How to check a 230VAC sine/modified wave with an oscilloscope (FNIRISI 1013D)

[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]

i will use it in battery mode, with connecting anything to USB port.

...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]

I'd expect 400V max to be 400V rms,

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]

I'd expect 400V max to be 400V rms,

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

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.

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.

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.

[juan3211]

Sorry, original post corrected.

So there is a new option: simple voltage dividir made with resistors. Thanks.
Do you think it will be better a transformer (I already have a little one) ?

i will use it in battery mode, with connecting anything to USB port.

...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.

[juan3211]

Thanks, so you proposal is use transformer and 10x probe.

Thanks a lot for your suggestions.

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.

[juan3211]

 
It is incredible.
 I haven't still recieved it but two different YouTubers have confirmed me that they have already measured 230VAC mains waves.

Thanks a lot for your information. When I receive the unit I will read manual and I hope read this. 

So no 10x probe measuring directly main's circuit. Thanks.

I'd expect 400V max to be 400V rms,

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.

[juan3211]

So if I want to check my home circuit (ground +neutral+phase, generally neutral is connected to ground in grid's substation) how do I need to connect transformer secondary outputs ? What is the correct option?

A. One transformer output to ch1, second output to ch2, main's ground to ground clips of the two channels. (Probably I will see one channel as a plain signal, as ground is connected to neutral)
B. One transformer output to ch1 and ground clip to the second output (it doesn't matter nuetral or phase).

And in a case of neutral+phase of an inverter ?
A. Like A, clips connected to home grid grounds
B. Only connect to transformer secondary outputs. Only one channel is used.

Could you help me? May be there is an better option C ?

Thanks.

I'd expect 400V max to be 400V rms,

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

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.

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.

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.

[nctnico]

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.

For as long as you clip the ground clip of the probe to ground (the actual ground!) you can use a 100x high voltage probe (with a CAT rating for mains voltages) to measure between ground and phase. If you want to measure between neutral and phase, then the only safe solution is to use a CAT rated, high voltage differential probe. The Fnirsi 1013D is not designed to be used as a floating / isolated oscilloscope. It does not provide the necessary isolation barrier to be safe to use / touch / operate even when running from it's internal batteries. Battery operated oscilloscopes are typically NOT suitable to measure dangerous voltages. Only when the models that have dedicated, high voltage CAT rated isolated inputs (IOW: a high voltage differential probe built in), they are safe to use on mains directly. The tell tale sign is the price; oscilloscopes with isolated inputs are very expensive (starting from ball park US $800).

[juan3211]

Thanks a lot
 
With all your suggestions, it is clear for me that I can't use the 1013D "directly".

I will use with a transformer.

What do you know about the options that I have proposed in my previous message ?  (A, B, ...C ?)

I already have a transformer, so I don't need to buy an expensive 100x probe or differential probe

The Fnirsi 1013D is not designed to be used as a floating / isolated oscilloscope. It does not provide the necessary isolation barrier to be safe to use / touch / operate even when running from it's internal batteries. Battery operated oscilloscopes are typically NOT suitable to measure dangerous voltages. Only when the models that have dedicated, high voltage CAT rated isolated inputs (IOW: a high voltage differential probe built in), they are safe to use on mains directly. The tell tale sign is the price; oscilloscopes with isolated inputs are very expensive (starting from ball park US $800).

[modoran]

Specs you linked are fake, already proven by various eevblog members. Do not trust what fnirsi says in their advertisements.

Yes, using a isolated transformer and measuring only secondary output will be fine ( except the signal amplitude, of course ).   But beware that not all "inverters" output sine waves, most of them don't.

[wasedadoc]

If you only want to determine the waveform shape you only need a few pieces of insulated wire. Wrap 10 cm of one around a wire from one pole of the inverter output  Likewise wrap another around a wire from the other pole. Connect the 10x probe tip to one of the wires - not an inverter output.  Likewise connect probe clip to the other wire.  There will be enough capacitive coupling between inverter output and probe to safely give a small signal to the scope.

If you need to know the effective amplitude use a true RMS voltmeter.

Most low price inverters give "modified sine wave".  Just a few discrete levels.  Fine for switch mode PSUs and purely resistive loads.  May not be good for 50/60Hz transformers, motors etc. Heed any such warnings in the inverter's user manual.

[WackyGerman]

In the manual you get all the information you need . You have to to prepare your own 100x probe for doing this measurement . Go to "http://www.fnirsi.cn/support" and then choose FNIRSI 1013 D English manual.pdf

[juan3211]

That is precisely what I want to check. Pure sine waves, or modify ones.

