Products > Test Equipment
High voltage oscilloscope probe
Hydron:
The dielectric constant with freon gas (the liquid is only a small fraction of the volume of the probe so can be ignored), or air, or butane gas for that matter, will all be ~1, no compensation change needed (note the manual doesn't say to re-compensate when used without freon, just that the voltage rating will suffer). You cannot substantially change it from 1 without changing from a gas fill to a liquid (e.g. the silicone in the P6015A, which did need design changes to be able to compensate for) or solid fill.
Using a different dielectric gas will only change:
- Breakdown voltage (gas properties and working pressure dependant)
- Probe internal pressure vs. temperature
- Safety
- Ozone depletion/global warming potential
alm:
According to this paper the breakdown voltage of butane at room temperature and atmospheric pressure is slightly lower than that of air. So what's the benefit of using butane?
Hydron:
I think people were looking at butane as it's similar in vapour pressure to the original Freon. Unfortunately it's likely that it's not as high a dielectric strength as the original, though the slightly increased vapour pressure should help a little. I didn't find any hard numbers with a quick search, hence my original question - that paper seems to be about butane flames, not sure it's applicable?
MarkL:
--- Quote from: Stray Electron on January 16, 2023, 01:39:53 pm ---...
I used to see a lot of those p6015 probes in the surplus since they couldn't get the freon to fill them with any longer. Is there another gas that could be used to fill them with that would allow them to be used to greater than 20 kV?
--- End quote ---
You might find this post interesting:
https://www.eevblog.com/forum/testgear/high-voltage-oscilloscope-probes-make-or-buy/msg4326361/#msg4326361
In the referenced AN-108, they debunk the butane fill and recommend a special silicone oil. It's not a Tek app note, but they appear to have done their homework.
Hydron:
Thanks for the link - suggests that a) dielectric constant can be entirely ignored for a gas fill (but not if you totally fill it with a liquid) and b) butane sadly doesn't have enough dielectric strength, which is what I feared :(
I think I'll be using butane for pressure testing only - don't want to re-do the seal in mine and fill it with the last of the freon only for it to all leak out again.
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