| 摘要 |
PURPOSE:To make it possible to detect azimuth accurately, by decreasing and increasing the amplification factor of an AC signal amplifier, in correspondence with the magnitude of a magnetic field component, which is not related to the azimuth of a vehicle. CONSTITUTION:A sensor 2 is of a fluxgate type. An exciting coil 14 is applied to a part of an annular core 13. Both ends of the coil 14 are connected to an oscillator 15. The coil is excited by an AC signal. An output coil 10 is provided in the direction of one diameter of the core 13. A coil 11 is provided in the direction perpendicular to said diameter. The coil 10 is arranged in the x axis and the advancing direction of a vehicle. The sensor 2 is saturated by an exciting frequency. Distorted waveforms are generated in the coils 10 and 11. The amplitude of the second harmonic waves of said waveforms is proportional to a DC magnetic field which is applied to the sensor 2. When the magnetizing component becomes large, a resistor 36 is connected in parallel with a resistor 34, and the amplification factor of an operation amplifier 40 is decreased. The output signal of the amplifier 40 is inputted to a sample and hold circuit 60. The amagnetic field component, which is obtained by changing the sample and held peak value into a DC level, is converted into digital value. The value is inputted to a computer system 63. When the magnetizing amount is larger than the specified amount, a signal, which turns ON switches 50 and 51, is sent out, and the amplification factor is decreased. |
