Fast testing of permanent magnets for magnetic position sensors[EPFL]

mt7344

Abstract. Most vendors of permanent magnets quote the tolerances in the remanent flux density +/-5% and the magnetization orientation tolerances +/-5°. For some applications of permanent magnets, notably for those in magnetic position sensors and in free electron radiation sources, these tolerances are too large. In this paper we present an apparatus dedicated for fast testing and sorting of permanent magnets. The apparatus consists of four 3-axis Hall probes, analogue electronics, A/D converter, computer, and LabVIEW-based software. The Hall probes are arranged around the magnet under test so as to allow both an easy positioning of the magnet and easy determination of its characteristics. In the global mode of operation, the system determines the magnetic moment of a magnet (its magnitude, position coordinates, and inclination angles), and its remanent flux density. In the local mode of operation, the system determines the magnitude, orientation, and gradient of the magnetic field in a small volume of interest. The measurements can be done “on the fly”, i.e. by moving the magnet very fast via the testing position.
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