Arrangement with field correcting structure producing a homogeneous magnetic field at a sensor zone for detecting movement of a ferromagnetic element

An arrangement for detecting a ferromagnetic element moving past said arrangement, comprising

• (a) a magnet including a pole face having a mounting zone in a portion of said pole face, said mounting zone being disposed parallel to a direction of movement of a ferromagnetic element moving past said mounting zone,
• (b) field correction means for producing a substantially homogeneous magnetic field at said mounting zone with magnetic lines of force at said mounting zone being substantially at right angles to said pole face, said field correction means comprising a groove in said pole face at said mounting zone, said groove extending through a central part of said pole face substantially orthogonal to said direction of movement of said ferromagnetic element, and
• (c) a sensor mounted in said mounting zone of said magnet so that said magnetic lines of force are substantially at right angles to both said pole face and said mounting zone, said lines of force also penetrating said sensor at substantially right angles,
• wherein said groove has a width exceeding a dimension of said sensor in a direction parallel to said direction of movement.