Maximum AC peak and RMS voltage my oscilloscope can measure - Page 1
Forum section: electronics / beginners

author: robsims
author_rank: Frequent Contributor
timestamp: June 27, 2025, 07:59:08 pm
content: Hi, i have a Hantek DSO 5072 oscilloscope and i want to make sure i don't damage my scope. I have attached the manual of the scope. I can calculate the Peak or RMS voltage, but since i'm a mechanical engineer i want to make sure i'm correct.My question is what is the maximum AC peak and RMS voltage i can measure with my scope with an 1X probe. Many thanks in advance

author: tooki
author_rank: Super Contributor
timestamp: June 27, 2025, 08:32:57 pm
content: The manual has a whole paragraph on it. Can you be specific on what part isn’t clear to you?

author: robsims
author_rank: Frequent Contributor
timestamp: June 27, 2025, 08:54:23 pm
content: the part where it says 2mV/div to 10V/div at input BNC. The oscilloscope screen is divided in 8 divisions. So max AC voltage is 4 divisions x 10V/div = 40 volts Peak. RMS voltage is 40 volts divided by the suare root of 2 = 28,2 Volts RMS.So for a 10X probe the max values are 400 Volts Peak and 282 Volts RMS. Am i correct?

author: Benta
author_rank: Super Contributor
timestamp: June 27, 2025, 10:58:46 pm
content: You're confusing the display borders with the input characteristics.On the input, stay below 300 V and you're fine. That the voltage displayed exceeds the display limits is unimportant and won't damage anything.

author: robsims
author_rank: Frequent Contributor
timestamp: June 28, 2025, 12:43:31 am
content: "You're confusing the display borders with the input characteristics" what do you mean by that? I want the the max AC voltage Peak and RMS i can measure with the 1X probes. Maybe i don't understand something

author: johansen
author_rank: Super Contributor
timestamp: June 28, 2025, 06:27:04 am
content: Quote from: robsims on June 28, 2025, 12:43:31 amKeep it within the display and you dont need to worry.Without knowing what is going on its impossible to give you better advice

author: radiolistener
author_rank: Super Contributor
timestamp: June 28, 2025, 06:28:36 am
content: Quote from: robsims on June 27, 2025, 07:59:08 pmNote that there is no way to correctly calculate Peak voltage from RMS voltage and vice versa if you don't know exact waveform of that signal. These are different measurement and while Peak voltage depends on the maximum peak voltage, RMS voltage depends on the signal waveform. The often used sqrt(2) multiplier is applicable for clean sine wave only, but not for other waveforms.Quote from: robsims on June 27, 2025, 07:59:08 pmAs documentation claims it support max 150 Vrms at x1 and 300 Vrms at x10. But also note that this is usually valid for very low frequencies (like mains 50 Hz) and maximum allowed voltage is rapidly decreased with higher frequency.As said in your manual, for 10x it drops down to just 13 Vpeak above 3 MHz, which is about 9 Vrms for clean sine.Quote from: robsims on June 27, 2025, 08:54:23 pmNo, max input limit is not related with V/div setting. It doesn't matter which V/div setting you set, it always limited with hardware frontend and as claimed in your manual is max 150 Vrms for x1 which is about 212 Vpeak for clean sine. But be careful, if waveform is not clean sine, the max allowed peak voltage will be lower.In other words, you cannot use it for mains measurements, because 230V mains have 230×1.1×sqrt(2)=358 Vpeak which is much higher than your scope hardware support.With 10x it has max 300 Vrms limit which almost fits with mains, but with very low margin, so using it is not safe, since mains may have random high voltage pulses up to 1-2 kV which can damage your oscilloscope. And any sine distortions of mains waveform also require higher voltage requirements.And be careful, because oscilloscope ground is connected to the mains connector ground pin, so if you accidentally touch it with mains line it can lead to severe results...

