Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1996-10-24
1998-06-09
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Magnetometers
33355R, 33363R, 32420713, 324225, 324247, 324260, 331 65, G01R 3302, G01B 714, G01C 2108, G05D 100
Patent
active
057640556
ABSTRACT:
An alternating bias current is made to flow through a coil wound around an MI device incorporated in an oscillation circuit, and an alternating-current bias magnetic field is applied to the MI device. An amplitude-modulated waveform corresponding to peaks which alternate between two different heights is provided at the output of the oscillation circuit in accordance with an impedance variation in the MI device according to an external magnetic field and the alternating-current bias magnetic field. The difference in height between the peaks corresponds to the strength of the external magnetic field. The output of the oscillation circuit is envelope-detected by an envelope detecting circuit, and an alternating-current component from which a direct-current component is eliminated is inputted to a comparator. The comparator provides an output signal having a digital waveform pulse-width modulated according to the difference in height between the peaks. The strength of the external magnetic field is obtained not from the absolute value of an amplitude of the output of the oscillation circuit but from a variation component in the amplitude.
REFERENCES:
patent: 3400328 (1968-09-01), Penn et al.
patent: 4182987 (1980-01-01), Moeller
patent: 4635152 (1987-01-01), Iwasaki et al.
patent: 4939459 (1990-07-01), Akachi et al.
Canon Denshi Kabushiki Kaisha
Strecker Gerard R.
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