Method and system for electronic compass calibration and verification

• US 7,154,267 B2
• Filed: 01/07/2005
• Issued: 12/26/2006
• Est. Priority Date: 01/07/2005
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Withanawasam, Lakshman S.
• Primary Examiner(s): LEDYNH, BOT L
• Application Number:
  US11/031,940
• Publication Number:
  US 20060152217A1
• Time in Patent Office: 718 Days
• Field of Search: 324/244, 333/55.R
• US Class Current: 324/244
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

A method and system for calibrating a magnetic compass and/or verifying a compass calibration, using a calibration magnetic field produced by a field-generating coil within the magnetic compass is described. The field-generating coil is located near magnetometers within the magnetic compass. Passing a self-trimming current through the coil produces a magnetic field that acts on the magnetometers. Samples of an output signal from each magnetometer are taken to obtain digital values that indicate the output signal from each magnetometer. The digital values are used by a processor to determine one or more calibration coefficient for using calibrating the magnetic compass. The samples of the output signals are taken when a self-trimming current is passing through the coil and when the self-trimming current is not passing through the coil. Calibration of the compass occurs by applying the one or more calibration coefficients to subsequent signals that indicate the output signals of one or more of the magnetometers.

Claims

1. A system comprising:

a first magnetometer that produces a first output signal;

a second magnetometer that produces a second output signal;

an analog-to-digital signal converting means coupled to the first and second magnetometers, wherein the analog-to-digital signal converting means converts (i) the first output signal to a first digital signal, and (ii) the second output signal to a second digital signal;

a processor that receives the first digital signal and the second digital signal; and

a network that includes a coil located in proximity to the first and second magnetometers, wherein (i) the network is coupled to the processor, (ii) the processor provides a first voltage signal at the network for producing a first self-trimming current, and (iii) the coil generates a magnetic field in the vicinity of the first and second magnetometers when the first self-trimming current passes through the coil.

2. The system of claim 1, further comprising data storage for storing program instructions executable by the processor, wherein the program instructions comprise (i) one or more instructions for computing a calibration coefficient, and (ii) one or more instructions for applying the calibration coefficient to trim at least one of the first and second digital signals.

3. The system of claim 2, wherein the one or more instructions for computing the calibration coefficient include (i) an instruction to read values of the first and second digital signals when the first self-trimming current is passing through the network in order to obtain a first digital value and a second digital value, respectively, (ii) an instruction to read values of the first and second digital signals when the first self-trimming current is not passing through the network in order to obtain a third digital value and a fourth digital value, respectively, and (iii) an instruction to divide the absolute value of the difference of the first digital value and the third digital value by the absolute value of the difference of the second digital value and the fourth digital value.

4. The system of claim 3, wherein the one or more instructions for applying the calibration coefficient include an instruction to multiply at least one of the first and second digital signals by the calibration coefficient.

5. The system of claim 1, wherein the processor comprises a first port, the network is coupled to the processor at the first port, and the processor provides the first voltage signal at the first port.

6. The system of claim 5, wherein the network further comprises an impedance having first and second ends, wherein the coil has first and second ends, wherein the first end of the impedance is coupled to the first port, wherein the second end of the impedance is coupled to the first end of the coil, and wherein the second end of the coil is coupled to an electrical ground.

7. The system of claim 6, wherein the impedance is a resistor.

8. The system of claim 5, wherein (i) the processor further comprises a second port, and provides a second voltage at the network for producing a second self-trimming current, and (ii) the coil generates a second magnetic field in the vicinity of the first and second magnetometers when the second self-trimming current passes through the coil.

9. The system of claim 8, wherein the network further comprises first and second impedances each having respective first and second ends, wherein the coil has first and second ends, wherein the first end of the first impedance is coupled to the first port and to the first end of the coil, wherein the first end of the second impedance is coupled to the second port and to the second end of the coil, and wherein the second ends of the first and second impedances are coupled to an electrical ground.

10. The system of claim 9, wherein the first and second impedances are resistors.

11. The system of claim 8, wherein the network further comprises first, second, and third impedances each having respective first and second ends, wherein the coil has first and second ends, wherein the first end of the first impedance is coupled to the first port and to the first end of the coil, wherein the first end of the second impedance is coupled to the second end of the coil and to the first end of the third impedance, wherein the second end of the third impedance is coupled to the second port, and wherein the second ends of the first and second impedances are coupled to an electrical ground.

12. The system of claim 11, wherein the first, second, and third impedances are resistors.

13. The system of claim 1, further comprising:

an amplification means for (i) amplifying the first output signal before the analog-to-digital converter converts the first output signal to the first digital signal, and (ii) amplifying the second output signal before the analog-to-digital converter converts the second output signal to the second digital signal.