author: Vovk_Z
author_rank: Super Contributor
timestamp: June 28, 2025, 08:24:17 am
content: Quote from: robsims on June 27, 2025, 07:59:08 pmI just want to say that typical usual way to use a scope is to have 10x divider almost always except rare cases when you really need 1x.With 10x you have full frequency range, much smaller probe influence on the circuit, and much safer measurements for scope input circuitry.

author: Aldo22
author_rank: Super Contributor
timestamp: June 28, 2025, 10:28:03 am
content: Quote from: robsims on June 28, 2025, 12:43:31 amI think the confusion comes from the fact that there are two things:1. what is the maximum voltage the scope can measure in 1x? It's probably 80Vpp, that's relatively obvious from the screen.2. the other question is how much it takes to break the scope inputs. That's probably a bit more than 150Vrms in 1x.This is a little less simple, see radiolistener's comments.

author: robsims
author_rank: Frequent Contributor
timestamp: June 28, 2025, 11:56:43 am
content: Maybe i sound a bit dumb, but as a mechanical engineer i'm trying hard to acquire some knowledge about electronics. So for a clean sine wave the input limits for the scope at 10X are 300 volts RMS and 300 x 1.414 = 424 volts Peak. Am i correct?

author: JustMeHere
author_rank: Frequent Contributor
timestamp: June 28, 2025, 12:42:14 pm
content: https://eevblog.store/products/hvp70-70mhz-differential-probe?srsltid=AfmBOooYRcZOC9P57-gq2iEXRcYVikqA4G1Gyknn6pP-2mXEq8uAG3e4

author: Aldo22
author_rank: Super Contributor
timestamp: June 28, 2025, 01:06:19 pm
content: Quote from: radiolistener on June 28, 2025, 06:28:36 amIsn't this already included because the specification refers to the overvoltage category?E.g. CAT III 150VrmsShouldn't that be able to withstand transient voltages up to 2500V?Just asking, I'm never sure.

author: radiolistener
author_rank: Super Contributor
timestamp: June 28, 2025, 01:34:06 pm
content: Quote from: Aldo22 on June 28, 2025, 01:06:19 pmThat's a great question. Indeed, if a device is marked as CAT II 300 Vrms, it generally implies that its insulation is tested to withstand transient overvoltages up to 2.5 kV.However, it's important to note that this rating primarily refers to the insulation and safety margins, not necessarily the survival of the internal measurement circuitry. While the insulation might prevent a breakdown or arc during such a transient, the internal electronics may still be damaged if exposed directly to high-energy spikes.So even though the label suggests it should handle such transients in terms of safety, I personally wouldn't rely on it unless the manufacturer explicitly states that the input circuitry is protected accordingly. Better to stay cautious unless you’re sure it's designed for such conditions.

author: radiolistener
author_rank: Super Contributor
timestamp: June 28, 2025, 01:40:42 pm
content: Quote from: robsims on June 28, 2025, 11:56:43 amYes, this is correct.But note that this limit is stated for very low frequencies, close to DC, like mains 50 Hz. When frequency is higher than 100 kHz the thing become different and limits rapidly drops down to something like 10-25 V for 10x probe or 50 V for 100x probe.

author: robsims
author_rank: Frequent Contributor
timestamp: June 28, 2025, 01:54:36 pm
content: Many many many thanks Radiolistener. You're comment is simple, straightforward and right to the point. That's what i needed. Thanks also for that extra information about frequencies higher than 100 kHz. I will also take that into account when measuring signals. Many thanks again

author: golden_labels
author_rank: Super Contributor
timestamp: June 28, 2025, 05:23:42 pm
content: robsims: perhaps this picture makes the concept of derating clearer.It is for oscilloscope probes and taken from unrelated thread, so the exact values will not match. But the idea remains the same:The probe is rated for 300 VAC, but that value quickly drops as frequency increases.Don’t feel bad about your confusion. There is nothing wrong with you. It’s the documentation, that is poorly written. It squishes two separate ratings into a single description. One is CAT rating, which is about your own safety as the human operator. The other is input rating, which is about what the oscilloscope can take without losing its function. It’s not immediately clear, how to dissect it.