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Cheap Mains harmonics tester

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Why not verify the accuracy with a known signal spectrum (e.g. square wave from a signal generator)?

I would expect sufficient performance for pre-compliance measurements. As long as you are not dealing with non-harmonic or time varying signals, even the FFT window parameters shouldn't affect the results.
 
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Hi
This is a continuation of this thread if i may which is closed...

**broken link removed**

Has anyone tried to do mains harmonics measurements with eg picoscope 2205A?

Our contractor is telling us we must hire out a power analyzer at a cost of £150 for two days.
We only need a fairly rough indication of what harmonics from 1st to 21st are.

If i had time i would try our 2205A but wondered if others had had experiences?
 
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Individual harmonics have different limit values. THD isn't enough.

As for the general question, FFT is supported by most modern digital scopes. If you leave some margin to limit values, the measurement should be meaningful for pre-compliance.
 
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Many scopes have FFT, Siglent's low end scopes have one of the better FFT modes (millions of points). Note that scopes typically have ~1% harmonic distortion specs but that's probably ok for your mains work.

Also if you can get samples from a digital scope you already have its not rocket science to run your own FFT on them.
 

This scope...
https://uk.farnell.com/multicomp-pro/mp720009-eu-uk/dso-2-ch-20mhz-10kpts-100msps/dp/3107568

https://www.farnell.com/datasheets/...MI1uL6mfWd5AIV0ud3Ch11rw2CEAAYASAAEgKXj_D_BwE

...purports to be able to do FFT...so we can use this?
The datasheet of the scope doesnt give too much away.

I reckon we’d need to collect at least three mains cycles of mains input current…….so with 10000 samples of the memory depth, that’s a sample every 6us…easily enough to get up to the 21st mains harmonic. Would you agree?
 

it all depends on how much averaging of each harmonic the meter has to do - if the system under test has a steady state then yes a picoscope FFT will do - if the load is pulsating or time variant then a better meter with averaging is required ...
 

Thanks, its a periodic waveform of period 20ms....every period is identical to the others
 

Hi

Please confirm that you talk about current harmonics (and not voltage harmonics).
(The difference is, that with "current" you simply can focus on your DUT, while with voltage you need to do two measurements with and without your load (to see how much is caused by your DUT) and you need to take mains impedance into account)

You surely can do with a digital system like picoscope ... but the results will deoend a lot on:
* used signal voltage range
* sample rate
* anti aliasing filter
* windowing function (before performing the FFT, because you can't be sure that the sampling frequenc is an integer multiple of mains frequency)
* window size
* mains frequency stability
* mains waveform stability

I agree with FvM, that a refernce measurement with known overtones (but all others signal values should be about identical to your real test signal) is useful to determine accuracy and precision of your test setup.

Klaus
 
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