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How to check a 230VAC sine/modified wave with an oscilloscope (FNIRISI 1013D)
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juan3211:
Hi guys, I am newbie with oscilloscopes.
I have an 1013D between Aliexpres and my home.
I have a doubt about this.

I want to check sine waves from several inverters. (230VAC)

I have read that with the 10x probe, this oscilloscope is capable of measure up to 400v

In oscilloscopes' specs, are these values peak or peak to peak (I mean, from -400 to 400 or -200 to 200)?
I have found different answers

This is important. If 400v specification is from -400 to 400, then I could use 10x probe to check pure sine inverter wave form

If 400v is peak, then I can't

Another question is: imagine that the previous answer is that I can measure only 400v (-200 to 200). Is it better a 100x probe or a 10x little transformer and use the included 10x probe ? Does transformer change/disturb/smooth the output sine wave of an inverter ? Even with load connected to inverter ?

Could you guys please ask me first answer? And if I need a 100x probe, for my use may be better/cheaper a little transformer that, besides, I already have ?

OF COURSE, i will use it in battery mode, without connecting anything to USB port.
I also know about risks of such high voltages.

Thanks a lot.

SPECS:
wasedadoc:

--- Quote from: juan3211 on March 18, 2023, 10:20:43 pm ---i will use it in battery mode, with connecting anything to USB port.
--- End quote ---
...withOUT connecting anything to USB port.

At such low frequencies you can get adequate performance by using a few suitable resistors to make a voltage divider.
alm:
I'd expect 400V max to be 400V rms, but on these scopes I wouldn't want to push them to their maximum ratings, so I wouldn't use 10x probes for probing mains.

I'd say a transformer is better from safety point of view (it will provide galvanic isolation in addition to attenuation), but a 100x probe will give better bandwidth. I'd expect a small mains transformer to have a bandwidth up to a few kHz, so I would expect that to be fine to get a decent number of harmonics. If you're not using a transformer, then I'd make sure you are not connecting the ground lead to anything other than ground. Not neutral, not phase, just ground. With a transformer you can clip the ground lead on either side of the secondary of the transformer. Without transformer, you may have to use two probes in subtract (CH2-CH1) mode if you need to prove both phase and neutral, although you may get a good enough signal if you just measure between ground and phase.

Even if you have a 100x probe I think a transformer would still be useful for the galvanic isolation, though you would probably just use a 10x probe with the transformer.
wasedadoc:

--- Quote from: alm on March 18, 2023, 11:21:01 pm ---I'd expect 400V max to be 400V rms,

--- End quote ---
I would not expect that.  Scopes are used for looking at all kinds of waveforms not just sine waves.  If looking at a waveform that is alternating between +400v and -400v (both "flat tops") its RMS is 400v.  The sqrt(2) factor does apply in that case or more generally.

My interpretation of the spec is 400v peak from zero in either direction.  INCORRECT - See update below.

Also my interpretation of the opening post is that the 230 v is not AC mains and the concepts of Live/Neutral or Phase/Ground etc may not apply.  The OP could clarify that.

Update:  Read the extract from the 1013D's manual.
alm:

--- Quote from: wasedadoc on March 18, 2023, 11:40:50 pm ---
--- Quote from: alm on March 18, 2023, 11:21:01 pm ---I'd expect 400V max to be 400V rms,

--- End quote ---
I would not expect that.  Scopes are used for looking at all kinds of waveforms not just sine waves. 

--- End quote ---
That's true, and maximum sensitivity is normally about peak voltages, but absolute maximum voltages, similar to CAT ratings, are normally RMS. Look at the ratings of the more reputable scope vendors. Clearly as you've shown they deviate from this practice. But then I would take the absolute maximum ratings for these scopes with a bucket of salt anyway.


--- Quote from: wasedadoc on March 18, 2023, 11:40:50 pm ---Also my interpretation of the opening post is that the 230 v is not AC mains and the concepts of Live/Neutral or Phase/Ground etc may not apply.  The OP could clarify that.

--- End quote ---
An inverter will still produce single phase power, and I'd hope that for safety reasons one side is tied to ground inside the inverter. But more clarification would be really helpful indeed.

Saying things like don't connect anything to USB makes me worry, because to me that would mean touching the scope could shock you.
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