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The classical differential probe are non isolated. But it also exist differential probe that are isolated.

What is the interest of isolated differential probe with respect to a non isolated differential probe?

Here is a link of a differential probe non isolated and a differential probe isolated :

https://my.element14.com/pico-technology/ta044/probe-active-differential-hi-volt/dp/1667349

https://teledynelecroy.com/probes/high-voltage-optically-isolated-probes

Jess
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  • Maybe link the isolated probe you refer to? – Andy aka Mar 02 '23 at 10:47
  • Does this answer your question? [Attenuation in the circuitry of differential vs isolated probes](https://electronics.stackexchange.com/questions/527624/attenuation-in-the-circuitry-of-differential-vs-isolated-probes) – DKNguyen Mar 02 '23 at 14:06
  • Well I think that the answer of this question does not talk about common mode noise that could flow through a differential probe. That is not a question about CMRR but it looks like more EMC. I do not find nice informations about it ... TonyM is actually better answering to the question :) – Jess Mar 02 '23 at 17:23

1 Answers1

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Test equipment like an oscilloscope usually connects its probe grounds to its mains earth, for electrical safety and to ground the probe's cable shield to reduce the noise picked up by the measurement.

With a differential probe, neither of the two differential inputs is grounded and the probe has a max' differential input voltage range. However, the differential input circuit of the probe will have a 0 V rail and the probe will have a max' voltage for each differential input to this rail.

It is this input circuit 0 V rail that is connected to ground in a non-isolated probe and not in an isolated probe.

An isolated probe has isolation coupling (a silicon isolator IC or, in the past, a transformer) between its differential input circuit and the test equipment making the measurement. This removes (or greatly reduces) any effect of ground loops between the test equipment and circuit under test and allows a much higher max. voltage between either probe input and ground.

So the non-isolated probe is used where the test equipment can share a common ground connection with the circuit/equipment under test. And an isolated probe is used when the two cannot share a common ground for the reasons above. Because of the need for precision isolation circuitry, the cost of the isolated probe is usually higher.

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TonyM
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  • That is not the case for a differential probe whatever it is isolated or not – Jess Mar 02 '23 at 12:44
  • @Jess, that's a better comment that then made clear that it'd written the answer wrong :-) Should be corrected and clarified now. – TonyM Mar 02 '23 at 13:55
  • Hi @Jess, glad this made it clear and answered your questions and thanks for accepting the answer promptly. This comment chain isn't needed any more so, if you're happy to, please delete your comments and I'll see and delete mine, leaving the site tidier. – TonyM Mar 04 '23 at 12:11