+ Post New Thread
Results 1 to 12 of 12
  1. #1
    Advanced Member level 5
    Points: 32,926, Level: 44
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    6,851
    Helped
    496 / 496
    Points
    32,926
    Level
    44

    Cheap Mains harmonics tester

    Hello,
    Do you know of cheap equipment that can be used to measure Mains harmonics in our <200W offline LED drivers?
    We wonder how accurate the FFT function of picoscope 2205A is at this.

    Picoscope 2205A
    https://www.picotech.com/download/da...a-sheet-en.pdf

    •   AltAdvertisement

        
       

  2. #2
    Super Moderator
    Points: 260,203, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,441
    Helped
    13825 / 13825
    Points
    260,203
    Level
    100

    Re: Cheap Mains harmonics tester

    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.


    1 members found this post helpful.

  3. #3
    Advanced Member level 5
    Points: 32,926, Level: 44
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    6,851
    Helped
    496 / 496
    Points
    32,926
    Level
    44

    Cheap Mains harmonics tester

    Hi
    This is a continuation of this thread if i may which is closed...

    https://www.edaboard.com/showthread....rmonics-tester

    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?
    Last edited by FvM; 17th September 2019 at 12:10. Reason: Merged with previous thread



  4. #4
    Advanced Member level 5
    Points: 14,943, Level: 29
    schmitt trigger's Avatar
    Join Date
    Apr 2013
    Posts
    2,483
    Helped
    805 / 805
    Points
    14,943
    Level
    29

    Re: Cheap Mains harmonics tester

    Do you require individual harmonic level, or would a THD measurement be sufficient?
    My batteries are recharged by "Helpful Post" ratings.
    If you feel that I've helped you, please indicate it as a Helpful Post


    1 members found this post helpful.

  5. #5
    Super Moderator
    Points: 260,203, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,441
    Helped
    13825 / 13825
    Points
    260,203
    Level
    100

    Re: Cheap Mains harmonics tester

    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.


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  6. #6
    Advanced Member level 3
    Points: 5,825, Level: 18

    Join Date
    Feb 2014
    Posts
    828
    Helped
    273 / 273
    Points
    5,825
    Level
    18

    Re: Cheap Mains harmonics tester

    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.



  7. #7
    Advanced Member level 5
    Points: 32,926, Level: 44
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    6,851
    Helped
    496 / 496
    Points
    32,926
    Level
    44

    Re: Cheap Mains harmonics tester

    This scope...
    https://uk.farnell.com/multicomp-pro...sps/dp/3107568

    http://www.farnell.com/datasheets/28...SAAEgKXj_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?



  8. #8
    Advanced Member level 3
    Points: 5,825, Level: 18

    Join Date
    Feb 2014
    Posts
    828
    Helped
    273 / 273
    Points
    5,825
    Level
    18

    Re: Cheap Mains harmonics tester

    Treez for cheap scopes Siglent is the best at the moment with the FFT feature being one of the selling points. It's better than our $50k tektronix.
    https://www.tester.co.uk/sds1000x-e-4ch

    https://www.siglenteu.com/digital-os...oscilloscopes/



  9. #9
    Advanced Member level 5
    Points: 11,060, Level: 25

    Join Date
    Aug 2015
    Posts
    1,803
    Helped
    667 / 667
    Points
    11,060
    Level
    25

    Re: Cheap Mains harmonics tester

    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 ...



    •   AltAdvertisement

        
       

  10. #10
    Advanced Member level 5
    Points: 32,926, Level: 44
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    6,851
    Helped
    496 / 496
    Points
    32,926
    Level
    44

    Re: Cheap Mains harmonics tester

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



  11. #11
    Super Moderator
    Points: 77,731, Level: 67
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    15,754
    Helped
    3589 / 3589
    Points
    77,731
    Level
    67

    Re: Cheap Mains harmonics tester

    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
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


    1 members found this post helpful.

  12. #12
    Advanced Member level 5
    Points: 32,926, Level: 44
    Achievements:
    7 years registered

    Join Date
    Sep 2008
    Location
    cambridge
    Posts
    6,851
    Helped
    496 / 496
    Points
    32,926
    Level
    44

    Re: Cheap Mains harmonics tester

    Thanks, yes we are interested in current harmonics.



--[[ ]]--