METHOD AND APPARATUS FOR CALIBRATING A MAGNETIC SENSOR

• US 20140336968A1
• Filed: 05/07/2014
• Published: 11/13/2014
• Est. Priority Date: 05/08/2013
• Status: Abandoned Application

• Current Assignee: Stmicroelectronics Investment Company Limited (STMicroelectronics NV)
• Original Assignee: Stmicroelectronics Investment Company Limited (STMicroelectronics NV)
• Inventors: Tu, Travis, Fang, Shu
• Application Number:
  US14/271,982
• Publication Number:
  US 20140336968A1
• Time in Patent Office: Days
• US Class Current: 702/87
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration

Abstract

A magnetic sensor is calibrated by acquiring magnetic field measurements, fitting at least part of the plurality of magnetic field measurements to an ellipsoid model to obtain a coordinate of a center of the ellipsoid model, and determining a calibration offset according to the coordinate of the center of the ellipsoid model. The calibration offset is used to calibrate the magnetic sensor. The magnetic sensor itself obtains the magnetic field measurements. A processing device coupled to the magnetic sensor operates to process the magnetic field measurements is accordance with the ellipsoid mode and determine the calibration offset.

Claims

1. A method for calibrating a magnetic sensor, comprising:

acquiring a plurality of magnetic field measurements from said magnetic sensor;

fitting at least part of the plurality of magnetic field measurements to an ellipsoid model to obtain a coordinate of a center of the ellipsoid model;

determining a calibration offset according to the coordinate of the center of the ellipsoid model; and

calibrating the magnetic sensor using the calibration offset.

2. The method of claim 1, wherein said step of fitting comprises:

determining an expression of the ellipsoid model containing a plurality of ellipsoid parameters;

substituting at least part of the plurality of magnetic field measurements into the expression of the ellipsoid model to obtain an equation expressed in way of a matrix of the magnetic field measurements and a matrix of the plurality of ellipsoid parameters;

solving the equation using Gaussian principle elimination to obtain the plurality of ellipsoid parameters; and

determining the coordinate of the center of the ellipsoid model using the plurality of ellipsoid parameters.

3. The method of claim 2, wherein said step of solving comprises:

traversing the matrix of the magnetic field measurements to determine principles thereof;

converting the matrix of the magnetic field measurements into a triangular matrix based on the principles obtained; and

solving the equation based on the triangular matrix to obtain the ellipsoid parameters.

4. The method of claim 2, wherein the expression of the ellipsoid model is defined by:

a₁x²+a₂y²+a₃z²+a₄xy+a₅xz+a₆yz+a₇x+a₈y+a₉z=1

wherein (x, y, z) represents a point located on the ellipsoid model, and a_l-a₉ represent the ellipsoid parameters, and the coordinate of the center of the ellipsoid model is defined by (x₀, y₀, z₀), wherein x₀, y₀ and z₀ are expressed as follows;

5. The method of claim 1, wherein the plurality of magnetic field measurements comprise at least nine different magnetic field measurements.

6. The method of claim 1, wherein each of the plurality of magnetic field measurements is measured along three orthogonal axes.

7. The method of claim 6, wherein the calibration offset is equal to a vector from an origin of the three orthogonal axes to the center of the ellipsoid model.

8. The method of claim 1, wherein said step of calibrating comprises subtracting the calibration offset from the magnetic field measurements.

9. A magnetic sensor, comprising:

an acquiring device configured to acquire a plurality of magnetic field measurements;

a control device configured to fit at least part of the plurality of magnetic field measurements to an ellipsoid model to obtain a coordinate of a center of the ellipsoid model, and to determine a calibration offset according to the coordinate of the center of the ellipsoid model; and

a calibration device, configured to calibrate the magnetic sensor using the calibration offset.

10. The magnetic sensor of claim 9, wherein said control device is configured to fit at least part of the plurality of magnetic field measurements to an ellipsoid model to obtain a coordinate of a center of the ellipsoid model, and comprises elements configured to:

determine an expression of the ellipsoid model containing a plurality of ellipsoid parameters;

substitute at least part of the plurality of magnetic field measurements into the expression of the ellipsoid model to obtain an equation expressed in way of a matrix of the magnetic field measurements and a matrix of the plurality of ellipsoid parameters;

solve the equation using Gaussian principle elimination to obtain the plurality of ellipsoid parameters; and

determine the coordinate of the center of the ellipsoid model using the plurality of ellipsoid parameters.

11. The magnetic sensor of claim 10, wherein the element in said control device configured to solve the equation comprises sub-elements configured to:

traverse the matrix of the magnetic field measurements to determine principles thereof;

convert the matrix of the magnetic field measurements into a triangular matrix based on the principles obtained; and

solve the equation based on the triangular matrix to obtain the ellipsoid parameters.

12. The magnetic sensor of claim 10, wherein the expression of the ellipsoid model is defined by:

a₁x²+a₂y²+a₃z²+a₄xy+a₅xz+a₆yz+a₇x+a₈y+a₉z=1

wherein (x, y, z) represents a point located on the ellipsoid model, and a₁-a₉ represent the ellipsoid parameters, and the coordinate of the center of the ellipsoid model is defined by (x₀, y₀, z₀), wherein x₀, y₀ and z₀ are expressed as follows;

13. The magnetic sensor of claim 9, wherein each of the plurality of magnetic field measurements is measured along three orthogonal axes.

14. The magnetic sensor of claim 13, wherein the calibration offset is equal to a vector from an origin of the three orthogonal axes to the center of the ellipsoid model.

15. The magnetic sensor of claim 9, wherein said calibrating device comprises an element configured to subtract the calibration offset from the magnetic field measurements.