Magnetic leakage field flaw detector utilizing partially overlapping hall probes

Claim 1

Apparatus for detecting elongate flaws in a magnetically energized body having a longitudinal extent, comprising: first and second Hall devices for sensing magnetic flux fringing the surface of said body, each of said devices including a pair of voltage line connection points and being arranged in a manner whereby a straight line extending between said voltage connection points of said first device is generally parallel to a straight line extending between said voltage connection points of said second device and to said longitudinal extent; said Hall devices being arranged with their respective sensing elements having planes which partially overlay and are parallel to each other, each of said planes being defined by the width and length of the respective element and being taken through the thickness of the element, and so that a transverse plane extending through the longitudinal extents of the straight lines, extending between the voltage connection points of each device, deviates from a line normal to the overlaying planes; means for providing a flow of current through the conductor of said first Hall device in a first direction; means for providing a flow of current through the conductor of said second Hall device in a direction opposite to said first direction; means for transmitting a first voltage signal indicative of the fringing magnetic flux sensed by said first Hall device; means for transmitting a second voltage signal indicative of fringing magnetic flux sensed by said second Hall device; and means for summarizing said first and second voltage signals and producing an output indicative of the vector difference of said first and second voltage signals.