Calibrating a magnetic sensor in a mobile device using a field model

摘要

A magnetic sensor, e.g. a magnetic compass in a mobile telephone handset, is calibrated by fitting measured data to an ellipsoid and comparing with reference magnetic field data e.g. from a model. The location of the sensor is determined e.g. from a GPS signal and the values of the Earth's field at that location are obtained from a reference field model e.g. the International Geomagnetic Reference Field. The calibration process can use the normal motion of the handset to obtain measurement data from the three orthogonal axes of sensor rather than a separate calibration motion. The calibration process can be repeated automatically if the position of the device is too far from the point of last calibration. Hard iron effect, soft iron effect and scale factors can be corrected by comparison to a sphere represented by magnetic field data from the model at the sensor's location.