14. The system of claim 1, further comprising:

a third magnetometer that (i) produces a third output signal, (ii) is coupled to the analog-to-digital converting means, and (iii) is located in proximity to the coil, wherein the analog-to-digital converting means converts the third output signal to a third digital signal, the processor receives the third digital signal, and the magnetic field is in the vicinity of the third magnetometer; and

data storage for storing program instructions executable by the processor, wherein the program instructions comprise (i) one or more instructions for computing one or more calibration coefficients, and (ii) one or more instructions for applying the one or more calibration coefficients to trim one or more of the first, second, and third digital signals.

15. A system comprising:

a first magnetometer that produces a first output signal;

a second magnetometer that produces a second output signal;

a first amplifier coupled to the first magnetometer for receiving the first output signal, wherein the first amplifier amplifies the first output signal to produce a first amplifier signal;

a second amplifier coupled to the second magnetometer for receiving the second output signal, wherein the second amplifier amplifies the second output signal to produce a second amplifier signal;

an analog-to-digital converter coupled to the first and second amplifiers, wherein the analog-to-digital converter converts the first amplifier signal to a first digital signal and coverts the second amplifier signal to a second digital signal;

a processor that receives the first and second digital signals; and

a network that includes a coil located in proximity to the first and second magnetometers, wherein (i) the network is coupled to the processor, (ii) the processor provides a voltage signal for producing a first self-trimming current, and (iii) the coil generates a magnetic field in the vicinity of first and second magnetometers when the first self-trimming current passes through the coil.

16. The system of claim 15, further comprising data storage for storing program instructions executable by the processor, wherein the program instructions comprise (i) one or more instructions for computing one or more calibration coefficients, and (ii) one or more instructions for applying the one or more calibration coefficients to trim at least one of the first and second digital signals.

17. The system of claim 16, wherein the one or more instructions for computing the one or more calibration coefficients include (i) an instruction to read values of the first and second digital signals when the first self-trimming current is passing through the network in order to obtain a first digital value and a second digital value, respectively, (ii) an instruction to read values of the first and second digital signals when the first self-trimming current is not passing through the network in order to obtain a third digital value and a fourth digital value, respectively, and (iii) an instruction to divide the absolute value of the difference of the first digital value and the third digital value by the absolute value of the difference of the second digital value and fourth digital value.

18. The system of claim 16, wherein the one or more instructions for applying the calibration coefficient include an instruction to multiply at least one of the first and second digital signals by one of the one or more calibration coefficients.

19. The system of claim 15, wherein the processor comprises a first port, the network is coupled to the processor at the first port, and the processor provides the first voltage signal at the first port.

20. The system of claim 19, wherein the network further comprises an impedance having first and second ends, wherein the coil has first and second ends, wherein the first end of the impedance is coupled to the first port, wherein the second end of the impedance is coupled to the first end of the coil, and wherein the second end of the coil is coupled to an electrical ground.

21. The system of claim 19, wherein (i) the processor further comprises a second port, and provides a second voltage signal at the network for producing a second self-trimming current, and (ii) the coil generates a second magnetic field in the vicinity of the first and second magnetometers when the second self-trimming current passes through the coil.

22. The system of claim 21, wherein the network further comprises first and second impedances each having respective first and second ends, wherein the coil has first and second ends, wherein the first end of the first impedance is coupled to the first port and to the first end of the coil, wherein the first end of the second impedance is coupled to the second port and to the second end of the coil, and wherein the second ends of the first and second impedances are coupled to an electrical ground.

23. The system of claim 21, wherein the network further comprises first, second, and third impedances each having respective first and second ends, wherein the coil has first and second ends, wherein the first end of the first impedance is coupled to the first port and to the first end of the coil, wherein the first end of the second impedance is coupled to the second end of the coil and to the first end of the third impedance, wherein the second end of the third impedance is coupled to the second port, and wherein the second ends of the first and second impedances are coupled to an electrical ground.

24. A magnetic compass comprising:

a first magnetometer that produces a first output signal;

a second magnetometer that produces a second output signal;

an amplification means coupled to the first magnetometer and the second magnetometer, wherein the amplification means (i) receives and then amplifies the first output signal to produce a first amplifier signal, and (ii) receives and then amplifies the second output signal to produce a second amplifier signal;

an analog-to-digital signal converting means coupled to the amplification means, wherein the analog-to-digital signal converting means (i) receives and then converts the first amplifier signal to a first digital signal, and (ii) receives and then converts the second amplifier signal to a second digital signal;

a processor that receives the first and second digital signals; and

a network that includes a coil located in proximity to the first and second magnetometers, wherein (i) the network is coupled to the processor, (ii) the processor provides a voltage signal at the network for producing a first self-trimming current, and (iii) the coil generates a magnetic field in the vicinity of the first and second magnetometers when the first self trimming current passes through the coil.

