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Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
I am building a couple of CW multipliers right now, and I was wondering if these 1.5kV voltmeters would be good for using for measuring voltage if I used them with a voltage divider. However, according to the seller, the DC resistance of the meter is 72 ohms. Could this screw up any readings I try to get with it at say... 30-150kV?
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
You would need a large string of resistors to get the proper voltage drop over 72 ohms... I would ask the seller what the required voltage is to get FS deflection. From that you can figure out the additional resistance you would have to add. You want the resistance to be pretty high as not to load down the multiplier too much.
Another way you can make HV meters is by getting a low current meter (~50-100uA FSD) and adding lots of high voltage resistors to it.
If you want to go all the way up to 150kV I would put the entire resistor string under oil so that your chain of resistors doesn't have to be as long and also it would reduce the losses due to corona.
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Thanks, Myke. How would I use a uA meter to measure voltage? If I know my ideal output, do I just use a resistor chain to give the maximum current deflection at open circuit voltage?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Firefox wrote ...
I am building a couple of CW multipliers right now, and I was wondering if these 1.5kV voltmeters would be good for using for measuring voltage if I used them with a voltage divider. However, according to the seller, the DC resistance of the meter is 72 ohms. Could this screw up any readings I try to get with it at say... 30-150kV?
72 ohms is ridiculously low for a voltmeter, they were most probably meant to be used with a series resistor to get full scale deflection at 1.5kV (so they are really amp meters). If no resistor was used, you would get a juicy 31 kilowatts (where is the smiley?) on the meter with 1.5kV, I'm not really sure if it would be happy...
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
You use a uA meter to measure the current flowing through the resistor. From that you can get the voltage. For example: at 10kV there will be 50uA going through a 200M resistor. So with that setup the FSD would be 10kV.
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Thanks guys. I just found a NOS pair of 50uA meters in his items for sale list for 15 bucks. With a 1Gohm resistor, these should have the deflection I want.
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Voltimeters on Ebay
(where is the smiley?) on the meter with 1.5kV, I'm not really sure if it would be happy... 