Electronics > Beginners

Oscilloscope Mains AC Sinewave Testing

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The Electrician:

--- Quote from: n5yzv on September 12, 2019, 02:47:12 pm ---Here is the transformer:
https://www.amazon.com/gp/product/B076KX33JW/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

and please see the attached image:

--- End quote ---

I see that the problem is just as I suspected.  The giveaway is its description as an "Electronic" transformer with an "operating frequency = 20 kHz".  It's really a switching convertor.

If you get one of these: https://www.amazon.com/Parts-Express-Power-Transformer-6-3V-0-6-3V/dp/B0002ZPHLA/ref=sxbs_sxwds-stvp?keywords=power+transformer&pd_rd_i=B0002ZPHLA&pd_rd_r=56d27888-dc59-4dc6-9dfc-a9daf612d8d9&pd_rd_w=lVuxx&pd_rd_wg=vyQbP&pf_rd_p=a6d018ad-f20b-46c9-8920-433972c7d9b7&pf_rd_r=5J5M3W18FPPVH8NFYCCX&qid=1568301639

or:

https://www.amazon.com/Jameco-Valuepro-P-8657-R-Power-Transformer/dp/B00B88632C/ref=sr_1_247?keywords=power+transformer&qid=1568301878&sr=8-247

you will see a clean version of the grid waveform, and have the safety of a galvanically isolated connection to the grid.

The Electrician:
Zero999's explanation of the flat-topping is right on.  The distortions in grid waveform are various.  Here are some waveforms I captured some time ago in the Puget Sound region:





n5yzv:
Thank you!  I had no clue which one to get.  Is there a way to monitor AC mains over a time period and replay?   Again, using Rigol DS1054Z with all licenses.

The Electrician:

--- Quote from: n5yzv on September 12, 2019, 04:13:47 pm ---Thank you!  I had no clue which one to get.  Is there a way to monitor AC mains over a time period and replay?   Again, using Rigol DS1054Z with all licenses.

--- End quote ---

Set your scope to display a full cycle of the waveform, normal triggering, and then set the display to infinite persistence.  Any large deviations from the normal waveforms would show up.

Otherwise, to capture hours worth of waveform would require a lot of memory.  :)

scatterandfocus:
I'm interested in this topic too.  I tend to get some sporadic power noise in my audio recording chain.  Should it be ok to drop the voltage down to around 1V using a transformer and voltage divider and capture the output with a soundcard?

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