----- Original Message ----- From: "Horace Heffner" <[EMAIL PROTECTED]> Sent: Tuesday, June 26, 2007 7:04 PM ... >> But anyway the slit plate experiment is better, it doesn't count on >> the "ground around" and it works in steady state. >> >> It's quite easy to measure a small DC current BTW, all you need is >> a current to voltage amplifier which will let you measure tiny >> currents to a virtual ground without an intervening resistor >> (budget deflates ;-), see http://hyperphysics.phy-astr.gsu.edu/ >> hbase/electronic/opampvar2.html >> >> It can be made inexpensively using a cheap FET input (near infinite >> impedance) op amp such as the TL071. Use e.g. a 1 Meg resistor for >> feedback, so you'll get -1mV per entering nA. You can protect the >> virtual ground input against arcing by clamping it to actual ground >> with two antiparallel diodes. > > > This is a nifty approach. I like it. It's similar to using a > voltmeter as a nano-ammeter. Have you done this?
I haven't but I think I see what you mean, it's quite ingenious. Knowing the voltmeter's input impedance say 1 Meg too, it should read 1mV for each nA you feed its voltage input terminal. It's not arcing-proof and the voltage is offset from ground by Ohm's law ---which is not a problem when source voltage is high and/or the current is quite low--- but you can't beat it in terms of simplicity :-) The I to V amplifier circuit can be pushed to better sensitivities than the nA of course, that's the approach used in those fancy expensive electrometers able to measure femtoAmps, only they use higher end op amps than the TL071, e.g. the AD549. > The big problem, though, is still who wants to do the overall > experiment. I suggest the promoter of the wildest theory, that of water filaments ;-) > Also, I still think an AC signal might be useful for detecting > filaments, and maybe determining something about their size and > makeup. Their conductivity should be a lot higher than air or air > with drops, especially at lower frequencies. It would also be > important to measure the liquid flow rate. IF it's filaments. This makes me think that I forgot to answer your question about how an ion stream could remain thin instead of expanding by self-repulsion, here is the "quantized ion flow" speculation I had made in an earlier post kindly forwarded by Robin on June 12: ---------- About the low current phenomenon, it occurs to me that a sufficiently low current ion stream, where the ions would form a clearly discrete dotted line rather than a continuous-looking stream, would not expand sideways by self repulsion as we have been assuming all along. Each ion would just follow the previous one at comfortable distance, only sigzaging slightly along the line of maximum field while it collides with neutrals every micron or so... ---------- Does it make any sense? Michel
