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Oscilloscope Connection Question

jedro

Dec 1, 2014
6
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Dec 1, 2014
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If I want to see wall outlet voltage and wave form, is connecting the probe as per the attached illustration correct? New oscilloscope. Don't want to damage it.

Yes. I know to be careful. Thanks.

 

Nanren888

Nov 8, 2015
623
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Nov 8, 2015
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623
Damage?
It depends on whether the probe and scope can handle the voltage.
Check the specs of the probe and scope.
If you are having to ask, I'd have to suggest that you not do things with the mains power.
What's your reason for wanting to look at the mains?
Maybe there is another way to get what you want.
 

Externet

Aug 24, 2009
839
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Aug 24, 2009
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839
Much better to use a transformer that can be canibalized from a wall adapter and connect the oscilloscope to its secondary. Amplitude reading will be scaled down, frequency and waveform kept same.
 

Martaine2005

May 12, 2015
4,351
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May 12, 2015
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4,351
An isolation transformer is used or the usual expensive differential probes.
A dual scope with ‘add’ can be used but never use the GND clip.
I don’t think you should try try this with your new scope.

Martin

Martin
 

WHONOES

May 20, 2017
1,215
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May 20, 2017
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1,215
For safety's sake, I would go the isolating transformer route. I doesn't have to be big, 1VA type would be adequate, but what ever you have around (if any) would suffice.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
4,761
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Messin' with electrical power, provided with the full faith and credit of your electric utility, can lead to dire consequences for the uneducated and/or the inexperienced. Think of the words "short circuit" and up to 10,000 amperes short-circuit current before a circuit breaker opens. Only use the GND lead of the o'scope probe to connect to circuit ground of circuits isolated from the mains galvanically. If you don't know what that means, don't connect the o'scope GND lead at all. Most modern o'scopes use the "three prong" convenience plug, and the "ground" of this plug is connected to the GND lead of the o'scope probe, sometimes with some small series resistance (for whatever reason). Point is, you don't NEED to connect the o'scope GND lead at all! It is already connected to "earth ground" as soon as the o'scope is plugged into the convenience outlet.

In the USA, the neutral-hot-ground terminals on a convenience receptacle may be, and often are in older installations, connected incorrectly. Typically, the "neutral" and "hot" connections are reversed. This causes problems if you expect the neutral wire to be near "ground" potential. The "D-shaped" terminal on the convenience receptacle should (eventually) be connected to the earth ground rod at the service entrance. It will also be connected to "neutral" at the distribution panel, and only at the distribution panel (where the circuit breakers are mounted). Depending on the amount of current in the "neutral" wire, which should be the same as the amount of current in the "hot" wire, there may be a small voltage drop between "neutral" and "ground" on the receptacle, caused by the IR drop in the "neutral" wire.

Please tell us WHY you want to probe live outlets with your o'scope. There ARE legitimate reasons to do so, and SAFE ways to perform the measurements, but you obviously need some help to learn how and when to make such measurements. A small step-down "filament" transformer is the safest way to monitor the amplitude and waveform of the AC line. Typically these "step down" the line voltage to about 6.3 VAC. You might want to do this to verify that a DC to AC inverter is performing properly under load.
 
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