>> >>
>> >>> >> > you see mainly at low frequencies, so if you make your measurements
>> >> > quickly, you won't see it.
>> >
>> >
>> >> > Since polystyrenes are strongly discouraged in new equipment design, I
>> >> > haven't bothered to look at how their DA is.
>> >
>> >> Why?
>> >
>> >On material properties, polystyrene and PTFE both look splendid: very low leakage.
>> >For mass production, though, styrene softens above about 100C. That's no good
>> >for a surface mount/reflow soldered component, so it has to be hand-assembled.
>> >
>> >PTFE and PPS go over 200C. Tin-silver-copper solder reflows at 217C.
>>
>> I told you older posts were more interesting. Unfortunately, Sally
>> doesn't live here any more. 2002....a vintage year.
>
>Looking back at the thread, I'm a bit surprised that nobody got onto roll-your-own AC (Blumlein) bridges.
>
>
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>has a section about small precison capacitors. Sadly, my copy (which I'd bought before 2002 ) is at home in Sydney, and I can't remember how much it has to say about measuring them.
>
>It would be hard to get a precision ratio transformer to work well at the sorts of frequencies you'd want to use to measure a 1pF capacitance, but the classic Blumlein centre-tapped transforner bridge would work fine for comparing small capacitors.
>
>In a national standards laboratory they'd be comparing the unknown capacitor with a Thompson-Lampard calculable capacitor
>
>
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>It's capacitance depends only on it's length, and typically they measure the length with a laser interferometer.
>
>The Thompson-Lampard theorem was published in 1956, when both the authors were working for the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO).
The old AAD meter (available at that time) exhibits about .01pF jitter. If all the OP wanted was .01pF resolution, then that might have been the quickest option.
Sort of takes the fun out of it, however.
RL