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vibrating coil gradiometer

Discussion in 'Electronic Design' started by George Herold, Oct 31, 2012.

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  1. Yeah no torroids.... unless you're making a flux gate thing.
    So you're saying there will be very little voltage gain, with a
    ferrite plus coil, vs just the coil? (I must admit I find magnetic
    materials a confusing lot.) That's OK I hopefully won't make the same
    mistake twice.

    George H.
     
  2. Tim Williams

    Tim Williams Guest

    Oh, there's gain, just not mu times -- should be roughly the ratio of
    lengths, core to coil. So a 6" loopstick in an AM radio works a lot
    better than the teeny winding on it, etc.

    Tim
     
  3. Hmm OK thanks, If I want to shake it around it's not worth the extra
    mass... which I guess leads back to James's original idea.

    George H.
     
  4. josephkk

    josephkk Guest

    The cheap answer is like a Pringles.

    http://en.wikipedia.org/wiki/Paraboloid
     
  5. 'scratch scratch'... You're riffin' on James's idea? Isn't this like
    the fluxgate that Jan made (and posted here) a while back? (I've half
    forgotten how that works.)

    George H.
     
  6. Hmm, maybe we are talking about different geometries.
    Googling "toroid fluxgate" I get this,

    www.geotech1.com/pages/mag/projects/fmx1/fmx1.pdf

    The first figure is what I was picturing. I remember going over this
    in my mind when Jan posted it, and I thought I got it.... but I'm
    going to have to draw pictures again.
    (The pickup coil sees a signal at twice the drive frequency, IIRC)
    Say Jan, if you're lurking do you have a good reference for the
    toroidal fluxgate?

    George H.
     
  7. Tim Williams

    Tim Williams Guest

    Hmm, nonuniformity in the toroid is on the order of N turns; you'd need
    over 1000 turns, in a single even layer, to get to that level I'd think.

    Hmm, nah, it wouldn't quite be that bad, nor that easily defined. Each
    turn acts like a dipole at a slightly different angle. After ten turns,
    you have a dodecapole in a circle. A suitable distance from that and your
    far field drops off ridiculously fast (that is, ignoring the solenoidal
    component of a standard progressive winding), isn't it ~1/R^N for an
    N-pole?

    So it comes down to the compromise between relative size (how much space
    you can get between the toroid and solenoid), near field nonuniformity
    (number of turns, and their distribution), and the amount of with-core vs.
    without-core gain you experience from using the toroid as a bar magnet.

    I'm carrying out a thought experiment which seems to suggest there's no
    free lunch here, i.e., it reduces to a linear/folded form of the "no free
    lunch" once-you-saturate-it-the-control-winding-couples-in hypothesis.
    It's just an hypothesis, but there may be a theorem in there.

    Tim
     
  8. Jasen Betts

    Jasen Betts Guest

    This is soething I've just thought up.

    someone said a rotating coil coupled to the leads by a coaxial
    transfromer (like found under VHS drums)

    someone else made a remark (that I may have misread) that started me
    thinking that you could stir the magnetic field and make it pass over
    turns of a stationary coil by combining the two rotating coils into
    a single stirrer


    given that the inner radius of the coils is 1 unit

    For the field baffle with the axle on the Z axis though the origin
    the surface shhould approximate the plane z=y (where xx+yy < 1)

    on further thought most of the current will flow in the edges of the
    baffle, so, a simple inclined elliptical ring would probably work as well
    as he disc does.
    try "z=xy"
     
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