25. The magnetic compass of claim 24, further comprising data storage for storing program instructions executable by the processor, wherein the program instructions include (i) one or more instructions for computing at least one calibration coefficient, and (ii) one or more instructions for applying the at least one calibration coefficient to trim at least one compass signal produced by the compass.

26. The magnetic compass of claim 24, further comprising:

a third magnetometer that (i) produces a third output signal, (ii) is coupled to the amplification means, and (iii) is located in proximity to the coil, wherein the amplification means receives and then amplifies the third output signal to produce a third amplifier signal, the analog-to-digital signal converting means receives and then converts the third amplifier signal to a third digital signal, and the processor receives the third digital signal; and

data storage for storing program instructions executable by the processor, wherein the program instructions include (i) one or more instructions for computing one or more calibration coefficients based on values of the first, second and third digital signals received at the processor when the first self-trimming current is passing through the coil and values of the first, second, and third digital signals received at the processor when the first self-trimming current is not passing through the coil, and (ii) one or more instructions for applying the one or more calibration coefficients to trim one or more compass signals produced by the compass.

27. In a magnetic compass that includes a processor, a coil coupled to the processor, at least first and second magnetometers, and an analog-to-digital signal converting means that converts at least a first analog signal produced by the first magnetometer to a first digital signal and a second analog signal produced by the second magnetometer to a second digital signal, a method of calibrating the magnetic compass comprising:

driving the coil with a first voltage supplied by a first processor output so as to supply a first self-trimming current through the coil;

reading values of the first and second digital signals, at the processor when driving the coil with the first voltage, to obtain a first digital value and a second digital value, respectively;

reading values of the first and second digital signals, at the processor when not driving the coil with the first voltage, to obtain a third digital value and a fourth digital value, respectively; and

determining a first calibration coefficient based on the first digital value, the second digital value, the third digital value, and the fourth digital value, for use in trimming at least one of the first and second digital signals.

28. The method of claim 27, wherein driving the coil with the first voltage to supply the first self-trimming current through the coil causes the coil to generate a first magnetic field in the vicinity of the first magnetometer and the second magnetometer, wherein the first magnetic field causes the first analog signal and the second analog signals to change in value.

29. The method of claim 27, wherein determining the first calibration coefficient involves the processor executing at least a first program instruction for determining a first calibration coefficient, wherein the at least a first program instruction includes an instruction to divide an absolute value of a difference between the first digital value and the third digital value by an absolute value of a difference between the second digital value and the fourth digital value.

30. The method of claim 29, further comprising adjusting at least one of the first and second digital signals, wherein adjusting the at least one of the first and second digital signals comprises the processor executing at least a second program instruction, wherein the at least a second program instruction includes an instruction to multiply at least one of the first and second digital signals by the first calibration coefficient.

31. The method of claim 30, further comprising verifying the step of determining the first calibration coefficient, wherein the verifying comprises:

driving the coil with a second voltage supplied by a second processor output so as to supply a second self-trimming current through the coil;

reading values of the first and second digital signals, at the processor when driving the coil with the second voltage, to obtain a fifth digital value and a sixth digital value, respectively;

determining a second calibration coefficient based on the first digital value, the second digital value, the fifth digital value, and the sixth digital value; and

comparing the first calibration coefficient to the second calibration coefficient.

32. The method of claim 31, wherein determining the second calibration coefficient involves the processor executing at least a third program instruction for determining the second calibration coefficient, wherein the at least a third program instruction includes an instruction to divide an absolute value of a difference between the first digital value and the fifth digital value by an absolute value of a difference between the second digital value and the sixth digital value.

33. The method of claim 31, wherein driving the coil with the second voltage to supply the second self-trimming current through the coil causes the coil to generate a second magnetic field in the vicinity of the first magnetometer and the second magnetometer, wherein the second magnetic field causes the first analog signal and the second analog signal to change in value.

34. The method of claim 27, further comprising supplying the first analog signal from the first magnetometer and the second analog signal from the second magnetometer, to an amplification means for amplification of the first analog signal and the second analog signal prior to supplying the first analog signal and the second analog signal to the analog-to-digital signal converting means.