIENCE HOBBYIST website
billbeskimo.com                                  amasci.com
EE/programmer/sci-exhibits          science projects, tesla, weird science
Seattle, WA   206-781-3320          freenrg-L taoshum-L vortex-L webhead-L