Connect probe properly for meassure 230vac with oscilloscope

Thread Starter

perik123

Joined Nov 9, 2019
7
I just got this combined multimeter - oscilloscope Hantek 2D72 In the specs it says:

Input: Maximum Input Voltage 150VRM

My probe specs are: Max Input voltage: 1X 150V rms cat II 10X 300V rms cat II
I want to meassure a dmx controlled dimmer. The output of the dimmer is 230 vac so I will use the settings for 10x. Since I havnt used oscilloscope before I wounder how can I connect the probe to the outlet?

Can I simply connect the probetip to the outlet like on this image (not my image) and the groundtip to the metallchassi for grounding?
L05Rc.jpg
 

Delta Prime

Joined Nov 15, 2019
1,190
Hello there. :)
using a 10:1 should show the AC fine but RMS is 240 V so peak will be 240 V x root 2 (1.414) so closer to 320-340 I believe (which on 10:1 probe will be -34 V to +34 V showing up on the scope) the more dangerous part of all this is to ensure proper grounding and measurement technique? how you plan to place your ground lead and especially if using both channels... since they share the ground back to common earth, I would highly recommend a differential probe.;)
 

DickCappels

Joined Aug 21, 2008
7,979
The way I do it. and I don't do this very often because I don't like messing with 240 VAC.

Using two 10X probes measure the line and neutral using the same vertical sensitivity for both channels. The ground clips should go to earth ground.

Set the scope to (Channel 1) - (Channel 2).

You now see the difference in voltage between the line and neutral, which is what your lamp will see.

Please, when probing voltages like this keep one hand in your back pocket or otherwise free of contact with any ground or conductor.
 

olphart

Joined Sep 22, 2012
99
The way I do it. and I don't do this very often because I don't like messing with 240 VAC.

Using two 10X probes measure the line and neutral using the same vertical sensitivity for both channels. The ground clips should go to earth ground.

Set the scope to (Channel 1) - (Channel 2).

You now see the difference in voltage between the line and neutral, which is what your lamp will see.

Please, when probing voltages like this keep one hand in your back pocket or otherwise free of contact with any ground or conductor.
I'd also look up the input impedance of the o'scope and use series resistors on both probes of at least 1/2 that value.
It'll still poke you pretty good if you make a handling error, but without damage.
I'll suggest a voltage divider to knock down the 240V to say ~24V. Still see waveform, but inherently safe.
 

Thread Starter

perik123

Joined Nov 9, 2019
7
Say I have a transformer taking the ac voltage down say from 230 vac to 12 vac. Would that be a good option. Still letting me see the waveform but in a safe way?
 

DickCappels

Joined Aug 21, 2008
7,979
The idea of a transformer is a great one in that it can provide excellent isolation. It has been done successfully for some instrumentation and control applicatins but whether or not it is right for your application depends on how much distortion you can tolerate. Transformers induce harmonic distortion.

1632680849928.png
Above: 50 Hz sine wave on the unloaded secondary of a transformer with a little harmonic distortion (left) and the spectrum of that sine wave Vertical is 10 db/division (50 Hz is 0 db, the 2nd harmonic is -26db, etc.)

Your transformer might give more of less distortion.
 

ronsimpson

Joined Oct 7, 2019
1,651
If money is noting, I have 100:1 probes for measuring higher voltage. Many 10:1 probes are not rated for power line voltages.
I also have 1000:1 and 10,000:1 probes when the voltage is very high.
I hate seeing people looking at the power line with a scope because they some time connect the ground clip wrong. I have ground clips damaged by connecting to something not at ground. (yes I have done it wrong to)
I also have floating probes or isolated probes where the ground clip is not connected to earth ground.
Another way to see the power line safely is to use a battery powered scope. I have one that is built to rid on the power line. It is built to be 2000 volts off of ground.
If money is noting, lol
 
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