Make X100 'scope probe from X10

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

 

[John Larkin]

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

 

On Jun 3, 11:08 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

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.  (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

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.