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Topic: BEGINNERS: Measuring voltages with a DMM, and staying alive! (Read 1 time) previous topic - next topic

lastchancename

Feb 12, 2020, 03:19 am Last Edit: Feb 12, 2020, 10:27 pm by lastchancename
Question copied from a thread on EEVblog by Serge 125
https://www.eevblog.com/forum/beginners/how-to-check-live-voltage-value-in-circuits-with-an-analogdigital-meter/new/

Quote
For as long as I can remember I would like learn how to check voltage on a live circuit but I've looked every where in books, vids etc.... for any detail on how to do this and I just can't find this. I remembering a long time ago I did poked on a live circuit and fried something and since then I have never poked on live circuit because I'm afraid to short something and make things worse. Mr EEVblog you have a MASSIVE vid collection on YT, but I don't know if you have one that explains how to check live voltage values on circuit boards
At a very fundamental level, any voltage you will measure is at a potential with reference to some other point of the circuit...

Usually 0V, or often that's tied to GROUND, but [WARNING] you can't guarantee that.

Consider that some voltages may be AC, so your readings, method and range of measurement will be different from DC measurements.

And finally, do your research on WHAT you're probing. mains-level voltages (AC or DC), can kill you in a dozen different ways.

... and a quick reminder. If your meter is set to a current range (A or mA), that presents virtually a short-circuit across the probes.  Don't forget, when measuring a voltage in the current ranges will usually fry your device or meter?
Experienced responders have a nose for laziness, (they were beginners once)... Sure, there are trolls, chest-beaters, and pretenders - but the help you'll get here is about as good as it gets - if you try to help youself!.

RIN67630

Mains voltage did not kill me.
But almost.

The devil did not want me.
Yet.

I am now enjoying my second life.
I have now a permanent scar at my hand where the current entered.
It went out along my feet passing through the heart line.


lastchancename

@RIN6730 welcome back to Earth (literally). Many of us have had 'small' mains shocks, but you were very lucky.

A sensitive photo of your 'scarf' may help to pass on the risk/severity to the kids and tinkerers here.   Glad you made it through.
Experienced responders have a nose for laziness, (they were beginners once)... Sure, there are trolls, chest-beaters, and pretenders - but the help you'll get here is about as good as it gets - if you try to help youself!.

RIN67630

@RIN6730 welcome back to Earth (literally). Many of us have had 'small' mains shocks, but you were very lucky.

A sensitive photo of your 'scarf' may help to pass on the risk/severity to the kids and tinkerers here.   Glad you made it through.
Twenty-five years after, my finger scar is not very spectacular any more:



It was just at the point where my finger did hold the plier at the end of the insulation.
I just could not unclasp the plier until I fell consciousless.
It was newertheless a third grade burning (painless, as all nerves are burnt).

lastchancename

Experienced responders have a nose for laziness, (they were beginners once)... Sure, there are trolls, chest-beaters, and pretenders - but the help you'll get here is about as good as it gets - if you try to help youself!.

lastchancename

#5
Feb 18, 2020, 09:09 am Last Edit: Feb 18, 2020, 09:11 am by lastchancename
@deepak, Not a bad example, but my meters don't have a mAVĪ© position... not many do.

Perhaps add some photos or diagrams (in-line)  to show the methods, and break up your paragraphs to be more readable, particularly as you introduce steps. This has to be extremely clear and simple for beginners.

You can update your first post since you're not changing anything.
+karma
Experienced responders have a nose for laziness, (they were beginners once)... Sure, there are trolls, chest-beaters, and pretenders - but the help you'll get here is about as good as it gets - if you try to help youself!.

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