Homebrew HV hiZ scope probe

[Fred Abse]

Well,i snooped around their site and could find no way to get or find
that catalog.
No way to get that description, etc.
Dead end.
The best i could find, using MOX as a 3-character selector for part
number, thengetting the PDF for the Max-Mox series,was a one page PDF
named res_maximox.pdf; page labeled 85.
Now i see (only since you pointed it out) the 0.60pF . On the basis of
my calculations, i do not see how it can be that large. I guess i will
have to make a rather sensitive capacitance
measurement device, as DVMs tend to imply the low value i calculated.

I got the catalog from the Ohmite site the same time this thread started.
Took a bit of digging.

Don't you have a proper LCR meter, or bridge? A DMM isn't really suitable
for measuring parasitic capacitance.

A "real" LCR meter, or impedance analyzer, is a must-have for any serious
work. You could use an old Q meter instead.

 

[Fred Abse]

See http://www.oil4lessllc.org/HV probes/ for updated PDF. Have added
two more scope pictures and modified closing notes.

This shows that the fundamental risetime is faster than 20nSec.

I've just reread the PDF, and beg to disagree.

"Probe 1Gohm-3.jpg" shows the step still rising at about 1.8 microseconds,
where it goes off screen.

Risetime is the time from 10% to 90% *of the final steady value*. Risetime
is at least 1.2 microseconds, possibly more. It doesn't show the final
value.


"Probe 1Gohm-3.jpg" doesn't contain enough information to calculate
risetime. It just shows the initial overshoot and ringing, ie. the
first half-centimeter of the previous photo,some of what you see will be
due to the cable.

What I see is an under-compensated probe.