What about connection to the secondary of transformer?

Thanks

Specs you linked are fake, already proven by various eevblog members. Do not trust what fnirsi says in their advertisements.

Yes, using a isolated transformer and measuring only secondary output will be fine ( except the signal amplitude, of course ).   But beware that not all "inverters" output sine waves, most of them don't.

[juan3211]

Thanks this is a new option, but as I already have the transformer, how do I need to connect the secondary? Thanks

If you only want to determine the waveform shape you only need a few pieces of insulated wire. Wrap 10 cm of one around a wire from one pole of the inverter output  Likewise wrap another around a wire from the other pole. Connect the 10x probe tip to one of the wires - not an inverter output.  Likewise connect probe clip to the other wire.  There will be enough capacitive coupling between inverter output and probe to safely give a small signal to the scope.

If you need to know the effective amplitude use a true RMS voltmeter.

Most low price inverters give "modified sine wave".  Just a few discrete levels.  Fine for switch mode PSUs and purely resistive loads.  May not be good for 50/60Hz transformers, motors etc. Heed any such warnings in the inverter's user manual.

[juan3211]

This is the transformer what I have. Tyco

[wasedadoc]

In the manual you get all the information you need . You have to to prepare your own 100x probe for doing this measurement . Go to "http://www.fnirsi.cn/support" and then choose FNIRSI 1013 D English manual.pdf

I already attached a relevant extract from the manual in Reply #3.

[WackyGerman]

Oops , you`re right 

[Fungus]

That is precisely what I want to check. Pure sine waves, or modify ones.

What about connection to the secondary of transformer?

A transformer can change the shape of the wave. The most accurate way is with a 100x probe... or make a box with a resistor divider in it.

[juan3211]

Thanks a lot, here, in a previous post  I asked for this topic , but someone has ansemwer me that I could lost few armónicos but nothing about changing the shape.

So then the use of transformer is not an option for you, is it ?

I have changed the topic of the post to help.other with same question.

That is precisely what I want to check. Pure sine waves, or modify ones.

What about connection to the secondary of transformer?

A transformer can change the shape of the wave. The most accurate way is with a 100x probe... or make a box with a resistor divider in it.

[wasedadoc]

You will easily distinguish between pure and modified sine wave by just placing the scope probe tip close to an insulated cable from the inverter output.  No connection required.

Or two multimeters, one true RMS and one not.  (Most analogue meters are not).  If they read the same within meter tolerances it is pure sine.

[juan3211]

But as you know we always want more, and I want to see the curve and compare curves of different inverters, ....

You will easily distinguish between pure and modified sine wave by just placing the scope probe tip close to an insulated cable from the inverter output.  No connection required.

Or two multimeters, one true RMS and one not.  (Most analogue meters are not).  If they read the same within meter tolerances it is pure sine.

[juan3211]

Hi, what do you think is better ?
Make my own 10x divider with 10 X 1 Mohm resistors and use the 10x probe (total 100x, and I don't care of I measure 232 or 235 because of different values in resistors)

Or a transformer 230/48 and measure with 10x probe ?

I think I will use one of these options. What do you think?

I hope you understand that I don't want to buy an expensive 100x probe afte buying a cheap oscilloscope, and only for a few test.

[Fungus]

Hi, what do you think is better ?
Make my own 10x divider with 10 X 1 Mohm resistors and use the 10x probe (total 100x, and I don't care of I measure 232 or 235 because of different values in resistors)

I would use 200k resistors so your 'scope doesn't affect the circuit so much.

I hope you understand that I don't want to buy an expensive 100x probe afte buying a cheap oscilloscope, and only for a few test.

Just don't cheap out on the precautions. Be aware of polarities, etc. It might even be wise to measure across a resistor in the middle of the chain so there's always a megaohm or so between you and the electrons. Everything else should be in a box with just that one resistor exposed.

[juan3211]

Yes, I understand that. I can't touch, just in case, even the BNC connector of the probe without disconnecting the mains source in the circuit. I need to connect/touch everything before switching on the circuit.

May be anyone could share us her/his experience.

Thanks for yours.

Hi, what do you think is better ?
Make my own 10x divider with 10 X 1 Mohm resistors and use the 10x probe (total 100x, and I don't care of I measure 232 or 235 because of different values in resistors)

I would use 200k resistors so your 'scope doesn't affect the circuit so much.

I hope you understand that I don't want to buy an expensive 100x probe afte buying a cheap oscilloscope, and only for a few test.

