Electronics > Beginners
Would this work as an AC probe?
(1/5) > >>
Beamin:
Say I wanted to probe the outlet with my oscilloscope. What if I took a small toroid ran 10 turns of magnet wire down one side and ten turns on the other, two conductors four contacts: hot and neutral in, and 2 AC outs. The AC line side 120VAC would have a 1 mohm resister on it. That would create 0.12mA of current flowing through and not get hot and pass at most 14mW?  The scope impedance would be set to what? It has a 50ohm setting or other settings (can't make out the other right now it's a tek 2465) . That always gets me is that 50 ohms like my 50 ohm inductance like a coax cable or is it 50 ohms electrical resistance? The circuit would be sealed in a small box with silicone like ghetto potting and care would be used (I use latex gloves when ever I work with AC {anything >12volts} or charged caps) handling the output wires.
I always consult the internet when working with high voltage or break my most valuable equipment.
That's all A/C coupling is right? Or is that when they use a cap to filter out the DC?
tooki:
I don’t even know enough about magnetics to call myself a beginner, but 10 turns of magnet wire will just be a fuse and burn up. Why not buy an off the shelf 120V->12V transformer and just probe the output of that?
Beamin:

--- Quote from: tooki on October 15, 2018, 12:24:53 am ---I don’t even know enough about magnetics to call myself a beginner, but 10 turns of magnet wire will just be a fuse and burn up. Why not buy an off the shelf 120V->12V transformer and just probe the output of that?

--- End quote ---

I have parts on hand and ordering transformers takes a long time.  Ohms law says it shouldn't blow up at those ohm/voltages. You should be able to put a 1 mohm across the outlet unless I mixed up the decimal place.
PointyOintment:
Putting 1 milliohm across an outlet (assuming 120 V) will result in a current of 120 kA. I doubt your circuit breaker will allow that.
vk6zgo:
Well it is fairly obviously  mistyping by Beamin, as the value of 0.12mA works out correctly for 1Megohm.
My understanding is that the resistor will be in series with the transformer primary.

The problem I can see is that a transformer using a random toroid may not be very useful at 60 Hz.
Even if it works, it may not represent a true version of the input waveform.

The error may be worse than just probing the "hot" side of the Mains with no ground clip connection,
using the long connection back through the PE lead of the 'scope, the house wiring back to the PE/Neutral
connection & back again to the test point Neutral.

Another way of looking at the Mains waveform is to use the " Pseudo differential " connection, using two vertical channels, & the A+B vertical function.

You say you would need to order a transformer to observe the AC Mains waveform at its secondary, but you may be surprised how many transformers may be around the place.

Old "wall warts" used transformers, some, indeed, have AC output.
Even if you have to "open one up", bypass the rectifiers, & glue it back together, you have the advantage of a commercially made transformer.

How about your soldering iron?
Some feed low voltage AC to the heater, normally from a transformer.
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod