DSO: How to read max. voltage specs?

[Aldo22]

Hi
This is something I don't understand but would like to understand in order not to damage my oscilloscope.
It's not about probes/attenuators or RF effects but just the basic understanding of how much voltage can be applied directly to the BNC (DC to 1kHz for example).
If you compare the specs of different scopes, you will notice the following variants:

1: Specifications in Vrms / Vpk / Vpp (where I assume e.g. 300Vrms > ~400Vpk -> ~800Vpp)
2. Values in x1 or x10 mode.
3. Additional CAT ratings
4. it is not always clear whether the maximum voltage to avoid damaging the device is meant, or the maximum measurable voltage.

Here are a few examples of specs:

Siglent SDS800X
Max. input voltage: 1 MΩ ≤ 400 Vpk (DC + AC), DC~10 kHz (No CAT rating)

Rigol DHO800
Max. input voltage: CAT I 300 Vrms, 400 Vpk (DC + Vpeak)

Hantek DSO2000
Max. input voltage: 300VRMS (10X)
Overvoltage Category 300V CAT II

Fnirsi DSO-TC2
Max. input voltage: 1:1 probe: 80Vpp (±40V), 10:1 probe: 800Vpp (±400V)


What does it all mean?
I find the Fnirsi most understandable, with the ±40V

So Rigol and Siglent can withstand 300Vrms on the BNC (1x)? But they can't measure it with max 10V/div?
The Hantek specifications seem to me to be based more on the maximum measurable voltage (8x 10V/div).
Although it says 300VRMS (10X), it has CAT II, whereas the Rigol has CAT 1

Does anyone have a clue?
Simple question, as an example of what I'm asking: Will the Hantek break if you apply +60V DC to the BNC?

Thanks for any enlightenment. 

[Fungus]

The number printed on the front is for low frequencies only and is the maximum voltage at the BNC to avoid damaging the device.

(ie. with a 1x probe)

It will get significantly lower at high frequencies, but that's a whole other topic.

[Aldo22]

The number printed on the front is for low frequencies only and is the maximum voltage at the BNC to avoid damaging the device.

(ie. with a 1x probe)

It will get significantly lower at high frequencies, but that's a whole other topic.

Thank you!

On the front, it says "300V CAT II".
The manual says: "300VRMS (10X)".

What does that mean? 10x?
In other words, can I put 230V mains on the BNCs without breaking it?
It can't measure that anyway with max. 10V/div.

[Zero999]

x10 presumably means with a x10 probe, i.e. a probe which divides the input by 10 and applies frequency compensation for the cable.

It's generally considered a bad idea to connect an oscilloscope's output directly to the mains. The chassis shares the same earth as the mains neutral, which can result in high currents, blown fuses/breakers and at worst smoke, fire and electric shock. A differential probe is the correct way to use an oscilloscope at mains voltages.  There are other ways, but one has to ask such questions, they clearly lack experiance and competence to do it safely.

[Aldo22]

x10 presumably means with a x10 probe, i.e. a probe which divides the input by 10 and applies frequency compensation for the cable.

It's generally considered a bad idea to connect an oscilloscope's output directly to the mains. The chassis shares the same earth as the mains neutral, which can result in high currents, blown fuses/breakers and at worst smoke, fire and electric shock. A differential probe is the correct way to use an oscilloscope at mains voltages.  There are other ways, but one has to ask such questions, they clearly lack experiance and competence to do it safely.

Thank you.

You misunderstood me a bit.
I do know what 10x means. I'm just wondering what applies: The manual or the print on the front of the device?

And no, I have no intention of connecting the oscilloscope to mains.
I just want to know what the specs mean, as the thread title says.

[Fungus]

On the front, it says "300V CAT II".
The manual says: "300VRMS (10X)".

What does that mean? 10x?

With a 10x probe.

If it says "300V CAT II" on the front then it should withstand 300V RMS at the BNC.

Me? I wouldn't do it. I'd use at least a 10x probe always if I was looking at mains, maybe even a 100x probe if I was looking at mains all day long (they tend to have better insulation on them).

It can't measure that anyway with max. 10V/div.

It might not be able to measure/display that voltage but it should survive.

[Aldo22]

If it says "300V CAT II" on the front then it should withstand 300V RMS at the BNC.
..
It might not be able to measure/display that voltage but it should survive.

Thank you, that's the answer I was looking for. 

I didn't actually want to do anything with mains. If I have to, then I use a battery-powered scope.
As I said above, I wanted to know if I could apply +60V DC to the BNCs, for example.
If you read the specifications as 10x and not 1x, then the maximum would be +42V DC.

[kripton2035]

never measure mains directly with your scope
use a differential probe.
or you will break the scope...
there are topics about this on the forum, just search for it.

[Aldo22]

never measure mains directly with your scope
use a differential probe.
or you will break the scope...
there are topics about this on the forum, just search for it.

Thanks, but it was never my intention to measure mains with this grounded benchtop scope.
If I want to stare at a 50Hz sine wave, I use the built in AWG. 
I just wanted to know how to interpret the specs.
It can't hurt to know the limits.

[J-R]

Didn't see this mentioned, but the relationship between RMS, Vp and Vpp depends on the waveform.  For example, with a triangle wave, 520V peak is 300V RMS.

[Someone]

On the front, it says "300V CAT II".
The manual says: "300VRMS (10X)".

What does that mean? 10x?
In other words, can I put 230V mains on the BNCs without breaking it?
It can't measure that anyway with max. 10V/div.

