[sdiy] Being accurate

[MBEDTOM at aol.com]

In a message dated 10/8/2005 11:39:41 AM Central Standard Time, 
synth1 at airmail.net writes:


> About 10 years ago, I had to design a capacitance meter that could resolve 
> 10fF 
> (10 femtofarads) on a scale of 0 to 100pf. For $25. Working outside at -40C 
> to 
> +100C.
> 
> Any guesses how it was done?
> 
> Paul S.
> 
> 

Amplitude stabilized oscillator driving capacitance under test, then convert 
AC current passed, to capacitance?  Would probably need 100 KHz oscillator and 
some fancy footwork to make that $25 price tag.  Don't know if that would do 
it but am fresh out of guesses.

So what did you actually do?  +100C is pretty damned hot!  (Cool day in 
Texas, though.)

Peace.
Tom Farrand
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