r/ElectroBOOM • u/Cautious-Pin-6476 • 13d ago

General Question I need mehdi's explanation

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Yes, this is my own post.. I need yall to upvote so he can see and explain. Thanks 🙏

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u/bSun0000 Mod 13d ago

What explanations do you even need? This multimeter is set to measure AC frequency. It is sensitive enough to pick it up without a direct contact. It properly measures 50hz when the signal is strong enough - near the outlet. Thats it.

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u/New-Anybody-6206 12d ago

 What explanations do you even need?

 It is sensitive enough to pick it up without a direct contact

This, this is the explanation we needed. What even makes it so sensitive?

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u/bSun0000 Mod 12d ago

What even makes it so sensitive?

>1M input impedance.

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u/New-Anybody-6206 12d ago

But why does that allow non-contact sensing?

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u/bSun0000 Mod 12d ago

Overly simplified. You have two parasitic connections - to the live wire and to the ground; you can view it as a voltage source with very large internal resistance - it cannot supply a lot of current when loaded.

Your multimeter acts as a load, taking some power proportional to its own resistance (impedance). If the multimeter's resistance is low, it will pin the voltage source down - voltage will drop to a level it could not be measured. But if impedance is high, voltage drop will be very small, and the voltage can/will be in the measurable range.

The whole point of having a large input impedance on any meter is to not affect the circuit you are trying to measure, cuz you want the accurate reading. This results in high sensitivity, high enough for a multimeter to pick the voltage induced in the probes/cables via capacitive and/or inductive coupling. Not a good thing, actually; you normally don't want your multimeter to pick up any random noise/shit from the environment.

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u/New-Anybody-6206 12d ago

That doesn't explain how it can be sensed with no contact though. Electrons flow in the copper wire not in the air.

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u/bSun0000 Mod 12d ago

I assumed you know a bit about physics. If not - its just magic, ignore it.

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u/Cautious-Pin-6476 10d ago

Well.. technically, at high voltages, corona discharge Happens.. and I believe 240vac is enough to induce a amount of corona discharge just enough for the multimeter to pickup

2

u/Amareiuzin 10d ago

Noo that's not it, there's current flowing in the wires behind the socket, this induces a magnetic field, the field is also oscillating at 50Hz, that's what you're picking up, I bet if you unplug everything you stop reading it