Magnetic field sensor system with a biasing magnet producing a spatially symmetric magnetic field within a plane being defined by magnetoresistive sensor elements

摘要

It is described a magnetic field sensor system (200, 400, 500) for measuring rotational movements of a shaft. The magnetic field sensor system (200, 400, 500) comprises (a) a biasing magnet (210, 410, 510) configured for generating a biasing magnetic field; (b) a magnetic wheel (230) having a wheel axis and a circumferential surface which comprises a regular structure of teeth (231) and gaps (232) arranged in an alternating manner, wherein (i) the magnetic wheel (230) is attachable to the shaft and (ii) the magnetic wheel (230) can be magnetized by the biasing magnetic field; and (c) a magnetoresistive sensor arrangement (220) comprising four magnetoresistive sensor elements (221, 222, 223, 224; 521, 522, 523, 524) being connected with each other in a Wheatstone bridge, wherein respectively two of the magnetoresistive sensor elements (221, 222, 223, 224; 521, 522, 523, 524) are assigned to one half bridge of the Wheatstone bridge. The four magnetoresistive sensor elements (221, 222, 223, 224; 521, 522, 523, 524) are arranged within an x-y plane, wherein an x-axis, a y-axis and a z-axis define an orthogonal Cartesian coordinate system in which (i) the x-axis is oriented parallel with the wheel axis of the magnetic wheel (230), (ii) the y-axis is oriented tangential to the circumferential surface of the magnetic wheel (230), and (iii) the z-axis is the symmetry line through the center of the biasing magnet (210, 410, 510) and the center of the magnetic wheel (230). The biasing magnet (210, 410, 510) is configured in such a manner that the y-component of the biasing magnetic field is symmetric with respect to the y=0 plane.