Electronics > Beginners

Differential measurements using isolated oscilloscope

(1/7) > >>

Aners:
How much difference in measurment accuracy can I expect from using an oscilloscope with isolated channels and single-ended probes versus using a non isolated oscilloscope but with differential probes?

I understand that it depends on the scope and the probes, but from a general perspective, what affects the measurment outcome?

Benta:
What exactly do you mean by "isolated channels"?
If you mean isolating the 'scope power supply by using an isolation transformer: don't do it. It's the most certain way to kill yourself.
There are numerous threads on this forum on this subject, as well as videos.

Aners:
Scopes like these:

https://www.tek.com/oscilloscope/tps2024b
https://cleverscope.com/products/CS448

David Hess:
There are two major considerations:

1. Differential probes have high input impedance on both connections but with common mode rejection limited both inherently and because of mismatched source impedances.
2. Isolated probes have low input impedance on the common side, chiefly because of common mode capacitance to ground, but essentially unlimited common mode rejection.

The result is that at higher frequencies where the common mode rejection of the differential probe falls, an isolated probe has an advantage in accuracy.  But an isolated probe can only be used where one of the connection points has a low impedance capable of driving its common mode capacitance to ground which can be 100 picofarads or more.

Note that common high voltage differential probes can have horrendous common mode rejection after a time because of a poor choice of substrate for the high impedance dividers and there are no provisions for the user to adjust it.  Isolated probes do not have this issue so might be considered more reliable.

Wimberleytech:
Not an answer but a comment related.

Not too long ago, I had a case where I needed to make a differential measurement on an off-line SMPS.  I decided to build my own differential amplifier using the AD624.  The output went to a single-ended probe to a TDS2022B.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod