DSO: How to read max. voltage specs? - Page 1
Forum section: electronics / testgear

author: Aldo22
author_rank: Super Contributor
timestamp: August 29, 2024, 01:33:24 pm
content: HiThis 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 ratings4. 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 SDS800XMax. input voltage: 1 MΩ ≤ 400 Vpk (DC + AC), DC~10 kHz (No CAT rating)Rigol DHO800Max. input voltage: CAT I 300 Vrms, 400 Vpk (DC + Vpeak)Hantek DSO2000Max. input voltage: 300VRMS (10X)Overvoltage Category 300V CAT IIFnirsi DSO-TC2Max. 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 ±40VSo 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 1Does 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.

author: Fungus
author_rank: Super Contributor
timestamp: August 29, 2024, 01:45:02 pm
content: 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.

author: Aldo22
author_rank: Super Contributor
timestamp: August 29, 2024, 02:34:49 pm
content: Quote from: Fungus on August 29, 2024, 01:45:02 pmThank 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.

author: Zero999
author_rank: Super Contributor
timestamp: August 29, 2024, 02:44:45 pm
content: 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.

author: Aldo22
author_rank: Super Contributor
timestamp: August 29, 2024, 02:48:59 pm
content: Quote from: Zero999 on August 29, 2024, 02:44:45 pmThank 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.

author: Fungus
author_rank: Super Contributor
timestamp: August 29, 2024, 02:59:31 pm
content: Quote from: Aldo22 on August 29, 2024, 02:34:49 pmWith 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 probealwaysif 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).Quote from: Aldo22 on August 29, 2024, 02:34:49 pmIt might not be able to measure/display that voltage but it should survive.

author: Aldo22
author_rank: Super Contributor
timestamp: August 29, 2024, 03:11:13 pm
content: Quote from: Fungus on August 29, 2024, 02:59:31 pmThank 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.

author: kripton2035
author_rank: Super Contributor
timestamp: August 29, 2024, 05:02:01 pm
content: never measure mains directly with your scopeuse a differential probe.or you will break the scope...there are topics about this on the forum, just search for it.

author: Aldo22
author_rank: Super Contributor
timestamp: August 29, 2024, 06:22:28 pm
content: Quote from: kripton2035 on August 29, 2024, 05:02:01 pmThanks, 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.

author: J-R
author_rank: Super Contributor
timestamp: August 29, 2024, 10:54:15 pm
content: 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.

author: Someone
author_rank: Super Contributor
timestamp: August 29, 2024, 10:56:42 pm
content: Quote from: Aldo22 on August 29, 2024, 02:34:49 pmRead 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.

author: KungFuJosh
author_rank: Super Contributor
timestamp: August 29, 2024, 11:08:31 pm
content: +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. 😉

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 08:22:06 am
content: Quote from: KungFuJosh on August 29, 2024, 11:08:31 pmThank 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)?

author: tautech
author_rank: Super Contributor
timestamp: August 30, 2024, 08:37:45 am
content: Quote from: Aldo22 on August 30, 2024, 08:22:06 amUntil you forget the probe is still set to 1x.

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 08:47:08 am
content: Quote from: tautech on August 30, 2024, 08:37:45 amThis 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.

author: newbrain
author_rank: Super Contributor
timestamp: August 30, 2024, 08:53:38 am
content: Quote from: Aldo22 on August 30, 2024, 08:47:08 amRemember 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

author: tautech
author_rank: Super Contributor
timestamp: August 30, 2024, 08:57:38 am
content: Quote from: Aldo22 on August 30, 2024, 08:47:08 amPartially.Your limits and the limits of your probes are most important.With the correct probe you can measure most anythingsafely.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.

author: Fungus
author_rank: Super Contributor
timestamp: August 30, 2024, 10:40:55 am
content: Quote from: tautech on August 30, 2024, 08:37:45 amOr 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.

author: pdenisowski
author_rank: Super Contributor
timestamp: August 30, 2024, 11:09:43 am
content: Quote from: Fungus on August 29, 2024, 02:59:31 pmAccording to the IEC, if it says “CAT II, 300V” it should withstand a transient of up to 2500V.

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 11:16:34 am
content: 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?

author: Fungus
author_rank: Super Contributor
timestamp: August 30, 2024, 11:26:30 am
content: Quote from: Aldo22 on August 30, 2024, 11:16:34 amThe people most likely to abuse it are, um, "newbies" so VRMS is best because it's a smaller number.

author: pdenisowski
author_rank: Super Contributor
timestamp: August 30, 2024, 11:28:06 am
content: Quote from: Aldo22 on August 30, 2024, 11:16:34 amAs apracticalmatter, 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.

author: Someone
author_rank: Super Contributor
timestamp: August 30, 2024, 11:35:39 am
content: Quote from: pdenisowski on August 30, 2024, 11:09:43 amBut no guarantees if it will still function afterwardso many different "ratings".

author: Someone
author_rank: Super Contributor
timestamp: August 30, 2024, 11:37:30 am
content: Quote from: Aldo22 on August 30, 2024, 11:16:34 amYes, you need to read the manual.Instruments are not self documenting.

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 11:58:27 am
content: Quote from: pdenisowski on August 30, 2024, 11:09:43 amThanks.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?

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 12:00:38 pm
content: Quote from: Someone on August 30, 2024, 11:37:30 amThere is nothing about this in the manual, only in the information quoted above.

author: pdenisowski
author_rank: Super Contributor
timestamp: August 30, 2024, 01:06:24 pm
content: Quote from: Aldo22 on August 30, 2024, 11:58:27 amWorking 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.

