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Interesting Current Probe

Discussion in 'Electronic Design' started by JB, Oct 6, 2011.

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  1. JB

    JB Guest

    I received this mailshot this morning:
    On the face of it, this could be a very useful probe indeed. There have been
    several occaisions where I have needed to measure actual AC current in a
    Anyone seen/used one of these or have any opinions?
    Thanks in advance.
  2. JB

    JB Guest

    Yes I saw that, but still a lot cheaper than my Tek P6021 (overkill
    admittedly as most of my applications are in the 1kHz-1.5MHz range) and of
    course the Iprober does DC too. I will see if I can get a demo.

  3. Nico Coesel

    Nico Coesel Guest

    Well, that disclaimer goes for about any measurement you make :) I
    recently had a problem with a switcher design so I really needed to
    measure the currents. Preferably primary and secondary. I used 2 SMD
    current sensing transformers to make 2 current probes. Works like a
  4. Yes I got this too and am thinking of getting one.

    It looks like the "sniffer probe" idea described in Appendix E of this
    Jim Williams app note (AN118):

    < Note/an118fa.pdf>

    There look to be enough details to make your own or you could buy

    This new one claims a new type of sensor IIRC, could be a useful
    addition to the collection. But it not clear if it has any advantages
    over a home made one.

    Not as accurate as a proper current probe and more expensive than some
    second hand ones. But the whole point is that you can probe around PCB
    tracks without having to break the circuit.
  5. Joerg

    Joerg Guest

    That one is not going all the way down to DC. Which is rarely needed
    anyhow. But I found that probes being sideways at the end are better,
    they couple much more tigghtly to the trace. So that's what I am using
    in my noise hunts. I have an EMCO near field kit.

  6. Yes good point, forgot about that. Hall sensor?
  7. Several years ago I asked here if scrap hard drive heads could be used
    to make a current probe (of some limited bandwidth). If you only need
    AC measurement I still wonder if a poor man's version is feasible.

    (Cross-posting to csiphs where people have an interest in HDD heads.)
  8. Arno

    Arno Guest

    I doubt it. The problem is that any reasonable current probe
    needs to wrap a core around the wire being probed and then
    reads the current on a second winding. That is the reason
    for the "clamp" design. The "clamp" is actually a ferrite
    core. If you do not do it that way, you get extreme influence
    from distance, 1/(d^2) for a straight wire.

    Also, HDD heads are both extremely fragile and used for
    high field strengts at high frequencies. I do not see them
    ever working reasonably as current probe, even if you
    glue them to the wiore being probed. The amount of advanced
    DSP needed to make sense from their output is just not worth

  9. The probe in discussion (link quoted above) has all the same drawbacks
    (except bandwidth limitation) but costs $800. I thought a head might
    provide the assembly for a poor man's version.

    A head is essentially like the probe in Appendix E here: Note/an118fa.pdf

    But I guess a head might be designed for a very narrow band.
  10. Also, it might be used for finding sources of EMI rather than precise
    current measurement.
  11. Rich Grise

    Rich Grise Guest

    Why not use The Scientific Method - try it! See what happens, then report
    back with your results. My first thought was "no way!", but if you can
    figure out how to "aim" it, you might be able to probe current in PC board

    But someone has to try it to find out if it's worth the bother. :)

    Good Luck!
  12. Fred Abse

    Fred Abse Guest

    I'd be interested to see how it copes with multilayer PCBs.

    A lot of the time, the current I'm interested in is in an inner layer.
  13. Sjouke Burry

    Sjouke Burry Guest

    I would advise to use read/write heads from an old floppy,
    they have a handy size, and wont break so easely.
    Also you dont need a magnifier glass to see them......
  14. Arno

    Arno Guest

    Why don't you just build one as in Figure E1? Does not look
    difficult. I doubt a HDD head is suitable for this at all.

  15. I asked first if it was theoretically feasible, so it doesn't make sense
    to tell me that it isn't but I should try it anyway, but next time I
    have a scrap drive I'll give it a shot.
  16. JB

    JB Guest

    Very good point indeed! I will ask the suppliers.

  17. Arno

    Arno Guest

    Aehm, Figure E1 does not use a HDD head, i.e. I did not tell
    you to try anyways? Still, trying does nor hurt. But the
    comment that modern heads are magneto-resistive and hence
    do not use coils would at least require an adapted amplifier.

  18. josephkk

    josephkk Guest

    I just scrapped a drive last month. Would you like the head stack?

  19. Oh sorry. I Misread. Anyway it's interesting even when you learn you
    can't do something and why.
  20. Franc Zabkar

    Franc Zabkar Guest

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