On Wed, 12 Jun 2002, Jim wrote:

>   "Using two variable capacitors"
>
>Dust and variable capacitors mentioned in the same
>sentance - is this a recipe for future trouble?

No, cos' he didn't mention metal (silver) oxide on the wiper. Of course he
could be clever and use a piece of RG174 coax to connect the moving part.
But he did not say so ...

>   - dust between plates
>   - dust in the bearings of the movable portion
>   - wear in the metal 'bearing'
>   - poor contact in the bearing for RF currents
>
>How about two fixed plates (of a cap) into which is
>moved a dielectric - to change the capacitance.

Weeelll, with 0.82 pF * (cm^2/mm) in air you better come up with a good
and I mean *good* readout scheme to achieve 5% accuracy over room
temperature and 10% supply voltage span imho. even with *water* (Epsilon-R
~= 80) as moving dielectric. Scott Dattalo could surely chip in here if he
would not be bound by NDAs and such,

>At least this way the dependence on a metallic
>bearing also carrying RF from one cap plate in a
>dusty environ is eliminated ...

Because the oxide would prevent any contact ? ;-)

Peter

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics