Low power, high accuracy magnetometer and magnetic field strength measurement method
First Claim
1. A magnetometer, comprising:
- (a) a core of magnetic material;
(b) drive means for periodically applying a control magnetic field to said core to saturate said core;
(c) a first sense coil magnetically coupled to said core; and
(d) first sense circuit means connected to said first sense coil for providing a sense signal representative of the current in said first sense coil, said first sense circuit means comprising an operational amplifier having an inverting input and an output which produces said sense signal and a feedback path from sad output to said inverting input so as to render said inverting input a virtual ground, said first sense coil being connected to said inverting input.
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Abstract
A magnetometer and method for measuring magnetic field strength particularly adapted for use in an electronic flux gate compass. A core of magnetic material in the shape of a toroid is coupled to a drive coil and to two sense coils oriented along orthogonal axes. A current limited, current source coupled to the drive coil periodically saturates the core, drives the core out of saturation at an intermediate current level, and saturates the core again. Each sense coil is coupled to a sense circuit which measures the current in the sense coil induced by the periodically changing flux density in the coil resulting from an external magnetic field coupled to the sense coil, produces a dc feedback signal to cancel out the external magnetic field, and provides the dc signal as an output representative of the external magnetic field strength along the axis of the sense coil. The dc signal is produced by synchronously detecting the amplified ac current in the sense coil. Low pass filters are provided to eliminate ac components from the magnetometer output.
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Citations
26 Claims
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1. A magnetometer, comprising:
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(a) a core of magnetic material; (b) drive means for periodically applying a control magnetic field to said core to saturate said core; (c) a first sense coil magnetically coupled to said core; and (d) first sense circuit means connected to said first sense coil for providing a sense signal representative of the current in said first sense coil, said first sense circuit means comprising an operational amplifier having an inverting input and an output which produces said sense signal and a feedback path from sad output to said inverting input so as to render said inverting input a virtual ground, said first sense coil being connected to said inverting input. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A magnetometer, comprising:
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(a) a core of magnetic material; (b) drive means for periodically applying a control magnetic field to said core to saturate said core; (c) a first sense coil majestical coupled to said core; and (d) first sense circuit means connected to said first sense coil for providing a sense signal representative of the current in said first sense coil, said first sense circuit means including means for providing to said first sense coil a load impedance of substantially zero.
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10. A magnetometer, comprising:
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(a) a core of magnetic material; (b) drive means for periodically applying a control magnetic field to said core to saturate said core; (c) first sense coil magnetically coupled to said core; and (d) first sense circuit means connected to said first sense coil for providing a sense signal representative of the current in said first sense coil, said first sense circuit means including means for providing a load impedance to said first sense coil, the time constant of said first sense coil and said load impedance together being much greater than the time of application of said control magnetic field to said core. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A method for determining the strength of a magnetic field in a given direction, comprising the steps of:
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(a) periodically saturating and unsaturating a core of magnetic material placed in said magnetic field by magnetically coupling a drive coil to said core and periodically applying to said drive coil a drive current first sufficient to saturate said core in one direction, then a current in the opposite direction sufficient to take said core out of saturation and nearly to saturation in said opposite direction, and thereafter a current sufficient to saturate said core in said opposite direction, said core having a first sense coil magnetically coupled thereto; and (b) measuring the current induced in said first sense coil by said magnetic field and providing a first sense signal representative of the amplitude of said current, said amplitude being indicative of the strength of said magnetic field.
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18. A method for determining the strength of a magnetic field in a given direction, comprising the stpes of:
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(a) periodically saturating and unsaturating a core of magnetic material placed in said magnetic field, said core having a first sense coil magnetically coupled thereto; (b) connecting said first sense coil to a load impedance of substantially zero; and (c) measuring the current in said first sense coil and providing a first sense signal representative of the amplitude of said current, said amplitude being indicative of the strength of said magnetic field.
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19. A method for determining the strength of a magnetic field in a given direction, comprising the steps of:
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(a) periodically saturating and unsaturating a core of magnetic material placed in said magnetic field, said core having a first sense coil magnetically coupled thereto; (b) connecting said first sense coil to an operational amplifier having an inverting input and an output which provides said first sense signal, and a feedback path from said output to said inverting input so as to render said inverting input a virtual ground, said first sense coil being connected to said inverting input; and (c) measuring the current in said first sense coil and providing a first sense signal representative of the amplitude of said current, said amplitude of said current being indicative of the strength of said magnetic field. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26)
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Specification