High Voltage measurement

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sdlgeiger
Posts: 4
Joined: Thu Dec 05, 2013 10:27 pm

High Voltage measurement

Post by sdlgeiger »

Hey Everyone

I just received my kit in the post and have built it. I adjusted the HV_Adjust as per the instructions and all is well.

My question is how can I accurately measure and adjust this voltage to that required for the tube?

With my stock standard sparkfun DMM, which has an internal impedance of 1Mohm and can measure up to 600V with +/- 1 to 5% and 1V resolution.
Currently if I measure the HV+ to GND I get from 75 volts to 126 volts. Not what I was expecting. I was expecting 400 volts to about 700 volts.

I see in the instructions that they suggest using a 1 G ohm resistor in series and then dividing out by the DMM internal resistance. I dont have a 1 G ohm anything.

Whats the go?
sdlgeiger
Posts: 4
Joined: Thu Dec 05, 2013 10:27 pm

Re: High Voltage measurement

Post by sdlgeiger »

I found this article which describes the problem...
http://ea4eoz.blogspot.com.au/2012/09/o ... probe.html

So the cheap multimeters have a typical 1M ohm internal impedance, so one needs to create a divider using the 1 G ohm resistor in series, and then measure the HV on a 200mv scale on the DMM.

Will have to hunt around for a 1 G ohm on the net... Must have precise voltage calibration :lol:
sdlgeiger
Posts: 4
Joined: Thu Dec 05, 2013 10:27 pm

Re: High Voltage measurement

Post by sdlgeiger »

Found some 1 G ohm resistors on ebay from a store in Hong Kong. $6 each incl delivery.

I will report back of my findings once I have received them.
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mightyohm
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Re: High Voltage measurement

Post by mightyohm »

The method you linked to works well - that's how I do it.
More details here: viewtopic.php?f=15&t=487
Let me know if you have any problems.
sdlgeiger
Posts: 4
Joined: Thu Dec 05, 2013 10:27 pm

Re: High Voltage measurement

Post by sdlgeiger »

Okay, My 1 Giga-ohm resistor arrived in the post today.

I have connected it to my multimeter, and read the voltage on the 2V scale.

I can confirm I am getting 297 up to 741 Volts on this geiger circuit.

This has allowed me to fine tune the voltage to 400 volts for the SBM-20 tube.

Happiness prevails!
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mightyohm
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Re: High Voltage measurement

Post by mightyohm »

Cool! Have fun with your kit!
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