Monitoring accuracy of an electronic compass

• US 6,539,639 B2
• Filed: 12/06/2000
• Issued: 04/01/2003
• Est. Priority Date: 12/06/2000
• Status: Expired due to Term

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Smith, Robert B.
• Primary Examiner(s): Gutierrez, Diego
• Assistant Examiner(s): Jagan, Mirellys
• Application Number:
  US09/731,516
• Publication Number:
  US 20020092188A1
• Time in Patent Office: 846 Days
• Field of Search: 333/56, 333/57, 333/55.R, 333/19, 333/26, 702/92, 702/150
• US Class Current: 33/356
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

A three-axis physical model is used to numerically compensate for errors in measured magnetic field values in an electronic compass for operation at any orientation. This compensation method generates certain quantities that characterize the magnetic field of the Earth in the vertical plane. These quantities are used to monitor the accuracy of the electronic compass during normal operation by comparing their current values either with values obtained during the calibration procedure or with values obtained from historical averages. Significant departure from the calibration values or from the historical averages indicates a probable loss of accuracy of the compass, and the user is so alerted.

Claims

1. A method of monitoring the accuracy of an electronic compass, the method comprising:

during a calibration operation of the electronic compass, calculating a plurality of compensation coefficient values using a technique that also yields a first set of two magnetic field values that characterize the magnetic field of the Earth during the calibration operation;

during a normal operation of the electronic compass, calculating subsequent compass magnetic azimuth values that yield a second set of two magnetic field values that characterize the magnetic field of the Earth during the normal operation;

comparing at least one of the first magnetic field values with at least one of the second magnetic field values;

comparing a first vector derived from the first magnetic field values with a second vector derived from the second magnetic field values; and

comparing a magnitude of a vector difference between the first and second vectors with a threshold magnitude to determine the accuracy of the compass.

2. The method of claim 1, wherein the first set of two magnetic field values and the second set of two magnetic field values both characterize the magnetic field of the Earth in a vertical plane.

3. The method of claim 1, further comprising comparing a vertical component of the Earth'"'"'s magnetic field calculated during the calibration operation with a vertical component of the Earth'"'"'s magnetic field calculated during the normal operation.

4. The method of claim 1, further comprising comparing a level component of the Earth'"'"'s magnetic field calculated during the calibration operation with a level component of the Earth'"'"'s magnetic field calculated during the normal operation.

5. The method of claim 1, further comprising comparing a magnitude of the first vector a magnitude of the second vector.

6. The method of claim 1, further comprising comparing an angle of the first vector with an angle of the second vector.

7. The method of claim 1, further comprising comparing at least one of the first magnetic field values with at least one of the second magnetic field values with reference to a plurality of threshold values.

8. The method of claim 7, further comprising alerting a user of the electronic compass in response to a difference between the compared magnetic field values exceeding one of the threshold values.

9. The method of claim 8, further comprising selecting an alert to be conveyed to the user as a function of which one of the plurality of threshold values is exceeded by the difference between the compared magnetic field values.

10. A method of monitoring the accuracy of an electronic compass, the method comprising:

during operation of the electronic compass, calculating a compass magnetic azimuth using a technique that also yields a plurality of magnetic field values that characterize the magnetic field of the Earth during the compass operation;

maintaining a historical average of the magnetic field values;

comparing at least one of the magnetic field values with the historical average;

comparing a first vector derived from the magnetic field values with a second vector derived from the historical average; and

comparing a magnitude of a vector difference between the first and second vectors with a threshold magnitude to determine the accuracy of the compass.

11. The method of claim 10, wherein the plurality of magnetic field values characterize the magnetic field of the Earth in a vertical plane.

12. The method of claim 10, further comprising comparing a vertical component of the Earth'"'"'s magnetic field calculated during the operation of the electronic compass with a historical average of the vertical component of the Earth'"'"'s magnetic field maintained during the normal operation.

13. The method of claim 10, further comprising comparing a level component of the Earth'"'"'s magnetic field calculated during the operation of the electronic compass with a historical average of the level component of the Earth'"'"'s magnetic field maintained during the normal operation.

14. The method of claim 10, further comprising comparing a magnitude of the first vector with a magnitude of the second vector.

15. The method of claim 10, further comprising comparing an angle of the first vector with an angle of the second vector.

16. The method of claim 10, further comprising comparing at least one of the magnetic field values with the historical average with reference to a plurality of threshold values.

17. The method of claim 16, further comprising alerting a user of the electronic compass in response to a difference between the compared magnetic field values and the historical average exceeding one of the threshold values.

18. The method of claim 17, further comprising selecting an alert to be conveyed to the user as a function of which one of the plurality of threshold values is exceeded by the difference between the compared magnetic field values and the historical average.