On Fri, 14 Jun 2002, Roman Black wrote:

>Peter L. Peres wrote:
>> I have researched
>> variable capacitor position and angle sensing thoroughly enough to be able
>> to say that it works iff you find a way to reduce the sensing input
>> capacitance 10 to 20 times (from what is a normal IC input cap. of 5pF).
>> It turns out that this is VERY HARD to do lacking specialised parts. A
>
>Again I say use the cap to drive an osc, divide freq
>via hardware (counter chip) or via PIC prescaler etc
>and test freq against the PIC clock. All system
>capacitances are negated provided you can calibrate
>the system degrees/freq which will have to be done
>anyway. :o)

Say again, starting at 'negated' please, I've lost you there. A system
with a self capacitance in the 5pF range will induce a potential error of
50% when measuring something in the say 3-12pF range (depending on which
end of the range). All the systems that use low value capacitors as
sensors (f.ex. many low cost scales) use the differential system and use
low frequency and effective capacitance measurement. There are exceptions
to this of course. Of course you already know that an air capacitor is
also a thermometer, hygrometer, and manometer all in one.

Peter

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