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I have designed a mains powered flyback. As a newbie I am well informed about the danger of mains voltage if measured incorectly.

Still I want to measure a few points in my circuit to better understand it.

I am aware that isolation is a must to deal with mains voltage, therefore I am looking for an isolated differential probe.

There are 3 options that I found:

  1. Hantek HT8100 "Isolated Diff Probe" for 200€ https://www.hantek.com/products/detail/6163
  2. Pico TA041 "Active Diff Probe" for 400€ https://www.picotech.com/accessories/active-differential-high-voltage/25-mhz-700-v-differential-probe
  3. Rigol PHA0150 "Diff Probe" for 800€ https://rigolshop.eu/accessories/probe/pha0150.html

My question is:

  1. Some of the options do not mention if it is "isolated" (TA041 and PHA0150) but they write it as measurement scenario for use "HV isolation measurement". Can I still use this to safely measure mains?
  2. My osciloscope is from Rigol, and it is recommend to use the PHA0150 from the same brand Rigol for diff probe so that no compability issue arise. The HT8100 offer the same specifications with a fourth of the price and mention that it is "isolated". What aspect should I be worried of in terms of compability compared to if its isolated or not?
  3. Is it safe to use TA041 "Active Diff Probe" for mains? does "Active" also provide protection for measuring mains?
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  • \$\begingroup\$ Please provide data sheet links within your question to all equipment listed. \$\endgroup\$
    – Andy aka
    Commented Aug 20 at 9:05
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    \$\begingroup\$ If you power your circuit from a mains isolation transformer, then all of your isolation issues go away. \$\endgroup\$
    – Neil_UK
    Commented Aug 20 at 9:16
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    \$\begingroup\$ Do you think it's a good idea to buy cheap Chinese brands for this? Oops the isolated probe wasn't quite isolated, it turns out. The epitaph on the tombstone could be: "I saved 100€ by shopping from Aliexpress". \$\endgroup\$
    – Lundin
    Commented Aug 20 at 9:34
  • \$\begingroup\$ @Neil_UK True. However I want to know if it safe to use "Active" diff probe if no isolation transformer is used. The answer will provide me with knowledge and I also want to invest for a probe that I can use in multiple cases with being safe in mind. \$\endgroup\$
    – FrancisS
    Commented Aug 20 at 14:45
  • \$\begingroup\$ @Lundin My intention is not purely cutting cost by buying chinese brand alone. My first priority is safety and thus "isolation" is needed. I just wonder why the other does not specifically mention "isolation" and cost higher. And if it true that the other are not isolated, can I still use it to measure safely without blowing my osci? If not do you have any recomendation what can I use to measure mains safely? \$\endgroup\$
    – FrancisS
    Commented Aug 20 at 14:53

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It would be irresponsible of us to assert that any of your particular proposed commercial probes are safe for you to use on equipment connected to the mains. It is up to you to see whether any of them are actually rated for direct mains connection (a stricter requirement than merely being able to withstand x number of volts), and whether you trust that rating.

The advice for working on mains equipment is to isolate it from the mains using an appropriately rated mains isolation transformer, for safety.

Personally, I would use both an isolation transformer, and a high voltage probe, meaning that two faults are required before the measurement system becomes unsafe.

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