Just don't cheap out on the precautions. Be aware of polarities, etc. It might even be wise to measure across a resistor in the middle of the chain so there's always a megaohm or so between you and the electrons. Everything else should be in a box with just that one resistor exposed.

[Fungus]

Yes, I understand that. I can't touch, just in case, even the BNC connector of the probe without disconnecting the mains source in the circuit. I need to connect/touch everything before switching on the circuit.

If you're measuring a resistor in the middle of the resistor chain then no matter how you connect things there's still a megaohm or so between you and the real power. Max current will be lass than a milliamp.

[juan3211]

What about P4100 100:1 probe ?

https://a.aliexpress.com/_EHZzXD5

May be the best option is a "small transformer block to step-down to a safe voltage" method? does it disturb signals?

[wasedadoc]

Depending on your definition of "small" I can confirm from my own practical observations that what Fungus already wrote that transformers can distort the waveform is true.  However if you are merely interested in sine versus multilevel approximation and if the latter seeing how many levels, then any of the several methods already suggested to you would have had the job done days ago.

[adam4521]

I understand earlier in the thread we do not know whether the inverters will be earth referenced, neutral referenced (if UPS), or floating.

That being the case the most flexible and safe ‘low cost’ measurement is to use the transformer method. The wave ‘shape’ on the secondary will be close enough to the primary.

Agree with everyone — get the live conductors into an enclosure. OP, if that is too much hassle you might find you already have an enclosed plug-top transformer in your house, like this one I kept from an old Netgear router. While AC-AC transformers are not common for new kit now, you can still find inexpensive ones sold in a case as ‘doorbell transformers’.

I would test your inverter output with a small resistive load (eg tungsten desk lamp) to get some current flowing.

[Zero999]

That is precisely what I want to check. Pure sine waves, or modify ones.

What about connection to the secondary of transformer?

A transformer can change the shape of the wave. The most accurate way is with a 100x probe... or make a box with a resistor divider in it.

Yes a transformer will distort this signal a little, but not enough to be visible on an oscilloscope at mains frequencies, you'll still be able to distinguish between a modified and pure sine wave. Most of the distortion will occur at higher frequencies, so there might be some ringing on the modified sine, but it should be fairly obivous.

[juan3211]

Even for compare several "pure" sine waves between them, or several modified sine waves between them ?

Do you think tha transformer will not modify enough the waves? May be only a very high frequencies?

Thanks.

That is precisely what I want to check. Pure sine waves, or modify ones.

What about connection to the secondary of transformer?

A transformer can change the shape of the wave. The most accurate way is with a 100x probe... or make a box with a resistor divider in it.

Yes a transformer will distort this signal a little, but not enough to be visible on an oscilloscope at mains frequencies, you'll still be able to distinguish between a modified and pure sine wave. Most of the distortion will occur at higher frequencies, so there might be some ringing on the modified sine, but it should be fairly obivous.

[tggzzz]

Even for compare several "pure" sine waves between them, or several modified sine waves between them ?

Do you think tha transformer will not modify enough the waves? May be only a very high frequencies?

You have to define what "compare" and "modify enough" means. That implies you have to define your objectives.

Other snippets from your posts....

I haven't still recieved it but two different YouTubers have confirmed me that they have already measured 230VAC mains waves.

Youtubers also confirm the world is flat, that 5G causes cancer, and that the world is run by giant reptiles living under a mountain.

Given that, what's your point again?

That is precisely what I want to check. Pure sine waves, or modify ones.

As others have stated, to check that you don't need to make a physical connection - just hold a probe near the output and capacitive coupling will show you enough to distinguish that.

So if I want to check my home circuit (ground +neutral+phase, generally neutral is connected to ground in grid's substation) how do I need to connect transformer secondary outputs ? What is the correct option?

The correct option is to read and understand the references in https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/ There are many obvious and subtle ways in which a beginner or experienced professional can damage themselves or scope or UUT.

[juan3211]

Thanks a lot. I must admit that my posts are not clear enough.

Now I know that these two YouTubers how review the 1013D don't know a lot about it or about electronics in general.


I want to test several inverters and signals. All 230VAC RMS.
My goal is to check if it is pure sine or not, and this is very easy.

But also, I am asking myself if there are also differences among pure sine waves , and among modified sine waves.

I am sure that they are.

The Fnirisi 1013D has a FFT (Fourier) to see harmonics of a signal, and may be I could compare this data among pure sine to see the quality of them. Probably main's harmonics will be different than an cheap Chinese inverter.

I dont need to compare them with high detail, but yes basics.

May be I have explained (with my words) better.

Thanks a lot guys!
 

