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dirty waveform

Discussion in 'General Electronics Discussion' started by docb, Dec 22, 2015.

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  1. docb

    docb

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    Feb 11, 2010
    I'm looking at the output of a wall powered driver on a scope. The bottom of the square wave, (meaning 0v), is messy, presumably because the output ground isn't tied to the input ground, so it's floating.

    I want to use this output to control a device I will make, but not sure what to do to eliminate this noise.
     
  2. Gryd3

    Gryd3

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    Jun 25, 2014
    what waveform... and how is it 'messy' ?
    This could be drift, ringing, or simply an undesirable shape...
    More info is most certainly needed here.
     
  3. davenn

    davenn Moderator

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    and what is a wall powered driver ?
     
    Arouse1973 likes this.
  4. docb

    docb

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    Feb 11, 2010
    It's a light driver, powered from AC line voltage.
     
  5. Gryd3

    Gryd3

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    Again... can you please provide more details.

    What is the waveform ?
    How is it dirty ?
    Do you have a picture?
     
  6. docb

    docb

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    Feb 11, 2010
    upload_2015-12-22_15-17-6.jpeg
     
  7. Gryd3

    Gryd3

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    Jun 25, 2014
    Now isn't that odd...
    I'm not sure what to make of that... It looks like 3 or 4 different shapes superimposed on each other. I would not associate that with a lack of ground between input and output.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Do a 1-shot capture. What you're seeing is varying waveforms being superimposed.
     
  9. dorke

    dorke

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    Jun 20, 2015
    And please show a photo of all the Scope knobs and settings
     
  10. davenn

    davenn Moderator

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    in some ways, it looks like ringing
     
  11. docb

    docb

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    Feb 11, 2010
    What do you want to see on the knobs? I think the screen shows all the settings.
     
    (*steve*) likes this.
  12. dorke

    dorke

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    Jun 20, 2015
    I'm not familiar with that specific scope and the way "settings" are displayed on the CRT.

    What are(though a picture is worth thousand words ;)):

    1.The trigger setting.
    2.Acquisition method.
    3.Time/div
     
  13. docb

    docb

    131
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    Feb 11, 2010
    upload_2015-12-23_8-56-47.jpeg


    This picture show time div.
    Acquisition method is "sample", so maybe that's the issue. If I use "average "it looks much better:

    upload_2015-12-23_9-1-48.jpeg
     
  14. dorke

    dorke

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    Jun 20, 2015
    What kind of signal is it?
    Is the trigger level about 19V?

    No, averaging is a distortion of reality.
    Can you use a "single time Acquisition"

    What is the ground clip of the scope probe connected to?
     
  15. docb

    docb

    131
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    Feb 11, 2010
    The second image is a single. Ground clip is on negative output of the driver. Other is on positive. Yes, trigger anywhere above about 13 seems ok.
     
  16. dorke

    dorke

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    Jun 20, 2015
    Take a single sample,without average.and show it
    After the data is in the scope memory ,zoom in the area shown and show it as well.

    upload_2015-12-23_9-1-48.jpeg
     
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    No need to see that in more detail. It's clearly ringing on the negative edge.

    Now, what is this actual device, and what sort of load is it powering when you take these readings?
     
  18. dorke

    dorke

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    Jun 20, 2015
    Steve,it isn't classical ringing as the final low voltage is at or below the minimum of the "ring" .

    Also look at this from post 13.
    Not clear at all. upload_2015-12-23_8-56-47.jpeg
     
    Gryd3 likes this.
  19. GPG

    GPG

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    Sep 18, 2015
    Could be 1/2 bridge with faulty low side drive.
     
  20. dorke

    dorke

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    Jun 20, 2015
    Yes,could be.
     
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