Patent ID: 7239132

Claim:
An apparatus for detecting a tubular object passing through a longitudinal bore of a tubular member the apparatus comprising: a plurality of magnetic units housed in the tubular member perpendicular to the direction of movement of the tubular object passing through the tubular member; the magnetic units including at least one magnetic field-generating unit having a magnetic axes oriented toward a central point in the longitudinal bore and configured to generate magnetic flux lines perpendicular to the longitudinal bore that form magnetic field, and a plurality of magnetic field-measuring magnetic units configured to generate an induced voltage as a function of the magnetic flux permeating across the longitudinal bore to the magnetic field-measuring magnetic units, wherein the magnetic flux permeating across the longitudinal bore and the magnetic field are modified by the tubular object passing through the longitudinal bore; the magnetic field-measuring magnetic units configured to generate sensing signals representing the induced voltage; and an evaluation device configured to receive and analyze the signals as the tubular object passes through and modifies the magnetic field.