Hall-effect ferromagnetic-article-proximity sensor
AssigneeAllegro MicroSystems, LLC
InventorsRavi Vig, Teri L. Tu
Life of this patent
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Abstract
A Hall-effect sensor is presented which is adapted to sense a ferromagnetic object, including an integrated circuit chip having a planar Hall element which is positioned in, parallel to, and defines a sensor plane having a front side and a back side, and which element is normal to and centered on a sensor axis, and a magnet structure having an N pole and an S pole, the magnet structure being positioned behind the sensor plane and positioned so that an S pole and an N pole are adjacent each other and both are adjacent the element.
Claims14
A magnetic-field sensor for detecting the presence of passing ferromagnetic articles comprising:
- a) an integrated circuit chip 12 including a magnetic field sensor element 14 for generating an output voltage that is proportional to the ambient magnetic field;
- and
- b) a magnet structure comprised of a central pole piece 18, a first high magnetic permeability pole piece 16 abutting one side of said magnet 18 and a second high magnetic permeability pole piece 17 abutting the opposite side of said magnet 18, an end of each of at least said first and second pole pieces lying in and defining said front face 15f of said magnet structure 15, said central pole piece being for presenting a magnetic field of one polarity at said front face and said first and second pole pieces being respectively for presenting magnetic fields of the opposite polarity at said front face, said sensor element being centrally mounted to said magnet structure at said front face;
- so that the absolute value of magnetic flux sensed by said magnetic-sensor element is low when there is no passing ferromagnetic article in the vicinity of said sensor element, a high amplitude of flux is sensed by said magnetic-field sensor element at moments when a ferromagnetic article is proximate said magnetic-field sensor element and at moments when the valley between two passing ferromagnetic articles is proximate said magnetic-field sensor element a low value magnetic flux is sensed that is almost independent of the air gap dimension between said sensor element and the passing articles.
A magnetic-field sensor for detecting the presence of passing ferromagnetic articles comprising:
- a) an integrated circuit chip 12 including a magnetic field sensor element 14 for generating an output voltage that is proportional to the ambient magnetic field;
- and
- b) a magnet structure 15 comprising:
- 1) a central magnetic pole piece (18) and two peripheral magnetic pole pieces (16 and 17) respectively abutting two opposite sides of said central magnetic pole piece, a pole end of each of said two peripheral pole pieces coincident with a front face 15f of said magnet structure (15), one pole end of said central magnetic pole piece lying between said peripheral pole-piece ends near said front face, said integrated circuit chip 12 being mounted centrally to said magnet-structure front face;
- and
- 2) a magnet means for generating a magnetic field of one polarity at said one pole end of said central magnetic pole piece, and for generating magnetic fields of the other polarity at said pole ends of said two peripheral magnetic pole pieces;
- so that the absolute value of magnetic flux sensed by said magnetic-sensor element is low when there is no passing ferromagnetic article in the vicinity of said sensor element, a high amplitude of flux is sensed by said magnetic-field sensor element at moments when a ferromagnetic article is proximate said magnetic-field sensor element, and at moments when the valley between two passing ferromagnetic articles is proximate said magnetic-field sensor element a low value magnetic flux is sensed that is almost independent of the air gap dimension between said sensor element and the passing articles.
Dependencies are inferred from the claim text.