[wasedadoc]

You are overthinking this.  Just get started by holding the probe near an insulated output from the inverter.  No connection needed.  There is a good chance that will tell you all you want to know.  If not, you can proceed to a more advanced method.

[joeqsmith]

...
Now I know that these two YouTubers how review the 1013D don't know a lot about it or about electronics in general.
...

Rather than place the blame on the YouTubers,  maybe consider the SISO factor (Shit In = Shit Out).   Asking better questions may yield better results.

DDS (DIY Domótica Solar) 21 hours ago
​@joe smith  hi , in order to measure a 50-60hz sine wave to check some inverters, main grid,... modified or pure sine, armonics, .... Is it good to use a step down transformer ? For example, from 240vac to 24vac. Or it (transformer) will distrub, smooth, .... signal ?

joe smith13 hours ago
 @DDS (DIY Domótica Solar)  It depends what you are after.   Anything you use will cause some error.   Not all transformers will have the same response.  Of course, you don't want to apply any DC to a transformer.  Following videos show a simple transformer / LEM used to measure AC power with my scope. 

[tggzzz]

Asking better questions may yield better results.

Just so.

General truism: it is easy to answer a question correctly, but it is more difficult to know the correct question to ask.

[JeremyC]

I want to test several inverters and signals. All 230VAC RMS.
My goal is to check if it is pure sine or not, and this is very easy.

But also, I am asking myself if there are also differences among pure sine waves , and among modified sine waves.

juan3211, keep in mind that 230V RMS = 650Vpp. You should buy a high voltage differential probe like the Miscig DP10013.
Sample link:  https://www.amazon.com/Micsig-DP10013-Differential-Attenuation-Tektronix/dp/B074K4XPW3

[shapirus]

high voltage differential probe

High voltage yes, but it doesn't have to be differential. Inverters are floating, because they are battery-powered. They don't have any connection to ground.

[JeremyC]

high voltage differential probe

High voltage yes, but it doesn't have to be differential. Inverters are floating, because they are battery-powered. They don't have any connection to ground.

OP mentioned that he may need to check mains in his house

So if I want to check my home circuit (ground +neutral+phase, generally neutral is connected to ground in grid's substation) how do I need to connect transformer secondary outputs ? What is the correct option?

[juan3211]

Thanks, he is my brother in law, I am helping him by posting here. I will check the videos myself and try to explain him, thanks

[juan3211]

Yes, that is why the best option could be a simple step down transformer. As I have read all of you, it will not disturb the wave form a lot, so for a no-precise job, it may work

high voltage differential probe

High voltage yes, but it doesn't have to be differential. Inverters are floating, because they are battery-powered. They don't have any connection to ground.

OP mentioned that he may need to check mains in his house

So if I want to check my home circuit (ground +neutral+phase, generally neutral is connected to ground in grid's substation) how do I need to connect transformer secondary outputs ? What is the correct option?

[joeqsmith]

Thanks, he is my brother in law, I am helping him by posting here. I will check the videos myself and try to explain him, thanks

...
Now I know that these two YouTubers how review the 1013D don't know a lot about it or about electronics in general.
...

Rather than place the blame on the YouTubers,  maybe consider the SISO factor (Shit In = Shit Out).   Asking better questions may yield better results.

You posted the comment blaming YouTubers, not your brother in law.  Now you blame him.   I may not know a lot about electronics in general but I'm mature enough not to blame others for my shortcomings. 

[juan3211]

Sorry, I am not speaking about you. I was speaking a out two YouTubers that said that the Fnirisi 1013d was capable of measuring 230vac with 10x and that they already had done it.

Sorry if have written something that you feel bad.

Sorry.

Of course it is not general, I am more confident with this forum, not YouTube. My brother in law has get that answer from 2 YouTubers. NOT YOU

Sorry again for misunderstanding.

Thanks a lot for all your help.

Thanks, he is my brother in law, I am helping him by posting here. I will check the videos myself and try to explain him, thanks

...
Now I know that these two YouTubers how review the 1013D don't know a lot about it or about electronics in general.
...

Rather than place the blame on the YouTubers,  maybe consider the SISO factor (Shit In = Shit Out).   Asking better questions may yield better results.

You posted the comment blaming YouTubers, not your brother in law.  Now you blame him.   I may not know a lot about electronics in general but I'm mature enough not to blame others for my shortcomings.

[juan3211]

Thanks a lot for your videos.

They are quite complicated for me, but this is my fault, not yours. I am newbie. I can see that you measure the wave form after a transformer with little distortion in it.

