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Registered Member #60240
Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304
Hi
This is a Sensitive Research electrometer with four voltage ranges:
5 kV 10kV 20kV 30kV
The lowest easy readable voltage is 1kV in the 5kV range.
The voltage ranges could be changed mechanically by moving a slider:
I have two questions:
Please, who has similar electrostatic voltmeters and what is to say about the performance? For example determining the resistance of the voltmeter by measuring the decline of the displayed voltage after a short connection to a DC 25 kV terminal.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
What?
I think I have the same one.
It's not resistive, its mechanical!
On ours they are hard to see how it works inside, but on the really big one, I think its 100KVDC (two person lift), there is a door that you can open and see the carriage mechanism that causes the needle to deflect. The carriage deflects due to charge, it's a very precise capacitor if you will, and as the charge increases it is pulled together, its a fascinating instrument.
Registered Member #60240
Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304
Hi Hazmatt_(The Underdog)
You are quite right, this instrument is not resistive, the Coulomb interaction of two charges with different signs drives the pointer of the instrument.
I am interested in the quality of the insulation of your instrument, it could be around 10**16 Ohm. If a charged capacitor will be discharged by a high Ohm resistor the voltage of the capacitor is decreasing according to U(t) = Uo e**(-t/R*C). If the capacitance of your instrument is about 10 pF and the time constant R*C is about 100 seconds after 100 seconds your originally displayed voltage goes down to Uo/e. Then is your insulation resistance about 10**13 Ohm, also you can measure very low currents (10**-13 A) by simply counting seconds.
Please could you publish a picture of your "really big one" instrument as well as the dimensions, the weight and perhaps also the insulation resistance?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I imagine that above about 5kV the main losses would be due to corona discharge and some surface conduction over insulators so preventing contamination and cleaning are probably very important.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I was going to make a low capacitance meter to check my lab standard air capacitor, but any project like that takes me a long time because of my work, and other people's projects they want from me. But I am looking forward to doing it, if I get a chance. I would really like to measure capacitors that are small with high resolution XXX.XXXpF and precision.
The loss you are citing is called Dissipation factor. I would measure mine if I had a Megger. Now I suppose I could put it on my HP LCR meter, but it's probably going to read all zeros.
I do have a working Boonton Rx meter, which is a very precise instrument, but I'm betting the dissipation will read infinity on the Boonton as well. The lowest readable graduation is 100K, and you're saying the leakage on the meter is in the 10^13 range, which is fairly hard to measure. The dust on the instrument is going to throw it off at that point.
Now I don't have the really big one, it was at college. I was building another Tesla coil at the time and I was hoping we could use it to measure the coil, but it had to be tossed-out, and they are big. I couldn't save it because I had no room for it here at home. Here is an ebay listing for one:
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30 kV Sensitive Research electrometer
