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Method and apparatus for automatic calibration of magnetic compass

  • US 4,797,841 A
  • Filed: 07/02/1986
  • Issued: 01/10/1989
  • Est. Priority Date: 11/28/1983
  • Status: Expired due to Term
First Claim
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1. Apparatus for calibrating the distortions in the readings of a magnetic compass having a plurality of windings in a two dimensional plane and mounted in a vehicle comprising:

  • first means coupled to the compass windings for obtaining the outputs from each of the windings as a function of time by weighting and combining the outputs from each of the windings at a first time and for a predetermined number of the next previous times to said first time to obtain a time filtered output for each of the windings;

    second means coupled to said first means to form from said windings outputs measurement parameters having sensitivity values;

    said sensitivity values being variables in a generalized equation that represents the configuration and location of a geometrical figure defined by the locus of coordinates of said outputs, said outputs having distortions due to permanent and induced magnetism of the vehicle and distortions due to winding imbalance between the misorientation of the magnetic compass windings;

    said second means for defining calibration coefficients of said measurement parameters in said equation;

    third means coupled to said second means to incorporate said measurement parameters and said calibration coefficients into a least squares matrix and to solve for said calibration coefficients;

    fourth means coupled to said third means for computing calibration parameters from said calibration coefficients that are to be applied to said outputs;

    fifth means coupled to said first means and said fourth means for applying said calibration parameters to said outputs from said first means to form an output from each of two windings;

    said two windings being orthogonally related to one another;

    sixth means coupled to said fifth means for obtaining the calibrated compass heading from said two windings outputs.

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