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Probe into probes. What's up?

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BillyO:
I had some idle time today and decided to do some bode plots on the tek and no-name probes.  A bit pointless, I know, but ..  I only have an "improved" SDG1032X so could only go to 60MHz.  As expected they did just fine.  The behavior at the end is due to the sig. gen.

Top picture is the Tek, next the no-name and the last is the SDG1032X by itself.

David Hess:

--- Quote from: jonpaul on February 01, 2023, 09:40:49 pm ---Wideband fast measurements (as in the posts above) are seldom done on battery scopes.
--- End quote ---

But battery powered oscilloscopes commonly have galvanically isolated input channels, making them particularly useful for wideband isolated measurements on the primary side of off-line designs.  The switching waveforms on more recent off-line switching power supplies have transition times in the nanosecond range requiring 100+ MHz measurement performance.

The big advantage they have over using a high voltage differential probe is an essentially infinite common mode rejection ratio.


--- Quote from: Njk on February 01, 2023, 11:23:46 pm ---So in telephone modems, the common approach was to use a transformer. Later, the chips were introduced (pioneered by Silicon Labs, IIRC) that were using a capacitive digital link over an isolation barrier to communicate between the line part and the SELV part within the chip. And the last modem designs were transformer-less. I was thinking the same approach could be used to design a floating probe. Not of GHz BW, of course. A diff probe is totally different thing as it requires ground connection.
--- End quote ---

It has been done at various times.  The Tektronix A6902 is a good example which is fully documented, and there are modern faster probes.

Bud:

--- Quote from: jonpaul on February 01, 2023, 09:40:49 pm ---mains>>variac>>1:1 isolation transformer

--- End quote ---
Folks in the other thread must be getting a heart attack caused by your post :-DD

https://www.eevblog.com/forum/chat/do-you-guys-use-an-isolation-transformer-for-your-labworkbench/msg4675405/#msg4675405

bdunham7:

--- Quote from: David Hess on February 03, 2023, 12:15:29 am ---But battery powered oscilloscopes commonly have galvanically isolated input channels, making them particularly useful for wideband isolated measurements on the primary side of off-line designs.  The switching waveforms on more recent off-line switching power supplies have transition times in the nanosecond range requiring 100+ MHz measurement performance.

--- End quote ---

Yes, something like my TPS2024 has better real performance than even my A6909 isolator, let alone modern discount differential probes.  Here is a shot of me measuring the output of the Bodnar pulser using a P6139 (not properly compensated, but it matters very little) with just my fumbly hands and a regular ground lead--I didn't bother putting the ground collar thingy on it. 

David Hess:

--- Quote from: bdunham7 on February 03, 2023, 12:30:16 am ---Yes, something like my TPS2024 has better real performance than even my A6909 isolator, let alone modern discount differential probes.
--- End quote ---

Tektronix took advantage of their CCD based sampling technology to make a small and low cost sampling front end for that series of DSOs.  Once the high speed sampling is complete, the analog samples are convert at low speed and the digital data is transferred across the isolation barrier.

An all digital design would have required a high speed digitizer and pile of fast SRAMs for each channel making it much more expensive.  Tektronix had DSOs like that, but they were not portable and never had isolated channels.

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