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Posted by ggherold on June 3, 2009, 10:54 pm
I've been measuring a lot of small capacitances (C) lately, I've been
using this old TEK X10 'scope probe with 8.5 pF of C. (All the new
probes stink, 12 - 16 pF) But It would be nice to reduce that number
and I'm willing to give up another order of magnitude in gain. So I
can stick 90 Meg ohm on the end of the probe. Is the parallel C that
I need to compensate it with about 1pF? I've seen this done before
but can't find the article or application note.

Thanks,
George Herold

Posted by John Larkin on June 3, 2009, 11:08 pm
On Wed, 3 Jun 2009 19:54:50 -0700 (PDT), ggherold@gmail.com wrote:

>I've been measuring a lot of small capacitances (C) lately, I've been
>using this old TEK X10 'scope probe with 8.5 pF of C. (All the new
>probes stink, 12 - 16 pF) But It would be nice to reduce that number
>and I'm willing to give up another order of magnitude in gain. So I
>can stick 90 Meg ohm on the end of the probe. Is the parallel C that
>I need to compensate it with about 1pF? I've seen this done before
>but can't find the article or application note.

Yup. You could use a gimmick capacitor, some twisted insulated wires,
and twist them to adjust compensation.

Or buy an AADE l/c meter. They are great.

John


Posted by ggherold on June 4, 2009, 2:31 pm
On Jun 3, 11:08=A0pm, John Larkin
> On Wed, 3 Jun 2009 19:54:50 -0700 (PDT), ggher...@gmail.com wrote:
> >I've been measuring a lot of small capacitances (C) lately, I've been
> >using this old TEK X10 'scope probe with 8.5 pF of C. =A0(All the new
> >probes stink, 12 - 16 pF) =A0But It would be nice to reduce that number
> >and I'm willing to give up another order of magnitude in gain. =A0So I
> >can stick 90 Meg ohm on the end of the probe. =A0Is the parallel C that
> >I need =A0to compensate it with about 1pF? =A0I've seen this done before
> >but can't find the article or application note.
> Yup. You could use a gimmick capacitor, some twisted insulated wires,
> and twist them to adjust compensation.
> Or buy an AADE l/c meter. They are great.
> John

Excellent I've ordered my own AADE. I've never tried the gimmick
gimmick, and I'll give that a whirl too. (PI)

George H.

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