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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I have been using these 'sticks' for some years now with zero failures
46 x (2M2, 0W5, VR37) resistors in series = 100 MOhm, 23 W nominal, per stick (46 x 2.2 = 101.2 MOhm but due to tolerances in the batch that I bought actual resistance = 100.4 +/- 0.2 MOhm each stick) (I had originally planned for 45 x 2.2 = 99 MOhm) I rate these sticks at 10 kV, 10 W, each, (50 or 100 uA is just nice for a moving coil meter), safely, reliably. (240 V per 0.1" hole-to-hole @ 10 kV) Add in series for 20, 30, 40 kV etc. add in parallel and/or series to load eht power supplies. I have used 33 kV peak 'flyback' spikes across each stick.. no problem no encapsulation/insulation, just VR37 resistors on 0.1" fiberglass matrix board, smooth/blobby soldering.
The other two sticks are 1.5KE350CP TVS diodes in series, also about 10 W each stick. one stick just clips my 5 kV, 23 mA OBIT, the other does not.
Or, of course, you can measure Zin for yourself. If you Google for 'how to measure input impedance of voltmeter' and similar forms of words you will find enough answers to fill a wheelbarrow.
I measured my meter's resistance with a resistor and a battery. Its 1M ohm. I used a cheaper meter for this experiment.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
the good news is ; oscilloscope probes such as x1,x10, x100, x1000 can be used directly into your meter as oscilloscope inputs are nominally 1 MOhm. convert your meter leads to a BNC connector. e.g. or or etc. for a 10 MOhm input meter, add 1M1 across the meter leads, (or 1M + 220 K pre-set resistor for callibration)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
ScottH wrote ...
I measured my meter's resistance with a resistor and a battery. Its 1M ohm. I used a cheaper meter for this experiment.
This sounds sensible to me, Mr Scott, as it means you've 600 μA going in there, and 360mW getting wasted on your 600V range, but you ask folk like Sulaiman and Klugsmith who have spent a lot more time thinking about this kind of thing than I ever have.
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Will Connecting Several Multimeters in Series Increase the Voltage Rating?
