[volt-nuts] Resistance standard

[NeonJohn]

On 08/23/2011 02:33 AM, Robert Atkinson wrote:
> I investigated this and both NIST (NBS) and NPL use refined mineral
> oil A.K.A liquid paraffin for room  to medium temeperature baths.
> This is a food/pharmaceutical  grade oil. It is a clear white oil,
> pretty much non-toxic and no disposal concerns. The materials in
> older standards will have been intened for immersion in this, not
> modern synthetic oils. A commercial food or confectionery supply
> house should be able to supply larger quantities at resonable cost.

To echo that thought, my company makes induction heaters.  For some
smaller ones we build up the resonating cap from CDE tubular
polypropylene caps soldered to bus bars.  Very high current (>1000 amps)
at low RF is involved so the caps need cooling.

I asked CDE about immersing them in mineral oil and in turn cooling the
mineral oil with a radiator.  They didn't recommend it.  I had been
running a prototype for several months without problems so I decided to
go ahead with the technique.  At the same time I set up a test.

I immersed 3 caps in the oil.  Every few months I take them out and
evaluate their parameters.  That experiment started 3 years ago.
Absolutely no change in any parameter or appearance.  Mineral oil is
about the most benign substance one can immerse electronics in.

I should also note that the oil has not gone rancid, changed colors,
filmed over, left deposits on the bottom of the container or otherwise
misbehaved.  The container is covered but not sealed.

The oil I use is USP grade intended as a livestock laxative.  A gallon
costs about $9 and a 5 gallon pail about $35 from the local Farmer's Co-Op.

John

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John DeArmond
Tellico Plains, Occupied TN
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