Appeal No. 1997-2245 Page 12
Application No. 08/402,872
(id.) it would have been obvious to have used flux-gate
sensors. We note that claim 2 requires a flux-gate compass,
and not just a flux-gate sensor. The examiner states
(answer, page 4) that "Applicant is correct in stating that
Golden et al., similar to Mishin, Weitschies et al., and Macri
et al., senses magnetic field strength." We find that in
Golden (col. 5, lines 37-43) the location of a medical tube is
detected by sensing the static magnetic field strength
gradient produced by a permanent magnet associated with the
tube. A magnet 91 (figure 4) is associated with a medical
tube, such as a motility catheter (col. 5, lines 29 and 30).
Sensing of the magnetic field strength is performed by a
detection apparatus including a pair of flux-gate sensors 81a
and 81b. Each sensor includes a toroid 10a, 20a, excitation
winding 10c, 20c, and detection windings 10b, 20b. The flux-
gate sensors (figure 3 and col. 9, lines 3-16) are spaced
apart and fixed at each end of a mounting arm 82 with their
detection winding axes aligned and parallel to the length of
the mounting arm. The purpose of spacing the sensors is to
separate out the earth's ambient magnetic field from the
magnetic field of the magnet. The earth's magnetic field
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