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Osciloscope noise on low voltages
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tggzzz:

--- Quote from: andyB2022 on December 18, 2022, 01:10:23 pm ---My house has no earth system and nothing can be done right now to change that. I do electronics mostly for testing and because it's a hobby.

--- End quote ---

"Earth" is a misleading term, for several reasons.

The mains lead has an earth connection.
That connection connects to a contact in the mains socket on your wall.
Is there a wire on that socket?
Where does that wire go?

There are various "protective mains earth" connection systems in use around the world. I am not an electrician and do not understand the details. The "earth" wire in a mains socket is unlikely to connect to the dirt that supports your house (for want of a better description!). Nonetheless, if connected appropriately, that earth wire can provide a useful function.
Fungus:

--- Quote from: tggzzz on December 18, 2022, 01:24:58 pm ---The "earth" wire in a mains socket is unlikely to connect to the dirt that supports your house (for want of a better description!).

--- End quote ---

I wouldn't say it's "unlikely" - they very often do.
tggzzz:

--- Quote from: Fungus on December 18, 2022, 01:53:31 pm ---
--- Quote from: tggzzz on December 18, 2022, 01:24:58 pm ---The "earth" wire in a mains socket is unlikely to connect to the dirt that supports your house (for want of a better description!).

--- End quote ---

I wouldn't say it's "unlikely" - they very often do.

--- End quote ---

Accepted, but how indirectly and in Romaina and where the OP believes it is not connected at all?
joeqsmith:

--- Quote from: andyB2022 on December 17, 2022, 02:09:33 pm ---Hi, I'm trying to measure with my Rigol DS1054Z the inrush current of various electronics using a Chinese 100A / 100mV shunt. The only problem that I have is that the noise is terrible and blinds away the important measurement. If I short the prode with the GND clip, the noise is gone, if I leave all four channels disconnected, noise is gone, most of the noise is 50Hz mains...

...

Thank you!

--- End quote ---

Depending on your requirements, you could amplify the signal across the shunt to get above the scopes noise floor.  Video below shows an old 100A shunt that was given to me.  You can see my chopper amplifier towards the end.   If you are only planning to measure lower currents, you could pick a different value shunt to increase the signal.    You may also consider using a different sensor than a shunt.   I have a few LEM sensors that can be used to 10s of kHz and several amps.  The nice thing about using a clamp, you have no need to float the scope or be concerned about where you are probing. 

andyB2022:

--- Quote from: tggzzz on December 18, 2022, 01:24:58 pm ---The "earth" wire in a mains socket is unlikely to connect to the dirt that supports your house (for want of a better description!).

--- End quote ---

Yes in Romania the Earthing of a house / building is done in two main ways, one of them is connection that 3rd connector (represented only by Green-Yellow colors) to "dirt" and to Neutral of the system. We have here TN-C-S system.


--- Quote from: joeqsmith on December 18, 2022, 04:36:44 pm ---Depending on your requirements, you could amplify the signal across the shunt to get above the scopes noise floor.  Video below shows an old 100A shunt that was given to me.  You can see my chopper amplifier towards the end.   

--- End quote ---

Thank you for the info, I'm interested in measuring Inrush currents most of the time with the shunt (most of the time in AC side). A current clamp would be lovely but everything comes at cost... And I doubt there is a clamp that can catch inrush transients as fast as a direct voltage drop across a resistor / shunt.
I'll look into your solution.
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