To make these two messages from the thread "Re: Isolation transformers
are not a panacea [was: Variak talk]" easier to find in the archives,
here is a summary of them, with links to the messages, under a new
Subject heading.
Steve <ditter2@...> wrote an interesting piece on differential
probes, including:
1 - Why ordinary probes are resonant at certain frequencies if the
ground connection to the device under test is not connected.
2 - The value and potential limits of differential probes.
3 - Difficulties measuring power transistor drive voltages in the
few hundred millivolt range when they are both at 900V or more.
4 - Achieving differential measurements with a pair of equal length
cable P6009 probes. Apparently the DC gain can be finely adjusted
on these 100x attenuation 120MHz 1500V probes:
David <davidwhess@...> continued the interesting discussion:
with mention of success using this dual probe technique, keeping the
cables close together, adding a ferrite core around the two cables,
modifying other probes to achieve the required close match of
attenuations, and: "As Glenn mentioned in the concurrent Cheap Probes
thread, if you run your hand along the probe cable and the waveform
changes, then you have problems."
- Robin
