[time-nuts] Tek high voltage probes

[J. Forster]

Note that if you change the dielectric in the probe, especially to a
liquid, you may no longer be able to compensate it properly.

The higher dielectric constant will increase the stray capacitances.

Best,

-John

================



> On 9/22/11 10:34 AM, NeonJohn wrote:
>>
>>
>> On 09/21/2011 04:57 AM, David C. Partridge wrote:
>>> Howsabout HFC-236fa - very similar properties to R114 but not banned.
>>
>>>> Tektronix used a Freon in their 40 KV High Voltage probes. The Vapor
>>>> pressure of some of those compounds is low at 70F, but they do have to
>>>> be sealed.
>>
>> I use several of the Tek probes in my work (and of course am too cheap
>> to buy the newer solid dielectric ones).  When my freon ran out, I
>> searched around for a replacement fluid and found ordinary butane
>> straight from the Ronsonol can to be equal to or maybe even better than
>> the original freon.
>>
>
> Yes.. most hydrocarbons make a fine dielectric (viz. transformer oil).
> To a certain extent, density is key, which is why the halogenated ones
> are nice (F or C are more massive than H).  The other thing is that
> those halogens are electronegative which tends to suppress breakdown
> (why SF6 is great.. not only is it really dense, but it's also non
> flammable AND it's got fluorine in it)
>
> The halogenated ones are preferred in some cases because you can get
> other vapor pressures and/or they don't burn.
>
> There is, of course, a whole class of nice dielectric fluids based on
> halogenating double ring structures: PCBs.  They're really inert, great
> dielectric strength, immiscible with contaminants (no dissolved water,
> which ruins dielectric properties).  The problem is that there's an
> unavoidable carcinogenic contaminant (dioxin-like PCBs and PCDFs).  And,
> because they ARE so resistant to breakdown, they persist forever, and,
> unfortunately, are fat soluble and taken up by wildlife.
>
>
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