Re: Probe for rise/fall time measurement of 1kV floating signal

On Thu, 15 May 2008 05:18:32 -0700 (PDT), Francis
<yokedesign1@xxxxxxxxxx> wrote:

Dear all,

I would like to measure the rise and fall time of a short pulse over a
non-grounded capacitor. The pulse is 1kV amplitude and typical rise
and fall time are some ns. Pulse width is about 100ns.
I have in mind to use 2 Tektro P5100 probes connected on each side of
the capacitor and use A-B maths function of TDS5052B oscilloscope to
evaluate the signal performance. According to data***, P5100 is a
x100 probe with 250MHz BW (rise time 1.75ns) with loading of 10Meg and
2.75pF.
I was told that it would be better to use a differential probe P5205.
But this probe has 100MHz BW and loading of 4Meg / 7pF each side. I
have not such a probe today.
I would like to have a measurement error less than about 5ns.
I would appreciate your comment which method has the best accuracy or
any other proposal.
Best regards,

Francis



|
| coax
+---------c---r----r----==========-50r scope ch 1
|
|
|
your
cap
|
| coax
+---------c---r----r----==========-50r scope ch 2
|
|
|
|



Do this if you can stand a 2K or so AC load. Use the scope in channel
subtract mode.

The R's can be, say 1K 1206's or carbon comp/film parts; all are fine
at this speed. Match as needed for cmrr. Ground the coaxes at both
ends. Add attenuators at the scope inputs if the signals are still too
big.

Or you could do a balun sort of thing, depending on your exact
situation.

John




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