Patent ID: 7449879
Filing Date: 2008-11-11
Classification: E21B,G01V

Abstract:
1. An apparatus for detecting an object passing through a bore in a member, the bore forming an interior wall of the member, the apparatus comprising: an evaluation device having a power source and a signal processor; a plurality of magnetic units circumferentially disposed around the interior wall of the member, each magnetic unit being individually connected to the evaluation device; at least one of the plurality of magnetic units being connected to the power source and generating a magnetic field within the bore of the member; at least two or more of the plurality of magnetic units being connected to the signal processor, each magnetic unit connected to the signal processor measuring a magnetic flux of the magnetic field; the magnetic flux of the magnetic field being modified by the passage of the object through the bore of the member, the magnetic units connected to the signal processor generating signals representing the modifications to the magnetic flux; and the evaluation device receiving the signals and detecting the modifications to the magnetic field caused by the object moving through the magnetic field.