DSO: How to read max. voltage specs?

[Aldo22]

Is it possible for the manufacturer to print "300V CAT II" on the device if it only applies with the 10x probes?

Yes, you need to read the manual.

Instruments are not self documenting.

There is nothing about this in the manual, only in the information quoted above.

[pdenisowski]

I simply wonder whether Hantek can be so bold as to write 300V next to connections that can only handle 30V.

Working in T&M for almost 30 years, I’ve seen plenty of questionable claims, but (so far) max input voltage hasn’t been one of them.  If anything, specs for max input voltage / power are usually pretty conservative.  To be an order of magnitude off seems very unlikely to me.

[Aldo22]

I simply wonder whether Hantek can be so bold as to write 300V next to connections that can only handle 30V.

Working in T&M for almost 30 years, I’ve seen plenty of questionable claims, but (so far) max input voltage hasn’t been one of them.  If anything, specs for max input voltage / power are usually pretty conservative.  To be an order of magnitude off seems very unlikely to me.

I think so too, especially as it's a beginner's scope that doesn't come with a printed manual.
So all you see is 300V. Any normal person would understand this as max. input voltage, especially because other scopes are also specified with this value.
But, yes, "the proof of the pudding..." 

[Fungus]

I simply wonder whether Hantek can be so bold as to write 300V next to connections that can only handle 30V.

I doubt it very much.

Input impedance is probably 1M Ohm so 300V isn't likely to damage it - it's less than 1mA of current.

CAT ratings include transients though. That's where the doubts are.

This is academic though. Just don't use 1x probes for this check the switch and check a lesser voltage before probing to make sure the switch isn't broken.

Also: Get some fixed x10 probes (or even x100 probes) if you regularly want to look at mains AC. Reduce that 300V to 3V.

Even better: Get a differential probe and avoid the dangers of earthing as well.

[Aldo22]

I simply wonder whether Hantek can be so bold as to write 300V next to connections that can only handle 30V.

I doubt it very much.

Input impedance is probably 1M Ohm so 300V isn't likely to damage it - it's less than 1mA of current.

Thank you!

CAT ratings include transients though. That's where the doubts are.

This is academic though. Just don't use 1x probes for this check the switch and check a lesser voltage before probing to make sure the switch isn't broken.

Also: Get some fixed x10 probes (or even x100 probes) if you regularly want to look at mains AC. Reduce that 300V to 3V.

Even better: Get a differential probe and avoid the dangers of earthing as well.

Thanks Fungus, but really, I'll write it in bold letters now: "I don't want to measure mains with this oscilloscope" 
As I mentioned at the very beginning, I basically just want to know whether 60VDC directly at the input (1x, with AC coupling, so that it makes sense) will destroy my oscilloscope.
That's what it boils down to.

However, this thread is also there to discuss the sometimes confusing specifications of other devices.

[pdenisowski]

Input impedance is probably 1M Ohm so 300V isn't likely to damage it - it's less than 1mA of current.

Although the warnings about 1X vs 10X probes are very valid, there is an even larger danger if you accidentally leave the input impedance on 50 ohms vs 1 megaohm (“Hi-Z”).

I sometimes (half-seriously) wonder if the reason why most “hobbyist” scopes don’t have a 50 ohm input option is because it’s safer for new / casual scope users.

[Grandchuck]

Less than or equal to 5 volts for 50 ohm input.  Is that true for most or all oscilloscopes?

[Aldo22]

Input impedance is probably 1M Ohm so 300V isn't likely to damage it - it's less than 1mA of current.

Although the warnings about 1X vs 10X probes are very valid, there is an even larger danger if you accidentally leave the input impedance on 50 ohms vs 1 megaohm (“Hi-Z”).

I sometimes (half-seriously) wonder if the reason why most “hobbyist” scopes don’t have a 50 ohm input option is because it’s safer for new / casual scope users.

That's right, there is no such option on the DSO2000.

[Fungus]

I sometimes (half-seriously) wonder if the reason why most “hobbyist” scopes don’t have a 50 ohm input option is because it’s safer for new / casual scope users.

Could be...

Maybe they tried it, got a lot of returns "under warranty" and said "never again!"

[pdenisowski]

Less than or equal to 5 volts for 50 ohm input.  Is that true for most or all oscilloscopes?

In my experience, 5 volts is the "typical" max input voltage for a scope channel with its impedance set to 50 ohms.

[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]

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?

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]

Is it possible for the manufacturer to print "300V CAT II" on the device if it only applies with the 10x probes?

Yes, you need to read the manual.

Instruments are not self documenting.

There is nothing about this in the manual, only in the information quoted above.

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]

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.

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!

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

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.

[Aldo22]

There is nothing about this in the manual, only in the information quoted above.

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.

Hi someone

There is something about it in the manual and I have already shown that:



I just don't quite understand what it means.
That's what this thread is about: "DSO: How to read max. voltage specs?".

The sticking point is that the manual says: 300Vrms (10x).
The question was: What does (10x) mean in this case?
The print on the front panel (overvoltage category) does not say 10x.

But it's actually not safety-relevant for me, as I have nothing to do with mains.

Even if it means that it can only handle 30Vrms (1x), that's still 80Vpp (1x) or 800Vpp (10x). That's enough for me.
That would be no reason not to use the oscilloscope.

The only question is whether I would destroy the oscilloscope with e.g. 60VDC (1x).
But I would survive that and should that happen, I would buy a new scope.

So again, I just want to know how to interpret the specs and I've already learned a lot in this thread.
I'm not interested in looking at mains with this scope. I wouldn't know what for.

[Fungus]

The maximum voltage the hardware can handle without damage is "CAT II 300V"

It's THAT simple. It really is.

That's what CAT ratings are for, it's why they print them on the front of devices.

[Someone]

Even if it means that it can only handle 30Vrms (1x), that's still 80Vpp (1x) or 800Vpp (10x).

30Vrms != 80Vpp

You are adding assumptions and extrapolating from their limited information, which may or may not apply.

The only question is whether I would destroy the oscilloscope with e.g. 60VDC (1x).

There is not enough information given so far. Why not ask your distributor or the manufacturer ? They are responsible for your support of the product and any shortcomings in the documentation.

[Aldo22]

The maximum voltage the hardware can handle without damage is "CAT II 300V"

It's THAT simple. It really is.

That's what CAT ratings are for, it's why they print them on the front of devices.

Great! I hope so and I believe that too.

I just still don't know what 300Vrms (10x) means there.
Does it perhaps just mean that it can't display/measure 300Vrms in 1x?

Well, maybe I'll never know. It's not that important for me.

Thanks!