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DSO: How to read max. voltage specs?

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Aldo22:
I happened to look at the specs of another Hantek (DSO5000P).
The description is more detailed, but I understand even less.
For CAT I and II it also says 300Vrms (10x) like mine, but for CAT III it says 150Vrms (1x).
What does that mean? Does anyone understand this?

pdenisowski:

--- Quote from: Aldo22 on August 30, 2024, 09:54:52 pm ---I happened to look at the specs of another Hantek (DSO5000P).
The description is more detailed, but I understand even less.
For CAT I and II it also says 300Vrms (10x) like mine, but for CAT III it says 150Vrms (1x).
What does that mean? Does anyone understand this?

--- End quote ---

I'm actually about to release a video on this topic ("Understanding CAT Ratings") but it won't be on YouTube for a few weeks. 

In the meantime:  there are four CAT ratings, each representing a higher voltage (and higher danger) environment.  In addition, within each CAT rating there are rated voltages.  (See attached slide).  The combination of these determines the maximum transient voltage.  Using that voltage and the "test impedance" at the bottom, you can calculate the max working current and max transient current.

So
CAT II, 300V has 2500V peak and (2500/12 ~=) 208 amps peak current
CAT III, 150V has the same peak (2500V) but since the test impedance is 2 ohms (vs. 12 for CATII), the max current is 1250 amps

So it should be clear (although maybe a little counterintuitive) that the CAT III, 150V device is "safer" than the CAT II, 300V device.

(But the CAT III device will also be more expensive, generally speaking)

The general recommendation (assuming you have choices) is to choose the category you will be working on, then a rated voltage within that category.

Normally, electronics (running on DC) is CAT I, household appliances or anything you plug into a wall is CAT II, indoor distribution wiring and things that are wired in (vs. plugged in) are CAT III, and the outdoor power connection from the utility company is CAT IV.

Hope that helps. I'll post a link to the video when it's live on the R&S YouTube channel.



Aldo22:
Thanks, but what does 10x and 1x mean there?
Actually, the CAT ratings are not so important to me at the moment.
I'm still trying to confirm that I can put a bit more than 30Vrms on the inputs (without probes).

Someone:

--- Quote from: Aldo22 on August 30, 2024, 12:00:38 pm ---
--- Quote from: Someone on August 30, 2024, 11:37:30 am ---
--- Quote from: Aldo22 on August 30, 2024, 11:16:34 am ---Is it possible for the manufacturer to print "300V CAT II" on the device if it only applies with the 10x probes?
--- End quote ---
Yes, you need to read the manual.

Instruments are not self documenting.
--- End quote ---
There is nothing about this in the manual, only in the information quoted above.
--- End quote ---
If there is nothing in the manual then the manufacturer has failed to provide the minimum information required (by various standards). Why use something if it is of questionable performance/safety/compatibility ?

If they don't state it, then you can't assume anything.

Someone:

--- Quote from: pdenisowski on August 30, 2024, 10:08:16 pm ---I'm actually about to release a video on this topic ("Understanding CAT Ratings") but it won't be on YouTube for a few weeks.
....I'll post a link to the video when it's live on the R&S YouTube channel.

--- End quote ---
That topic has been quite the landmine on this forum:
https://www.eevblog.com/forum/testgear/aneng-sz20-25-000-count-1uv-10na-20a/
https://www.eevblog.com/forum/testgear/trashy-meters-redux/
https://www.eevblog.com/forum/testgear/multimeter-cat-ii-rating-discontinuation/
Good luck!


--- Quote from: pdenisowski on August 30, 2024, 10:08:16 pm ---The combination of these determines the maximum transient voltage.  Using that voltage and the "test impedance" at the bottom, you can calculate the max working current and max transient current.

So
CAT II, 300V has 2500V peak and (2500/12 ~=) 208 amps peak current
--- End quote ---
Do R&S warrant accuracy, repeated operation, and survivability on those transients? Not just limited event safety withstand?
That would be a nice step up from the competitors.

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