Pipe current detector with plural magnetic flux detectors

Claim 1

Apparatus for detecting and determining the amplitude and direction of any electric current that may be flowing axially in a buried pipeline in the earth, at a selected point along said pipeline, comprising: (a) first and second magnetic flux detectors spaced apart horizontally a selected distance; (b) said detectors mounted with axes vertical, on a non-magnetic frame, the plane of which is substantially perpendicular to the direction of the pipeline, at a selected distance above the pipeline; (c) means to position said frame and flux detectors along said pipeline at said selected point with said detectors positioned symmetrically, one on each side of the vertical plane through the pipeline, whereby the vertical component of the earth's magnetic field will be equal, and the same direction, while the magnetic flux due to an axial current in said pipeline will be in opposite directions in each of said two detectors; (d) means for making a single point measurement by differentially connecting said first and second flux detectors so as to determine the flux through said detectors due to an axial current in said pipeline at said selected point; and including; (e) vertical third magnetic flux detector means, positioned with its axis midway between said first and second magnetic flux detectors; (f) fourth magnetic flux detector positioned at a known selected distance horizontally from said third magnetic flux detector, said fourth magnetic flux detector pivoted for rotation about a horizontal axis in said vertical plane perpendicular to said pipeline; (g) means to rotate said fourth magnetic flux detector means until a minimum flux passes through it; and (h) means for determining the angle between the horizontal and the axis of said fourth detector; whereby the vertical distance between said first and second magnetic flux detectors and the axis of said pipeline can be determined.