Re: HV voltage divider

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

My high voltage probe has a NE2 bulb across a 1 meg resistor at the meter
end. A 10 meg meter across a 1meg gives little error and if the probe arc s
over the neon bulb shorts out the spike protecting the meter. The neon bulb
is out of the circuit until about 90 volts when the neon fires.
     Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Fri, 01 Mar 2002 21:59:01 -0700
> To: tesla-at-pupman-dot-com
> Subject: Re: HV voltage divider
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Fri, 1 Mar 2002 22:20:01 -0700
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jimlux-at-earthlink-dot-net>
> 
> Most commercial dividers have a vacuum spark gap (like those in surge
> protectors) across the bottom resistor, just in case the big resistor
> flashes over.  And, as another poster pointed out, make sure the ground
> clip doesn't come off, or your voltmeter floats up to HV. This is one
> reason I like measuring the voltage across the resistor, rather than a
> series meter... If the thing flashes over, a series meter winding acts like
> a fuse (it's really tiny wire), and then the case of the meter floats
> up..., or it arcs inside, or..in general "bad things" happen.
> 
> Tesla list wrote:
>> 
>> Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <davep-at-quik-dot-com>
>> 
>> Tesla list wrote:
>> 
>>> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
>> <jimlux-at-earthlink-dot-net>
>> 
>>> Exactly how you'd do it....
>>> Is the meter impedance really 10 Meg, or is it 11Meg?...
>> 
>> Concur.
>> with one minor comment:
>> Suggest checking the power rating of the high meg resistor.
>> (yes.  The resistance is high, so the currents low, BUT THE
>> Voltages high.  Also look at the sparkover possibilities
>> 'along' the multiplier R.  (One such probe i ahd worked the
>> resistor in liquid freon...)  If the high r resistor fails,
>> or sparks over, the voltmeter is toast....
>> 
>>> You can always calibrate it with a known source...
>> 
>>> Tesla list wrote:
>> 
>>>> Original poster: "Richard Williams by way of Terry Fritz
>>> <twftesla-at-qwest-dot-net>" <richardwwilliams-at-earthlink-dot-net>
>> 
>>>> I have a 990meg ohm resistor salvaged from a HV DC probe whose
>>>> meter was shot.  Can I add a resistor in series, 10 meg ohm?, to
>>>> ground to measure HV? Haven't tried it since I'm leary of inflicting
>>>> damage to my digital meter since I've never done this before. Input
>>>> impedence of the meter at the 700vac range is 10meg so would that
>>>> "look" like a 5 meg resistor overall?
>> 
>> best
>> dwp
> 
> 
>