As I understand, in this videos you are not comparing the wave before and after the transformer, are you?  I have tried to searched a video with this comparation but I can not find anything similar.

Anyway, thanks a lot. I think that I can go on using an step down transformer

Thanks a lot guy and sorry again for my words, I didn't want to create polemic.

...
Now I know that these two YouTubers how review the 1013D don't know a lot about it or about electronics in general.
...

Rather than place the blame on the YouTubers,  maybe consider the SISO factor (Shit In = Shit Out).   Asking better questions may yield better results.

DDS (DIY Domótica Solar) 21 hours ago
​@joe smith  hi , in order to measure a 50-60hz sine wave to check some inverters, main grid,... modified or pure sine, armonics, .... Is it good to use a step down transformer ? For example, from 240vac to 24vac. Or it (transformer) will distrub, smooth, .... signal ?

joe smith13 hours ago
 @DDS (DIY Domótica Solar)  It depends what you are after.   Anything you use will cause some error.   Not all transformers will have the same response.  Of course, you don't want to apply any DC to a transformer.  Following videos show a simple transformer / LEM used to measure AC power with my scope. 

[joeqsmith]

..They are quite complicated for me, but this is my fault, not yours. I am newbie. I can see that you measure the wave form after a transformer with little distortion in it.

As I understand, in this videos you are not comparing the wave before and after the transformer, are you?  I have tried to searched a video with this comparation but I can not find anything similar.
..

Unlike you, I provided a plethora of information about my goals.   I mentioned what I showed was just for fun.  I based my criteria from IEC 6100-3-2 which calls for 40 harmonics.  Living in the USA, I used a fundamental of 60Hz,  or 2400Hz for the upper end.  To improve my scope's limited vertical resolution, I set the sample rate (after filtering and decimation), of 3X over the 40th harmonic (7200Hz). 

I stated that ANY measurement will have errors and that transformers are not all the same.   I've shown using/designing transformers well into the MHz on this forum.  I mentioned that I had no idea what that transformer I used for these two videos was.  It is very old and possible an audio transformer from a tube amplifiers.   To get some idea of how it behaved I swept it from 10Hz to 200KHz and we were not close to the 3dB point.   I then overlaid the primary and secondary along with the LEM at 100kHz using basically a resistive load (PF=1).  It was far beyond what I needed to meet my goals.   

You shouldn't expect what ever E core you find to yield the same results.  Still if you needed to measure MHz on your AC mains, I made a few videos walking through the calculations for a couple of diff probes I cobbled together.   With diff probes being so cheap, it's nothing I would recommend building.   

[Zero999]

I haven't read the entire thread in detail. It's now too long and filled with fluff it's completely unreasonable to expect anyone to read thoroughly.

Briefly: yes it's possible to measure the mains with a standard x10 probe, if the neutral is connected to mains earth. Just connect the probe to the phase conductor and it will work. Obviously don't connect the neutral of the grid to earth, as the only the distributor is allowed to do that. In the case of an inverter: check the resistance with a multimeter, when it's connected up, but switched off. It's generally a good idea to earth the neutral of an inverter to prevent it from floating at high voltages. Read the manual. If in doubt, use two x10 probes: one on the live and the other on the neutral and the math/differential function.

As mentioned above, a small mains transformer is also a decent option. It won't introduce any noticeable distortion on a pure sine wave, but perhaps a little on the modified sine wave. A toroidal transformer is better. I've found small mains transformers are generally good up to 10kHz, but obviously the losses will be higher with increasing frequency. I'm purely referring to using one for voltage measurement, but to power anything.

[juan3211]

Thanks a lot for this answer !

I haven't read the entire thread in detail. It's now too long and filled with fluff it's completely unreasonable to expect anyone to read thoroughly.

Briefly: yes it's possible to measure the mains with a standard x10 probe, if the neutral is connected to mains earth. Just connect the probe to the phase conductor and it will work. Obviously don't connect the neutral of the grid to earth, as the only the distributor is allowed to do that. In the case of an inverter: check the resistance with a multimeter, when it's connected up, but switched off. It's generally a good idea to earth the neutral of an inverter to prevent it from floating at high voltages. Read the manual. If in doubt, use two x10 probes: one on the live and the other on the neutral and the math/differential function.

As mentioned above, a small mains transformer is also a decent option. It won't introduce any noticeable distortion on a pure sine wave, but perhaps a little on the modified sine wave. A toroidal transformer is better. I've found small mains transformers are generally good up to 10kHz, but obviously the losses will be higher with increasing frequency. I'm purely referring to using one for voltage measurement, but to power anything.