Electronic compass and method

An electronic compass comprising:

• means for generating a control signal;
• means responsive to the control signal for producing first and second reference, signals, each having the same frequentcy established by the control signal;
• first means for phase shifting the first reference signal to generate a first output signal shifted by a first phase shift which is a function of a first angle between a first direction of the first receiving and phase shifting means and the direction of the magnetic flux lines of the earth's magnetic field in a local area;
• second means for phase shifting the second reference signal to generate a-second output signal shifted by a second phase shift which is a function of a second angle between a second direction of the second receiving and phase shifting means and the direction of the magnetic flux lines of the earth's magnetic field in a local area;
• means for combining the first and second output signals to produce a third output signal shifted by a phase shift which is a function of the angle between a first reference heading of the compass and the direction of the magnetic flux lines of the earth's magnetic field in a local area;
• and
• means for monitoring the frequency o the first or second reference signal, for varying the control signal thereby to cause first and second reference signals having a predetermined frequency, and for measuring tee phase shift between the reference signal and the third output signal to calculate the angle between the heading of the compass and the direction of the magnetic flux lines of the earth's magnetic field in a local area.

An electronic compass comprising:

• a digital to analog converter for generating an analog control voltage;
• an oscillator responsive to the control voltage for producing a sine reference signal and a cosine reference signal, each having the same frequency established by the control voltage and for producing a digital reference signal in phase with and having the same frequency as the cosine reference signal;
• first circuitry for phase shifting the sine reference signal to generate a first output sinusoidal signal shifted by a first phase shift which is a function of a first angle between a first direction of the first circuitry and the direction of the magnetic flux lines of the earth's magnetic field in a local area;
• second circuitry for phase shifting the cosine reference signal to generate a second output sinusoidal signal shifted by a second phase shift which is a function of a second angle between a second direction of te second circuitry and the direction of the magnetic flux lines of the earth's magnetic field in a local area, the second direction being perpendicular to the first direction;
• circuitry for combining the first and second output sinusoidal signals to produce a third output digital signal shifted by a phase shift which is a function of the angle between a first reference heading of the compass and the direction of the magnetic flux lines of the earth's magnetic field in a local area;
• and
• a computer for monitoring the frequency of the digital reference signal, for producing and varying a digital signal connected to the digital to analog converter thereby to cause sine and cosine reference signals having a predetermined frequency, and for measuring the phase shift between the digital reference signal and the third output signal to calculate the angle between the heading of the compass and the direction of the magnetic flux lines of the earth's magnetic field in a local area.

A method of determining the angle between the heading of a compass and the direction of the magnetic flux lines of the earth's magnetic field in a local area comprising the steps of:

• generating a control signal;
• producing reference signals in response to the control signal having a frequency established by the control signal;
• phase shifting the reference signals to generate an output signal shifted by a phase shift which is a function of the angle between a reference heading of the compass and the direction of the magnetic flux lines of the earth's magnetic field in a local area;
• and
• monitoring the frequency of one of the reference signals;
• varying the control signal thereby to cause reference signals having a predetermined frequency;
• measuring the phase shift between the monitored reference signal and the output signal to calculate the angle between the heading of the compass and the direction of the magnetic flux lines of the earth's magnetic field in a local area.