Precise Alignment of a Magnetic Sensor in a Coordinate Measuring Machine

In order to measure strongly inhomogeneous magnetic fields it is straight forward to mount a magnetic sensor in a coordinate measuring machine (CMM). A scan of the field provides the components of the field vector w.r.t. the coordinates of the CMM reference frame. However, assembly tolerances of the sensor impair the field measurement. This paper explains a calibration procedure how to determine the misalignment of the sensor w.r.t. the reference frame of the CMM. To this end, the sensor needs at least two and for high accuracy four sensor elements on a single die with negligible hysteresis and offset. The calibration procedure requires a reference magnetic field with certain symmetry properties. A magnetic circuit generating this field is shown. Inaccuracies of the sensor elements and a curvature of the die surface are investigated theoretically and exemplary and result in a maximum error smaller than ±0.027°.