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Measure mains (230V) with osciloscope
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mitrynicolae:
Hello everyone,

I have a simple yet complicated question (at least for me). How do I safely visualize with an oscilloscope the mains voltage? I have this scope https://www.linkinstruments.com/mso19.htm and the 1x/10x probe. Now there are multiple questions for which I still don't have a clear answer.
 - if the osciloscope with the 10x probe can only support 40v then this means that I need a 100x probe in order not broke the scope?
 - in the video #279 Dave Jones presented some ways in which beginner electronics hobbyists can blow up their scopes. Is there any setup, in which I could hook up the probe that could result in destruction of the scope or me being electrocuted?
 - can there be an issue if I put the ground lead to the live wire and the probe tip to the neutral?

To understand what I am trying to achive, I have this stabilizer: https://www.emag.ro/stabilizator-electronic-de-tensiune-electropower-ep-jjw-15kva-cp-jjw-15kva/pd/DW7WSYBBM/ and the producer claims that the stabilizer has a sinusoidal output. More over they claim that the output has 1% accuracy and a response time of 100ms. The issue is that when my home boiler (similar to this one http://www.ariston.com/uk/Wall-Hung_Boilers_Combi/clasnetone) starts up there is a huge voltage spike that eventually leads to an over voltage protection to shut down the mains in the entire home. If I gradually start the appliances in the house then there is no issue and the stabilizer work as it should, but if for some reason the mains was absent and then come back the spike in the stabilizer leads to shut down the mains to the entire home, As you can imagine the whole system enters in a loop from which is hard to recover and that could lead to some devices to blow up.

Thank you for your time!
george.b:

--- Quote from: mitrynicolae on November 18, 2018, 03:08:04 pm --- - if the osciloscope with the 10x probe can only support 40v then this means that I need a 100x probe in order not broke the scope?
 - in the video #279 Dave Jones presented some ways in which beginner electronics hobbyists can blow up their scopes. Is there any setup, in which I could hook up the probe that could result in destruction of the scope or me being electrocuted?
 - can there be an issue if I put the ground lead to the live wire and the probe tip to the neutral?

--- End quote ---

1. Correct.
2. See next point.
3. Yes. If your scope is grounded (it should be), you'll short out the mains through the oscilloscope.

What I would do if I were you would be to measure the mains waveform through a transformer, say, 230V/12V. Whatever happens on the primary will show up on the secondary, the oscilloscope will be isolated and you won't have to deal with higher voltages.
Benta:
The correct way of doing this is to use a differential probe, but they are pricey.
George.b's suggestion on using a transformer is cheap, easy and good enough for this test.
madires:
If you have two 100x probes you could also use the hobbyist's differential probe setup (remove ground clips, CH1 + CH2 inverted). Proper differential probes aren't cheap, but less expensive than a funeral. ;)
tggzzz:

--- Quote from: mitrynicolae on November 18, 2018, 03:08:04 pm ---Is there any setup, in which I could hook up the probe that could result in destruction of the scope or me being electrocuted?

--- End quote ---

Yes, many many ways, some obvious, some subtle - even when you take precautions. From a post 3 days ago: https://www.eevblog.com/forum/testgear/ground-of-oscilloscope-always-connected-to-earth/msg1967150/#msg1967150

It is good that you know what you don't know, and do ask questions. There are many answers on this forum, or at https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/
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