Electrical compass

Claim 2

A control circuit for use with an electrically operated magnetic field detector employing a flux-gate sensor comprising: an oscillator (25) for providing clock frequency output signals; counter means (20) coupled to said oscillator and .responsive to said clock. frequericy signals therefrom for providing an excitation frequency signal (33, 35) for a flux-gate sensor (10) and for providing a synchronization signal (36) at a harmonic frequency of said excitation frequency; bandpass filter means (40, 42) coupled to said oscillator and including means for receiving signal .information from a flux-gate sensor and.responsive to signal.information and signals from said oscillator ..to provide signals at said harmonic frequency of said excitation frequency; and detection means (50, 52) coupled to said filter means (40, 42) and to said counter means (30) and responsive to the synchronization signal and signals from said filter means for providing output signals representative of the orientation of a flux-gate sensor.to an external magnetic field.

Claim 3

A control circuit according to Claim 1 in which the bandpass filter means (40, 42) is a digital .sampled.data filter.

Claim 4

A control circuit according to Claim 1 or Claim 2 in which the harmonic frequency is the second harmonic.

Claim 5

A control circuit according to any of Claims 1 to 3 in which the.detection.means includes digital phase detection means (50., 52) having a signal input coupled to the output of said bandpass filter and having clock input means (37) coupled to said counter means for synchronizing the detection of signal information with said excitation frequency signal.

Claim 6

A control circuit according to Claim 4 in which the detection means further includes integrating means (64, 62) having input means coupled to said phase detection means for providing an analog output signal therefrom.

Claim 7

A control circuit according to Claim 5 which includes circuit means (70, 80, 90) coupled to said integrating means (64, 62) for providing a display (100) of the orientation of a flux-gate sensor.

Claim 8

A control circuit according to any of Claims 1 to 6 in which the excitation frequency-is about 400 Hz.

Claim 9

A vehicle compass system comprising: a .flux-gate magnetic sensor (10) having excitation input and signal output terminals; an oscillator (25) for providing clock frequency output signals; counter means (30) coupled to said oscillator and responsive to said clock frequency signals therefrom for providing an excitation frequency signal applied to said excitation input (33, 35) of said flux-gate sensor and for providing a synchronization signal at a harmonic frequency of said excitation frequency; bandpass filter means coupled to said oscillator and to said signal output terminals of said flux-gate sensor and.responsive to signal information from said flux-gate sensor and signals from said oscillator to pass signals therethrough at said harmonic frequency of.said excitation frequency; detection means (50, 52) coupled to said filter means and to said counter means and responsive to the synchronization signal and signals from said filter means for providing output signals representative of the orientation of a vehicle in which said flux-gate sensor is installed; and display means (100) coupled to-said detection means and responsive to said.output signals for displaying the orientation information.

Claim 10

A vehicle compass system comprising: a .flux-gate magnetic sensor (10) having excitation input and signal output terminals; an oscillator (25) for providing clock frequency output signals; counter means (30) coupled to said oscillator and responsive to said clock frequency signals therefrom for providing an excitation frequency signal applied to said excitation input (33, 35) of said flux-gate sensor and for providing a synchronization signal at a harmonic frequency of said excitation frequency; bandpass filter means coupled to said oscillator and to said signal output terminals of said flux-gate sensor and.responsive to signal information from said flux-gate sensor and signals from said oscillator to pass signals therethrough at said harmonic frequency of.said excitation frequency; detection means (50, 52) coupled to said filter means and to said counter means and responsive to the synchronization signal and signals from said filter means for providing output signals representative of the orientation of a vehicle in which said flux-gate sensor is installed; and display means (100) coupled to-said detection means and responsive to said.output signals for displaying the orientation information.

Claim 11

A system according to Claim 8 in which the said harmonic frequency is the second harmonic.

Claim 12

.10. A system according to Claim 8 or Claim 9 in which the bandpass filter means is a digital sampled data filter.

Claim 13

A system according to Claim 10 in which the detection means includes digital phase detection means having a signal output coupled to the output of said bandpass filter and having clock input means coupled to said counter means for synchronizing the detection of signal information with said excitation frequency signal.

Claim 14

A system according to Claim 10 in which the detection means further includes integrating means (64,.62) having input means coupled to said phase detection means for providing an analog output signal therefrom.