Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
On 24 March 2018 at 17:34, Jeremy Nicholswrote: > I made a high-value resistor using motor oil and a couple of stainless > bolts. It worked for what I was doing (testing an HP-425A > Microvolt-Ammeter) but calculated as only 8,500 Megohms. > > Jeremy > I had some discussions some time ago about using oil as a dielectric in a capacitor with someone at NPL. He said the loss of both cyclohexane and Polydimethylsiloxane (PDMS = silicon oil) is very low. He said the only way I would measure the loss of them was a resonate method, and detecting small changes in Q. My thoughts on putting them as the dielectric in a capacitor and measuring on an LCR meter would not work, nor would my transmission line. I had already satisfied myself that using a coaxial probe and VNA would not work. As he said, cyclohexane is nasty stuff, but PDMS is much more environmentally friendly. Dave ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
On 03/22/2018 09:07 PM, Bob Albert via volt-nuts wrote: > I found several electrostatic voltmeters on ebay. The brand I remember is > Sensitive Research. I have an electrostatic voltmeter (photo attached) that I no longer use that I'd part with for $50. This thing is big and heavy so shipping will probably be $100. It is mechanically sensitive enough that I'll probably need to build a wooden crate and pack that inside a large box filled with with padding. A local pickup would be wonderful. I live near Knoxville, TN and would go maybe 100 miles to meet someone. We have a motorhome and that would be the start of a nice trip. There are two kinds of electrostatics. The first type is like the ones currently on sleazebay. Relatively small, phenolic block input terminals and conventional internal wiring. Very high impedance but no where near infinite. Good enough to measure, say, the screen voltage on a tube but not suitable for measurements where the input impedance must be essentially infinite. Nuclear radiation ion chambers, for example. The second one is like the one pictured. Designed to have as close to infinite input impedance. That huge input tower is not for voltage withstand - this is a 2500 volt meter - but to lengthen the creepage path to ground. I sent this unit to a calibration lab about 10 years ago. With the tower carefully cleaned and a new dessicant pack inside, they could not measure the input impedance. The only practical flaw is that there are a few pF of capacitance between the plates that must be charged. Once the meter is deflected, there is no current flow. To satisfy myself that it was truly infinite impedance, I connected a 2000 volt power supply to the unit through the resister used in the Fluke 40kV high voltage probe. It took a couple of seconds for the capacitance to charge but once deflected, the electrostatic read the same value as the voltage output of the supply to within a minor division. Anyway, this instrument is available if anyone wants it. John -- John DeArmond Tellico Plains, Occupied TN http://www.tnduction.com<-- THE source for induction heaters http://www.neon-john.com<-- email from here http://www.johndearmond.com <-- Best damned Blog on the net PGP key: wwwkeys.pgp.net: BCB68D77 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
I made a high-value resistor using motor oil and a couple of stainless bolts. It worked for what I was doing (testing an HP-425A Microvolt-Ammeter) but calculated as only 8,500 Megohms. Jeremy On Sat, Mar 24, 2018 at 10:18 AM Mark Simswrote: > Many years ago, there was an article (in Popular Electronics?) that > needed a very high value resistor. They built it by drawing a line > between two terminals with Higgins India Ink. No idea if the ink is still > made the way it was 50 years ago... > > > > > So how does one make ones own resistor? > ___ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > -- Sent from my iPad 4. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
[volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?
Many years ago, there was an article (in Popular Electronics?) that needed a very high value resistor. They built it by drawing a line between two terminals with Higgins India Ink. No idea if the ink is still made the way it was 50 years ago... > So how does one make ones own resistor? ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.