Hi guys, as far as i know, light dimmer produces harmonic distortions
to the main supply. In order to check the distorted waveform which
contains many levels of harmonics, where should I check the output? I
mean is if i want to use an oscilloscope to capture the image of the
distorted waveform, where should I put the probe of the oscilloscope.


Hope you guys can help me. Thanks.

"ooi_yw" writes:

Hi guys, as far as i know, light dimmer produces harmonic distortions
to the main supply. In order to check the distorted waveform which
contains many levels of harmonics, where should I check the output? I
mean is if i want to use an oscilloscope to capture the image of the
distorted waveform, where should I put the probe of the oscilloscope.

Putting the scope on the Hot before the dimmer will get you started.
if I understand what you want to do.

But what you probably really want is A-B between the Hot before the dimmer
and the Neutral used by the load.

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If you want to see the distorted current through the light bulb, put a
1 ohm resistor between the "ground" side of the light bulb and the
ground lead. Then put the oscilloscope probe on the hot side of the 1
ohm resistor. That way you do not need an A-B scope input.

Just make sure the "ground" side of the light fixture and the ground
through the scope probe of the scope and the ground of the chassis of
the oscilloscope are all at the same potential before you do this.

H. R.(Bob) Hofmann

wrote:
If you want to see the distorted current through the light bulb, put a
1 ohm resistor between the "ground" side of the light bulb and the
ground lead. Then put the oscilloscope probe on the hot side of the 1
ohm resistor. That way you do not need an A-B scope input.

Just make sure the "ground" side of the light fixture and the ground
through the scope probe of the scope and the ground of the chassis of
the oscilloscope are all at the same potential before you do this.

H. R.(Bob) Hofmann



I would *highly* recommend using an isolation transformer for this, pick
up a light dimmer and wire it up with a lightbulb on the bench from the
isolated supply, then scope it.