Method of calibrating a compass heading

Claim 1

A method of calibrating compass heading θ for a compass comprising a magnetometer having means for sensing horizontal components as independent output signals Hx and Hy and means for sensing the vertical component providing a corresponding Hz output signal, the method comprising the steps of: applying a first magnetic field representative of the earth's magnetic field at a first latitude; storing the Hx, Hy and Hz signals corresponding to said first magnetic field; applying a second magnetic field representative of the earth's magnetic field at a second latitude; storing the Hx, Hy and Hz signals corresponding to said second magnetic field; providing the difference between the different stored instances of Hx, Hy and Hz as dHx, dHy and dHz signals, respectively; calculating a first error coefficient signal P according to dHx/dHz; calculating a second error coefficient signal R according to dHy/dHz; and adding the error coefficients P and R to the calculation of the cosine and sine of the heading angle, wherein the corrected heading angle is computed as: ##EQU1## wherein Hxm is Hx measured, Hym is Hy measured, Hx' is the actual x horizontal component of the earth's field, and Hz' is the actual vertical component of the earth's field.

Claim 2

A method of calibrating compass heading θ for a compass comprising a magnetometer having means for sensing horizontal components as independent output signals Hx and Hy and means for sensing the vertical component providing a corresponding Hz output signal, the method comprising the steps of: applying a first magnetic field representative of the earth's magnetic field at a first latitude; storing the Hx, Hy and Hz signals corresponding to said first magnetic field; applying a second magnetic field representative of the earth's magnetic field at a second latitude; storing the Hx, Hy and Hz signals corresponding to said second magnetic field; providing the difference between the different stored instances of Hx, Hy and Hz as dHx, dHy and dHz signals, respectively; calculating a first error coefficient signal P according to dHx/dHz; calculating a second error coefficient signal R according to dHy/dHz; and adding the error coefficients P and R to the calculation of the cosine and sine of the heading angle, wherein the corrected heading angle is computed as: ##EQU1## wherein Hxm is Hx measured, Hym is Hy measured, Hx' is the actual x horizontal component of the earth's field, and Hz' is the actual vertical component of the earth's field.

Claim 5

A method of calibrating compass heading θ for a compass comprising a magnetometer having means for sensing horizontal components as independent output signals Hx and Hy and means for sensing the vertical component providing a corresponding Hz output signal, the method comprising the steps of: applying a first magnetic field representative of the earth's magnetic field at a first latitude; storing the Hx, Hy and Hz signals corresponding to said first magnetic field; applying a second magnetic field representative of the earth's magnetic field at a second latitude; storing the Hx, Hy and Hz signals corresponding to said second magnetic field; providing the difference between the difference stored instances of Hx, Hy and Hz as dHx, dHy and dHz signals, respectively; calculating a first error coefficient signal P according to dHx/dHz; calculating a second error coefficient signal R according to dHy/dHz; and adding the error coefficients P and R to the calculation of the cosine and sine of the heading angle producing the following H vector output signals: Hx(corrected)=Hx' cos θ+Hz' sin P Hy(corrected)=Hy' cos θ+Hz' sin R, wherein Hx' is the actual x horizontal component of the earth's field, Hy' is the actual y horizontal component of the earth's field, and Hz' is the actual z vertical component of the earth's field.

Claim 6

A method of calibrating compass heading θ for a compass comprising a magnetometer having means for sensing horizontal components as independent output signals Hx and Hy and means for sensing the vertical component providing a corresponding Hz output signal, the method comprising the steps of: applying a first magnetic field representative of the earth's magnetic field at a first latitude; storing the Hx, Hy and Hz signals corresponding to said first magnetic field; applying a second magnetic field representative of the earth's magnetic field at a second latitude; storing the Hx, Hy and Hz signals corresponding to said second magnetic field; providing the difference between the difference stored instances of Hx, Hy and Hz as dHx, dHy and dHz signals, respectively; calculating a first error coefficient signal P according to dHx/dHz; calculating a second error coefficient signal R according to dHy/dHz; and adding the error coefficients P and R to the calculation of the cosine and sine of the heading angle producing the following H vector output signals: Hx(corrected)=Hx' cos θ+Hz' sin P Hy(corrected)=Hy' cos θ+Hz' sin R, wherein Hx' is the actual x horizontal component of the earth's field, Hy' is the actual y horizontal component of the earth's field, and Hz' is the actual z vertical component of the earth's field.