Patent ID: 6489771
Filing Date: 2002-12-03
Classification: G01V

Abstract:
For detecting the passage along a centerline of a magnetic steel pipeline of a pig containing a permanent magnet, a noise-canceling inductive array for sensing dynamic magnetic flux resulting from passage of the permanent magnet comprising:first and second substantially identical magnetic steel cores in end-to-end spaced-apart alignment on a common longitudinal axis; first and second substantially identical inductive coils uniformly wound about said first and second cores, respectively, said coils being symmetrically displaced from an array axis perpendicular to said longitudinal axis and bisecting a space between said cores; means electrically connecting said coils in series and out of phase; means for securing said cores and coils externally of the pipe with said longitudinal core axis parallel to the pipe centerline; means electrically connected to said coils for detecting at least non-symmetrical portions of a Faraday induced electromotive force across said coils; and means responsive to said detecting means to indicate the passage of the permanent magnet across said array axis.