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 01:40:43 pm
content: Quote from: pdenisowski on August 30, 2024, 01:06:24 pmI 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..."

author: Fungus
author_rank: Super Contributor
timestamp: August 30, 2024, 02:13:48 pm
content: Quote from: Aldo22 on August 30, 2024, 11:58:27 amI 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. Justdon'tuse 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.

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 02:36:56 pm
content: Quote from: Fungus on August 30, 2024, 02:13:48 pmThank you!Quote from: Fungus on August 30, 2024, 02:13:48 pmThanks 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.

author: pdenisowski
author_rank: Super Contributor
timestamp: August 30, 2024, 05:02:14 pm
content: Quote from: Fungus on August 30, 2024, 02:13:48 pmAlthough 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.

author: Grandchuck
author_rank: Super Contributor
timestamp: August 30, 2024, 05:16:52 pm
content: Less than or equal to 5 volts for 50 ohm input. Is that true for most or all oscilloscopes?

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 05:50:30 pm
content: Quote from: pdenisowski on August 30, 2024, 05:02:14 pmThat's right, there is no such option on the DSO2000.

author: Fungus
author_rank: Super Contributor
timestamp: August 30, 2024, 06:05:57 pm
content: Quote from: pdenisowski on August 30, 2024, 05:02:14 pmCould be...Maybe they tried it, got a lot of returns "under warranty" and said "never again!"

author: pdenisowski
author_rank: Super Contributor
timestamp: August 30, 2024, 08:55:19 pm
content: Quote from: Grandchuck on August 30, 2024, 05:16:52 pmIn my experience, 5 volts is the "typical" max input voltage for a scope channel with its impedance set to 50 ohms.

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 09:54:52 pm
content: 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?

author: pdenisowski
author_rank: Super Contributor
timestamp: August 30, 2024, 10:08:16 pm
content: Quote from: Aldo22 on August 30, 2024, 09:54:52 pmI'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.SoCAT II, 300V has 2500V peak and (2500/12 ~=) 208 amps peak currentCAT III, 150V has the same peak (2500V) but since the test impedance is 2 ohms (vs. 12 for CATII), the max current is 1250 ampsSo 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.

author: Aldo22
author_rank: Super Contributor
timestamp: August 30, 2024, 10:34:33 pm
content: 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).

author: Someone
author_rank: Super Contributor
timestamp: August 30, 2024, 11:06:50 pm
content: Quote from: Aldo22 on August 30, 2024, 12:00:38 pmIf 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.

author: Someone
author_rank: Super Contributor
timestamp: August 30, 2024, 11:41:59 pm
content: Quote from: pdenisowski on August 30, 2024, 10:08:16 pmThat 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 pmDo 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.

author: Aldo22
author_rank: Super Contributor
timestamp: August 31, 2024, 09:20:50 am
content: Quote from: Someone on August 30, 2024, 11:06:50 pmHi someoneThereissomething 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, asI 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.

author: Fungus
author_rank: Super Contributor
timestamp: August 31, 2024, 10:52:48 am
content: The maximum voltage the hardware can handle without damage is "CAT II 300V"It'sTHATsimple. It really is.That's what CAT ratings are for, it's why they print them on the front of devices.

author: Someone
author_rank: Super Contributor
timestamp: August 31, 2024, 11:09:19 am
content: Quote from: Aldo22 on August 31, 2024, 09:20:50 am30Vrms != 80VppYou are adding assumptions and extrapolating from their limited information, which may or may not apply.Quote from: Aldo22 on August 31, 2024, 09:20:50 amThere 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.

author: Aldo22
author_rank: Super Contributor
timestamp: August 31, 2024, 11:11:33 am
content: Quote from: Fungus on August 31, 2024, 10:52:48 amGreat! 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!

author: minhtri0405
author_rank: Newbie
timestamp: November 27, 2024, 07:40:59 am
content: Quote from: Aldo22 on August 31, 2024, 09:20:50 amI have a pretty old OSC SDS1072CNL, but I just recently had a chance to use it. And like you I wondered if the 400Vpp written in the OSC specs is the maximum voltage applied to the OSC's BNC connector???. After reading many posts on eevblog and other sites I asked siglent and they said "yes", I illustrated with pictures to make sure I didn't misunderstand. Siglent confirmed that 400Vpp is the voltage at the BNC connector. Hope they don't exaggerate too much. Image attachments

author: Performa01
author_rank: Super Contributor
timestamp: November 27, 2024, 11:34:14 am
content: Quote from: minhtri0405 on November 27, 2024, 07:40:59 amNo, they certainly don't exaggerate at all. The 400 V limit is primarily related to the power handling limit of the input resistors (400 V causes already 160 mW dissipation in 1 megohm), as well as the max. voltage rating of the resistors and - depending on the particular design of the input buffer - maybe the max. voltage rating oc the AC input coupling capacitor. Of course, distances of "hot" traces to other conductive areas are of importance too.I can't show an application with 400 V right now, but happen to have a demonstration, where I measured 205 V DC with better than 0.1% accuracy using a somewhat more modern Siglent SDS1104X-E DSO. The 205 V were connected directly to the scope input, see attached screenshot in reply #8 of the following thread:https://www.eevblog.com/forum/testgear/are-scopes-expected-to-be-highly-accurate-on-dc-measurements/msg2144416/#msg2144416