Compensation system for electronic compass
First Claim
1. A method for compensating for the effect of a deviating magnetic field in a vehicle compass, said compass comprising:
- first and second magnetoresistive sensors responsive to an external magnetic field for developing electronic signals representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said first and second sensors being oriented in a predetermined angular relation with each other, and being aligned in a predetermined angular relation with respective axes of said vehicle, each of said sensors including means for nullifying at least part of a deviating magnetic field which impinges on it, said method comprising the steps of;
determining-whether the value of the sensor signal of each sensor is different from a nominal value which corresponds approximately to the value of the earth magnetic field, if it is, using said nullifying means for adjusting the magnetic field impinging on each sensor to adjust the sensor signal to a value approximately equal to the nominal value, determining the maximum and minimum peak values of each sensor signal, determining the average of said peak values of each sensor signal, and mathematically compensating the actual value of each sensor signal in accordance with the respective average value.
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Accused Products
Abstract
An electronic compass is described for use in vehicles. The compass employs a magnetoresistive sensor for sensing the earth magnetic field and the sensor is operated in alternate set/reset bias modes. In a first embodiment, the compass is provided with deviation compensation by a closed loop system including measurement of the sensor output signals and an offset current strap for nullifying the vehicle deviation field. In a second embodiment, deviation compensation is provided by operation in an initial calibration mode and by operation in a normal compensation mode to adjust compensation, as needed, on a long term basis during normal operation of the compass. In the initial calibration mode, while the vehicle is being driven, the signal peak values are adjusted to a nominal earth field level by changing the offset current. Then, compensating signal reference values for each axis are determined as each peak for that axis is determined. The system automatically exits the initial calibration mode when certain criteria have been met. In the normal compensation mode, The signal reference value for each axis is adjusted at least once during the time interval between turn-on and turn-off of the vehicle ignition switch.
22 Citations
12 Claims
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1. A method for compensating for the effect of a deviating magnetic field in a vehicle compass, said compass comprising:
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first and second magnetoresistive sensors responsive to an external magnetic field for developing electronic signals representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said first and second sensors being oriented in a predetermined angular relation with each other, and being aligned in a predetermined angular relation with respective axes of said vehicle, each of said sensors including means for nullifying at least part of a deviating magnetic field which impinges on it, said method comprising the steps of;
determining-whether the value of the sensor signal of each sensor is different from a nominal value which corresponds approximately to the value of the earth magnetic field, if it is, using said nullifying means for adjusting the magnetic field impinging on each sensor to adjust the sensor signal to a value approximately equal to the nominal value, determining the maximum and minimum peak values of each sensor signal, determining the average of said peak values of each sensor signal, and mathematically compensating the actual value of each sensor signal in accordance with the respective average value.
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2. A method for compensating for the effect of a deviating magnetic field in a vehicle compass, said compass comprising:
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first and second magnetoresistive sensors responsive to an external magnetic field for developing electronic signals representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said first -and second sensors being oriented in a predetermined angular relation with each other, and being aligned in a predetermined angular relation with respective axes of said vehicle, each of said sensors including means for nullifying at least part of a deviating magnetic field which impinges on it, a digital electronic circuit including means for measuring said signals when said signals are within a predetermined measurement range, said method comprising the steps of;
determining whether the value of the sensor signal of each sensor is within said measurement range, if it is not, using said nullifying means for nullifying at least part of magnetic field impinging on said sensor to reduce the sensor signal to a value within said range. - View Dependent Claims (3, 4)
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5. A method for updating the deviation compensation of a vehicle compass comprising:
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first and second sensors responsive to an external magnetic field for developing electronic signals representative of said external magnetic field, said external magnetic field being a combination of the earth magnetic field and a deviating field of the vehicle, said first and second sensors being oriented in a predetermined angular relation with each other, and being aligned in a predetermined angular relation with respective axes of said vehicle, and a memory which stores a reference value for each sensor signal, said reference value for each sensor being equal to an offset value for providing deviation compensation for the respective sensor at a previous time, said method comprising the steps of;
detecting the occurrence of a peak in the sensor signal of one of the sensors, measuring the value of the sensor signal of the other sensor which occurs at the same time as the occurrence of said peak, and if there is a difference between the measured value and said reference value, adjusting the reference value in accordance with the difference. - View Dependent Claims (6, 7)
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8. A method of determining an offset calibration value for a magnetoresistive sensor in a magnetic compass, said compass including an electronic circuit and a microcomputer for processing an output signal from said sensor, said sensor being alternately biased between a reset mode and a set mode,
said method comprising the steps of: -
determining whether both reset signal and the set signal are equal to or greater than zero at the same time, if they are, calculate a sensor offset calibration value. - View Dependent Claims (9)
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10. A method for compensating an electronic compass in a vehicle of the type comprising first and second sensors oriented in a predetermined angular relation with each other and with respective axes of the vehicle,
said method comprising the steps of: -
determining a compensating reference signal value for each sensor, detecting the occurrence of a peak in the sensor signal of one of the sensors, measuring the value of the sensor signal of the other sensor which occurs at the same time as the occurrence of said peaks, and, if there is a difference between the measured value and the reference value, adjusting the reference value in accordance with the difference.
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11. In combination, for use in a vehicle,
an electronic compass comprising a magnetoresistive sensor for detecting the magnetic field of the earth, an electronic circuit coupled with said sensor for developing signals indicative of the direction of said vehicle, and electronic display coupled with said circuit for displaying said direction, a rear view mirror, said electronic display being disposed on said mirror for viewing by a driver of said vehicle.
Specification