Re: P6015A HV probe


Sure it makes a difference but it also makes a difference in
dielectric constant between liquid and gaseous form. I deliberately
used the numbers for dielectric strength in gaseous form.

I gather that freon 114 was deliberately used as a gaseous dielectric
by others for the same reason Tektronix used it; boiling below room
temperature allows it to positively displace air in the device and its
low vapor pressure allows simple low pressure construction and the
maintenance of a liquid reserve to maintain positive pressure. Butane
has all of those advantages as well but of course it is flammable but
I do not really consider that a serious problem in this application
where the volume is so low.

The slightly higher vapor pressure of butane over freon 114 should
somewhat make up for its lower dielectric strength if that is a
problem. In any event, it is cheap, readily available, and an
improvement over using nothing. I have been reluctant to purchase one
of the older probes but this changes my mind.

On Thu, 9 Nov 2017 19:09:26 +0000, you wrote:

Does it make a difference that it's in gaseous form?

On Nov 9, 2017, at 11:06 AM, David @DWH<mailto:@DWH> [TekScopes] <TekScopes@...<mailto:TekScopes@...>> wrote:

I never considered butane either. My only concern would be its
dielectric strength. Let's see ...

Freon 114 is 1,2-Dichlorotetrafluoroethane with a dielectric strength
of 2.52 compared to nitrogen. Butane has a dielectric strength of 1.5
or 1.7 compared to nitrogen depending on information source.

The breakdown voltage is further increased over nitrogen because the
freon 114 and butane are used at higher than atmospheric pressure.

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