Vehicle compass with automatic continuous calibration

An electrical compass system for use in a vehicle such as an automobile comprising:

• sensing means for detecting the earth's magnetic field and for providing electrical signals representing the direction of the vehicle in relation to the earth's magnetic field;
• circuit means for processing said signals and for providing display output signals in response thereto;
• display means coupled to said circuit means and responsive to said display output signals for displaying the vehicle heading;
• and
• said circuit means including first determining means responsive to said sensing means for determining that the vehicle has been moved through a closed loop, second determining means responsive to said first determining means and said direction representative signals for determining during the course of movement of the vehicle through a closed loop, the maximum and minimum detected signal level from said sensing means corresponding to the effect of the earth's magnetic field and the magnetic properties of the vehicle on said sensing means;
• said circuit means further including means for calculating from said maximum and minimum detected signal level an offset signal representing the static flux field due to the vehicle magnetism and means for correcting said display output signals to display the vehicle heading.

A digital compass system for a vehicle comprising:

• a magnetic field sensor;
• a microprocessor and interface circuit means coupling said microprocessor to said sensor for providing display output signals representative of the magnetic direction of orientation of said sensor;
• display means coupled to said microprocessor for displaying said magnetic direction;
• and
• wherein said microprocessor is programmed to provide means for compensating said output signals for local magnetic field interference which otherwise causes said sensor to provide output signals which deviate from the actual magnetic orientation of said sensor with respect to the earth's magnetic field such that the actual magnetic orientation of said sensor will be displayed, said compensating means including means for continuously monitoring signal information from said sensor circuit as the vehicle travels during use, for determining that the vehicle has traveled through a closed loop and, after each completed loop of travel of the vehicle, for determining an updated correction to the sensed field, said compensating means further including means responsive to said updated correction for modifying the signal applied to said display means to correct for the local field interference.

An electrical compass system for use in a vehicle such as an automobile comprising:

• sensing means for detecting the earth's magnetic field and for providing electrical signals representing the direction of the vehicle in relation to the earth's magnetic field;
• circuit means for processing said signals and for providing display output signals during a period of time in which the vehicle travels through a closed loop circumscribing 365.degree. of movement in one direction;
• display means coupled to said circuit means and responsive to said display output signals for displaying the vehicle heading;
• means for determining that the vehicle has moved through a closed loop, means for determining, during the course of movement of the vehicle through the closed loop, the maximum and minimum detected signal level from said sensing means corresponding to the effect of the earth's magnetic field and the magnetic properties of the vehicle on said sensing means;
• said circuit means including means for calculating from the signal information during each completed loop of travel of the vehicle, an offset signal representing the static flux field due to the vehicle magnetism and for correcting the display output signals to display the vehicle heading;
• and
• said circuit means further including means for detecting the rate of change of said direction representative signals to determine if the rate of change exceeds a predetermined level thereby indicating the existence of invalid detected direction information and for providing an error output signal for display in the event the rate of change exceeds said predetermined level.