Read the manual, that is one of the mandatory steps in making safe measurements. What is printed on the casing is only a reminder and may be for some specific configuration such as with the supplied probes attached.

[KungFuJosh]

+1 for being careful with Vrms. Neither the Rigol nor Siglent want to see peak voltages above 400V.

The "scope" that says "300V (10X)" likely means that the "scope" itself can't go above 30V, but they want to pretend they're cool like the big kids. 😉

[Aldo22]

The "scope" that says "300V (10X)" likely means that the "scope" itself can't go above 30V,

Thank you.
In principle, even the pessimistic interpretation does not limit what I can practically measure.
30Vrms sine (x1) is still 85Vpp, so it fills the scale (8x10V/Div).
It's really all about the safety margin.

The only problematic (real life) scenario I can imagine for my purposes is if I tried to measure ripple on a 60V PSU (1x, AC coupling, max. 42Vpk).

Would that be a real problem (in the pessimistic interpretation)?

[tautech]

The "scope" that says "300V (10X)" likely means that the "scope" itself can't go above 30V,

Thank you.
In principle, even the pessimistic interpretation does not limit what I can practically measure.
30Vrms sine (x1) is still 85Vpp, so it fills the scale (8x10V/Div).
It's really all about the safety margin.

Until you forget the probe is still set to 1x. 

[Aldo22]

Until you forget the probe is still set to 1x. 

This thread wasn't really about probes, it was about the maximum voltage on the input (BNC).
It's not really a problem for me as I never actually go above 30VDC or 25Vpp.
Even the 60VDC question was rather hypothetical for me.

But yes, more safety margin is certainly better.
Knowing the limits of the device is important in any case.

[newbrain]

It's not really a problem for me as I never actually go above 30VDC or 25Vpp.

Remember also that the stated limits are for low frequencies.
Siglent correctly put a 10 kHz limitation on the quoted figures.

Front-end derating at radio frequency (even at short-wave levels) has 'burnt' more than one young player.
See, e.g., https://www.tek.com/en/support/faqs/what-are-maximum-voltage-limits-tds-oscilloscopes-and-how-do-limits-change-over-frequen

[tautech]

Until you forget the probe is still set to 1x. 

This thread wasn't really about probes, it was about the maximum voltage on the input (BNC).
It's not really a problem for me as I never actually go above 30VDC or 25Vpp.
Even the 60VDC question was rather hypothetical for me.

But yes, more safety margin is certainly better.
Knowing the limits of the device is important in any case.

Partially.

Your limits and the limits of your probes are most important.
With the correct probe you can measure most anything safely.

Gone are the days when we floated a scope as differential probes are cheap and readily obtainable now whereas that practice was downright dangerous despite the fact that many of us did it. 

[Fungus]

Until you forget the probe is still set to 1x. 

Or if you have children/visitors and they like to play with the little switch.

I still think the most sensible thing I ever saw in a 'scope is that Micsig supplies fixed 10x probes with theirs.

[pdenisowski]

If it says "300V CAT II" on the front then it should withstand 300V RMS at the BNC.

According to the IEC, if it says “CAT II, 300V” it should withstand a transient of up to 2500V.

[Aldo22]

Thank you for all your contributions.
You can of course fill books about probes, safety, high frequency etc. but my question is really very limited.
I just want to know how to basically interpret the max voltage specs.
Or rather, I want to make sure that I am reading them correctly.

For example, one may wonder why the Rigol and Hantek specifications are in Vrms. Actually, Vpk would be less misleading, wouldn't it?
Is that just because people compare it with mains voltage?

Can one safely deduce from this that e.g.
30Vrms -> 42.5Vpk?
Does 42.5Vpk correspond to the maximum DC voltage, or is there something else to consider?

Is it possible for the manufacturer to print "300V CAT II" on the device if it only applies with the 10x probes?
Wouldn't that be grossly negligent, or does this happen more often?
Is this even allowed to be sold in the EU if it only applies under this restriction?

[Fungus]

For example, one may wonder why the Rigol and Hantek specifications are in Vrms. Actually, Vpk would be less misleading, wouldn't it?
Is that just because people compare it with mains voltage?

The people most likely to abuse it are, um, "newbies" so VRMS is best because it's a smaller number.

[pdenisowski]

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

As a practical matter, it’s really the probes that determine the safety more than the channel inputs. Most top tier scope manufacturers (including R&S) don’t indicate or specify CAT ratings for channel inputs.  For us, the only exception is our RTH handheld scope since one of its target markets is very high voltage (CAT III/IV) measurements.  Quality single-ended probes and most differential probes will have CAT ratings printed on them.

It’s worth noting that the IEC specifies CAT ratings but does not verify compliance. There are some (mostly DMM) manufacturers who “design to” a rating but never have their device tested by a third party like UL, CSA, TÜV, etc. 

[Someone]

If it says "300V CAT II" on the front then it should withstand 300V RMS at the BNC.

According to the IEC, if it says “CAT II, 300V” it should withstand a transient of up to 2500V.

But no guarantees if it will still function afterward so many different "ratings".

[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.

[Aldo22]

According to the IEC, if it says “CAT II, 300V” it should withstand a transient of up to 2500V.

Thanks.

To be honest, I'm not really interested in transients here.
I simply wonder whether Hantek can be so bold as to write 300V next to connections that can only handle 30V.

I mean, it's "only" Hantek, but they've been selling their devices worldwide for a few years now.

Would they risk a lawsuit just for the fun of printing BS specifications on the device?