Method and apparatus for electronically rotating a heading signal

摘要

In a vehicle locating apparatus that utilizes Hall effect generators to determine the magnetic heading of the vehicle there is provided magnetic compensation by the placing of a coil around the Hall generators. A current source generator provides power to the coil of such magnitude so as to create a magnetic field which cancels the spurious local magnetic field components. The appratus also includes a set of manual switches to program a constant number into the system. The system incorporates this number to compensate for variable wheel diameters and to allow the selection of variable map scale units. This number is utilized by the system in a division technique that repeatedly subtracts the number or adds the number to the accumulated distance traveled by the vehicle. The location of the vehicle is updated as the vehicle passes a transmitting signpost. Data transmitted to and from the vehicle locating apparatus is in a self-clocking format that reduces oscillator accuracy requirements. The system also includes a second set of manual switches for inputting a rotation angle. A variable time delay circuit incorporates this rotation angle to electronically increase or decrease the measured magnetic heading angle. This electronic rotation provides for a method to correct physical misalignment of the heading sensor in the vehicle and to compensate for local magnetic deviation.