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Eddy current project

Discussion in 'Electronic Design' started by Jamie, Nov 27, 2010.

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  1. Jamie

    Jamie Guest

    We have a project at work that has been doing well for some time now,
    and that is an Eddy/(foucault)current method of detecting surface
    defects and cracks in copper conductor.. This includes stranded and
    solid.. I guess it works for Tungsten, AL, and nickel, too!

    There is going to be some changes made in the processing of the material
    and I was asked, if it would be possible to submerge the coils in the
    coolant water. I didn't give them an answer, still thinking about this..

    We can protect the coils from water how ever, we use recycled water
    for cooling and its not drinkable but on the other hand, does come out
    clean looking, due to our filtration system.. Was wondering if any one
    could shed some light on the effects I should be seeing when I place the
    detector coils in the water? We do add a chemical to the water because
    it's too hard from what I understand..

    I guess the problem is, they need more coolant time and need the
    space the detector is using, inline.. So the solution would be to have
    this device in the water where the wire will be passing through.. This
    test can also detect the sudden lose of insulation due do the Eddy
    currents generating a phase shift. So, the thought of water around the
    area tells me that this part of the test maybe ignored?

    We do have a unit that measures wall thickness that uses eddy currents
    how ever, that is not designed to be submerged in water..

    Any comments on this would be appreciated..

  2. Jamie

    Jamie Guest

    I'll need to do some R&D on that idea. The coil I have now is potted, I
    was wondering what the effects would be when water is filling the void
    between the coils and SUT.

    I suppose I could calibrate the system with water required if there
    is an adverse change..


  3. Joerg

    Joerg Guest

    This section of NDT isn't too familiar to me but I have heard of
    "underwater" use in the nuclear energy field. AFAIK to measure the crud
    layer on fuel rods. There is also a pulse eddy current technique used on
    oil rigs and the like, underwater, but IIRC that is limited to steel.

    You might want to take a peek into those fields.
  4. Rich Grise

    Rich Grise Guest

    Pure, clean (i.e., distilled) water is a pretty good insulator - people use
    it all the time for cooling stuff, but if it's got ions in it (which your
    supply sounds like - even "deionized" or "soft" water still has ions, just
    not the kind that precipitate out on your faucets and stuff) it will be

    Before I use your reclaimed water, I'd check its conductivity - you probably
    don't want your coolant shorting out your experiment. =:-O

    Good Luck!
  5. Tim Williams

    Tim Williams Guest

    DI is DI, period. "Soft" means replacing hard ions with soft ions
    (replacing calcium and magnesium with sodium or potassium). In general,
    water softeners add TDS.

    C'mon Rich, this stuff is on *Wikipedia* for petes sake.

  6. Rich Grise

    Rich Grise Guest

    Well, OP didn't say what kinds of voltages are involved, but personally,
    I wouldn't use "reclaimed" water to cool something electric.

  7. Jamie

    Jamie Guest

    The coils are potted, so their won't be an issue with conductivity, Its
    the behavior of the eddy currents through this water that is in question.

    Tomorrow if I get a chance, i'll find a production line I can
    experiment on..

  8. RoV

    RoV Guest

    "Jamie" wrote in message news:RGuIo.47645$...
    These sensors work with highly conductive seawater. Coils are obviously

    Water will certainly attenuate your returned signal and give extra returns.
    For example this is an issue for the above cited instrument in very shallow
    water, when you can have returns from the top when you are actually looking
    towards the bottom.

    -- RoV - IW3IPD
  9. Jamie

    Jamie Guest


    I will be back to work tomorrow and will subject the coils to some
    harsh testing.

    It's hard to do R&D out side of work with out dumping too much
    information that may end up in the competitors lap..

    The idea of this isn't new and the implementation of it has its
    various methods. We have come up with working units that didn't cost
    hardly much at all to design and construct.

    The lowest cost unit we could find that would do what we wanted out
    of water was starting at $12k per unit. We just thought that was a
    little much and stuck with the more archaic devices we were using at
    the time.

    This will probably end up like one of my other little designs that some
    how ended up in the lap of a fab house where they had their own
    engineers. It was funny because we have other plants and share our
    information of course. We received a unit that was being used at one of
    our competitors, to evaluate the performance and if it looked ok, they
    were going to buy some. It was a big surprise when we looked in the back
    of the small paper back manual, A photo copy of my schematic with
    my initials down at the lower right. Not very sharp looking due to the
    poor copy but they were mine, nonetheless.

    You see, the CAD program we were using and still do for some things
    is a custom written program and the file format is not compatible with
    anything out there, so I guess a photo copy was the simplest thing to
    do.. Which means, some one in one of our plants must of distributed the
    manual or a complete device.

    I think what really happen was they had this fab shop assemble them
    and they took up the pose of distributing them. The unit on the outside
    didn't look like ours and had their name on it how ever, the board
    inside was exactly as ours.

    So, since this has happen, I was told not to get to friendly with the
    information of future projects.. Since most of us signed a
    confidentiality agreement..

    I am sure many others here have run into similar situations.

    Oh well, such as life..

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