Method and apparatus for calibrating a magnetic sensor

• US 8,825,426 B2
• Filed: 04/09/2010
• Issued: 09/02/2014
• Est. Priority Date: 04/09/2010
• Status: Active Grant

• Current Assignee: CSR Technology Holdings Inc. (Qualcomm, Inc.)
• Original Assignee: CSR Technology Holdings Inc. (Qualcomm, Inc.)
• Inventors: Chowdhary, Mahesh, Jain, Mahaveer
• Primary Examiner(s): SUGLO, JANET L
• Application Number:
  US12/757,908
• Publication Number:
  US 20110248704A1
• Time in Patent Office: 1,607 Days
• Field of Search: 702/85, 702/94, 702/95, 702/104, 702/150
• US Class Current: 702/95
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01D 18/004 Continuous recalibration
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration

Abstract

In general, the invention relates to an algorithm and process for automated and/or continuous calibration of magnetic sensor, for example such as a sensor installed in a mobile positioning system handset. According to certain aspects, the calibration process can use the normal motion of the handset such that all measurement data from the three orthogonal axes of sensor when exposed to Earth'"'"'s magnetic field is collected. According to still further aspects, the process includes fitting measurement data to an ellipsoid that characterizes the actual magnetic field measurements from a magnetic sensor, so that anomalies such as hard iron effect, soft iron effect and scale factors can be extracted and/or corrected by comparison to a sphere represented by magnetic field data from a model at the sensor'"'"'s location.

Claims

1. A method for calibrating a magnetic sensor implemented by one or more integrated circuits, the method comprising:

obtaining location-based magnetic field values for a location;

obtaining magnetic field measurements from the magnetic sensor corresponding to the location;

fitting the obtained magnetic field measurements to an ellipsoid using the one or more integrated circuits;

extracting calibration values using the ellipsoid and obtained location-based magnetic field values;

detecting motion of a device including the sensor, wherein the magnetic field measurements obtaining step is performed in conjunction with the detected motion; and

monitoring the detected motion to detect acceleration spikes above a predetermined threshold, wherein the obtained magnetic field measurements during the detected acceleration spikes are discarded.

2. A method according to claim 1, wherein the magnetic field measurements obtaining step includes obtaining magnetic field measurements for three orthogonal axes.

3. A method according to claim 2, further comprising detecting motion in the three orthogonal axes of a device including the sensor, wherein the magnetic field measurements obtaining step is performed in conjunction with the detected motion.

4. A method according to claim 1, wherein the magnetic field measurements obtaining step includes automatically obtaining the measurements during normal operation of a device including the sensor.

5. A method according to claim 4, wherein the device includes a telephone, and wherein the normal operation includes using the telephone during a telephone call.

6. A method according to claim 1, further comprising obtaining the location from a location positioning system.

7. A method according to claim 6, wherein the location positioning system comprises GPS.

8. A method according to claim 6, wherein the location positioning system comprises WiFi.

9. A method according to claim 1, wherein the location-based magnetic field values obtaining step includes obtaining the values from a model using the location as an input to the model and receiving the location-based magnetic field values as an output from the model.

10. A method according to claim 9, wherein the model comprises the International Geomagnetic Reference Field model.

11. A method according to claim 1, wherein the fitting step includes:

expressing the location-based magnetic field values in terms of raw measurements;

arranging terms in the expression to correspond to ellipsoid coefficients; and

using a least squares method to determine values for the ellipsoid coefficients.

12. An apparatus for performing the method of claim 1.

13. A method for calibrating a magnetic sensor implemented by one or more integrated circuits, the method comprising:

obtaining location-based magnetic field values for a location;

obtaining magnetic field measurements from the magnetic sensor corresponding to the location,

fitting the obtained magnetic field measurements to an ellipsoid using the one or more integrated circuits; and

extracting calibration values using the ellipsoid and obtained location-based magnetic field values,

wherein the fitting step includes expressing the location-based magnetic field values in terms of raw measurements as a function of magnetic field error components, and

wherein the expression comprises;

14. A method according to claim 13, wherein the error components include components of one or more of hard iron effect, scale factor and soft iron effect.

15. A method according to claim 14, further comprising detecting motion in three orthogonal axes of a device including the sensor, wherein the magnetic field measurements obtaining step is performed in conjunction with the detected motion.