COMPENSATING MAGNETIC INTERFERENCE FOR ELECTRONIC MAGNETOMETER SENSORS

• US 20150000145A1
• Filed: 06/18/2014
• Published: 01/01/2015
• Est. Priority Date: 06/20/2013
• Status: Active Grant

• Current Assignee: Stmicroelectronics Investment Company Limited (STMicroelectronics NV)
• Original Assignee: Stmicroelectronics Investment Company Limited (STMicroelectronics NV)
• Inventors: Tu, Travis, Fang, Shu
• Granted Patent: US 9,506,755 B2
• Time in Patent Office: Days
• US Class Current: 33/303
• CPC Class Codes: G01C 17/28 Electromagnetic compasses with north seeking magnetic elements and having electric pick-offs G01C17/26
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01R 33/007 Environmental aspects, e.g. temperature variations, radiation, stray fields G01R33/025 takes precedence
• CPC Class Codes: G01R 33/0082 Compensation, e.g. compensating for temperature changes

Abstract

Apparatus and methods to compensate hard iron and soft iron magnetic interference in magnetic sensing devices are described. Hard and soft iron interference may be modeled using an ellipsoidal surface generated by a plurality of magnetic field measurements. A displacement of the ellipsoid from a reference frame origin corresponds to hard iron or permanent magnetic field interference. A shape and orientation of the ellipsoid corresponds to soft iron magnetic field interference. The ellipsoidal surface may be analyzed to obtain magnetic field compensation values for cancelling hard iron and soft iron interference.

Claims

1. An electronic device configured to sense a magnetic field comprising:

a magnetometer configured to measure at least one value of an external magnetic field along at least one axis; and

at least one processor configured to receive magnetic field data from the magnetometer and to calculate at least one parameter of an ellipsoid, wherein the magnetic field data is representative of the ellipsoid.

2. The device of claim 1, further comprising a visual display wherein the at least one processor is further configured to compensate, based on the calculated at least one parameter, at least one measured value of the external magnetic field and to cause display of a navigational aid on the visual display to a user of the device.

3. The device of claim 2, wherein the navigational aid is representative of a compass heading.

4. The device of claim 1, wherein the at least one processor comprises a field programmable gate array.

5. The device of claim 1, wherein the at least one parameter includes a location of the center of the ellipsoid with respect to an origin of a spatial frame of reference.

6. The device of claim 5, wherein the spatial reference frame is aligned to the device.

7. The device of claim 5, wherein the at least one processor is further configured to determine an offset calibration parameter to compensate for a displacement of the location of the center of the ellipsoid from the origin of the spatial frame of reference.

8. The device of claim 7, wherein the at least one processor is further configured to apply the offset calibration parameter to measured magnetic field data received from the magnetometer.

9. The device of claim 1, wherein the at least one parameter includes radii of the ellipsoid.

10. The device of claim 9, wherein the at least one processor is further configured to determine recovery calibration parameters to compensate for differences of the radii of the ellipsoid from a spherical surface.

11. The device of claim 10, wherein the at least one processor is further configured to apply the recovery calibration parameters to measured magnetic field data received from the magnetometer.

12. The device of claim 10, wherein the at least one parameter further includes spatial orientations of the radii.

13. The device of claim 10, wherein the at least one processor is configured to determine recovery calibration parameters by calculating eigenvalues of a matrix of coefficients, wherein the coefficients relate to an equation that is descriptive of the ellipsoid.

14. A method for compensating a sensed magnetic field wherein the magnetic field is sensed by a device having at least one processor and a magnetic sensor, the method comprising:

measuring, with a magnetic sensor, at least one value of an external magnetic field along at least one axis;

receiving, by the at least one processor, magnetic field data from the magnetometer; and

calculating, by the at least one processor, a center and at least one additional parameter of an ellipsoid, wherein the magnetic field data is representative of the ellipsoid.

15. The method of claim 14, further comprising:

compensating, by the at least one processor and based on the calculated center and at least one additional parameter, at least one measured value of the external magnetic field; and

displaying, on a visual display of the device, a navigational aid to a user of the device.

16. The method of claim 15, wherein the navigational aid is representative of a compass heading.

17. The method of claim 14, wherein the at least one processor comprises a field programmable gate array.

18. The method of claim 14, wherein a location of the center of the ellipsoid is calculated with respect to an origin of a spatial frame of reference that is aligned to the device.

19. The method of claim 18, further comprising determining, by the at least one processor, an offset calibration parameter to compensate for a displacement of the location of the center of the ellipsoid from the origin of the spatial frame of reference.

20. The method of claim 19, further comprising applying, by the at least one processor, the offset calibration parameter to measured magnetic field data received from the magnetometer.

21. The method of claim 14, wherein the at least one additional parameter includes radii of the ellipsoid.

22. The method of claim 21, further comprising determining, by the at least one processor, recovery calibration parameters to compensate for differences of the radii of the ellipsoid from a spherical surface.

23. The method of claim 22, further comprising applying, by the at least one processor, the recovery calibration parameters to measured magnetic field data received from the magnetometer.

24. The method of claim 22, wherein the at least one additional parameter further includes spatial orientations of the radii.

25. The method of claim 22, wherein the determining recovery calibration parameters comprises calculating, by the at least one processor, eigenvalues of a matrix of coefficients, wherein the coefficients relate to an equation that is descriptive of the ellipsoid.