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Current clamp difference question...

Discussion in 'Electronic Design' started by Default User, Jun 26, 2008.

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  1. Default User

    Default User Guest

    Hi,

    I measured the current going to my scope using two clamps. One is a
    hall-effect clamp that can do both AC and DC, and the other is just an AC
    only clamp although they both output mV.

    This first waveform shows the AC only clamp and my question is, why are the
    horizontal (no current) areas slanted either upward or downward?

    http://home.earthlink.net/~alank2/clamp2.gif

    This waveform shows both clamps and you can see that the hall effect one
    (light blue) is not distorted and the AC one (yellow) is like the first one:

    http://home.earthlink.net/~alank2/clamp.gif

    Is this sort of distortion normal for an AC only transformer based clamp?

    Thanks,

    Alan
     
  2. Phil Allison

    Phil Allison Guest

    "Default User"

    ** Yep.

    The AC clamp has significant variations in its current sensitivity that
    depend on frequency - ie it has a response that falls away at low and high
    frequencies.

    OTOH, the Hall Effect clamp has response that does not fall away low
    frequencies, but only at some fairly high one.

    Where there are response changes with frequency - there are also phase
    changes with frequency ( all-pass filters notwithstanding).

    So, the slanting ( aka tilt ) you see on the scope trace is the result of
    phase shift ( generated in the AC clamp) between the frequency components of
    that bi-polar pulse waveform.



    ...... Phil
     
  3. Default User

    Default User Guest

    Hi Phil,

    Thanks for explaining it!!! That makes perfect sense!!

    Alan
     
  4. legg

    legg Guest

    Depends on the low frequency bandwidth of the sensor, and the
    frequency of the current waveform. A transformer has a low-frequency
    limit that produces an L/R time constant for waveform droop. Gives the
    same effect as a capacitively-coupled RC time constant.

    Commercial line frequency current transformers can be very droopy,
    particularly clamp-on types with their mechanically-forced gap
    (~reduces L); judging from the additionally poor HF definition, that
    could be what you're dealing with here.

    RL
     
  5. JosephKK

    JosephKK Guest

    Looks like a diode bridge fed into a storage capacitor with a
    switching power supply typical current waveform.
     
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