[volt-nuts] Small capacitance

Poul-Henning Kamp phk at phk.freebsd.dk
Fri Jan 13 16:48:07 UTC 2012


In message <E7EAFDAE-17F8-48DC-AC7B-F8E42CB367D0 at gmail.com>, Fred Schneider wri
tes:

>so I need a sturdy standard capacitance. Any suggestions, something
>using air will be best I think but two metal plates should be
>straight and mounted solid opposite.

I think a major part of your uncertainty is stray fields:  parallel
plates have them all over the place.

I read somewhere that "real metrologists" use a particular design
for which the theoretical value has an analytical solution.

I can't remember the geometry which was described, but using circular
symmetry is a pretty good bet, and coaxial would make even more
sense, because the electrical field is mostly contained.

Found it, where else but at BIPM:
	http://www.bipm.org/en/scientific/elec/calc_capacitor/

And here's a good slide-set:
	http://www.metas.ch/LesHouches/downloads/talks/24_Bachmair.pdf

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