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US5239264: Zero-offset magnetometer having coil and core sensor controlling period of an oscillator circuit

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Filing Information

Inventor(s) Timothy J. Hawks ·
Assignee(s) Precision Navigation, Inc. ·
Primary Examiner Gerard R. Strecker ·
Assistant Examiner Warren S. Edmonds ·
Application Number US7792009
Filing date 11/14/1991
Issue date 08/24/1993
Predicted expiration date 11/14/2011
U.S. Classifications 324/253  · 331/65  ·
International Classifications G01R 3304  ·
Kind CodeA
International Classifications 324244;247;249;252-256;260 ·
10 Claims, No Drawings


Abstract

A magnetometer technology is provided based on a simple axial sensor which operates using the non-linear nature of saturating magnetic core material. The sensor appears electrically as an inductor with a non-linear inductance that varies both with magnetic field applied externally and the field created by the coil current. By using this sensor as the inductor of an LR relaxation oscillator, a change in applied magnetic field will cause a change in inductance, which will in turn cause a change in the oscillator period. The period of the oscillator can be converted to a digital form by using simple counting techniques. By introducing an enhancement of this scheme whereby two different periods are measured with different oscillator characteristics, the magnetometer will have no output drift when no field is applied.

Independent Claims | See all claims (10)

  1. 1. A magnetometer for measuring an external magnetic field, comprising:a relaxation oscillator circuit comprising:driver means having an input terminal and an output terminal for providing an oscillating signal at said output terminal;sensor means having a first coil wound on a first high magnetic permeability core for controlling the period of said oscillator circuit, said first coil having first and second first-coil terminals, and said first coil being electrically symmetric between said first and second first-coil terminals;a first first-coil resistor coupled to said first first-coil terminal;a second first-coil resistor coupled to said second first-coil terminal, said second first-coil resistor and said first first-coil resistor being impedance matched;switching means coupled to said first and second first-coil terminals and to said input terminal of said driver means for coupling said input terminal alternately to said first first-coil terminal and to said second first-coil terminal; andgate means coupled to said first first-coil resistor and to said second first-coil resistor for shunting said first first-coil resistor to a DC potential when said switching means couples said input terminal of said driver means to said second first-coil terminal, and for shunting said second first-coil resistor to said DC potential when said switching means couples said input terminal of said driver means to said first first-coil terminal;measurement means for analyzing the output signal from said output terminal of said driver means, and for providing a signal representing the magnitude of said external magnetic field strength.
  2. 6. A relaxation oscillator circuit useful in a magnetometer comprising:driver means having an input terminal and an output terminal for providing an oscillating signal at said output terminal;sensor means having a first coil wound on a firs thigh magnetic permeability core for controlling the period of said oscillator circuit, said first coil having first and second first-coil terminals, and said first coil being electrically symmetric between said first and second first-coil terminals;a first first-coil resistor coupled to said first first-coil terminal;a second first-coil resistor coupled to said second first-coil terminal, said second first-coil resistor and said first first-coil resistor being impedance matched;switching means coupled to said first and second first-coil terminals and to said input terminal of said driver means for coupling said input terminal alternately to said first first-coil terminal and to said second first-col terminal;gate means coupled to said first first-col resistor and to said second first-coil resistor for shunting said first first-coil resistor to ground when said switching means couples said input terminal of said driver means to said second first-coil terminal, and for shunting said second first-coil resistor to ground when said switching means couples said input terminal of said driver means to said first first-coil terminal.
  3. 9. A magnetometer for measuring an external magnetic field, comprising:a relaxation oscillator circuit comprising:Schmitt-trigger means having an input terminal and an output terminal for providing an oscillating signal at said output terminal, said Schmitt-trigger means having symmetrical thresholds;sensor means having a first coil wound on a first high magnetic permeability core for controlling the period of said oscillator circuit, said first coil having first and second first-coil terminals, and said first coil being electrically symmetric between said first and second first-coil terminals, said sensor means being coupled between the input terminal and the output terminal of said Schmitt-trigger means;timing resistance means coupled to said input terminal of said Schmitt-trigger means; andbias polarity switching means coupled to said timing resistance means opposite said input terminal to said Schmitt-trigger means, said bias polarity switching means for switching the bias polarity of said Schmitt-trigger means;measurement means for analyzing the output signal from said output terminal of said Schmitt-trigger means, and for providing a signal representing the magnitude of said external magnetic field strength.
  4. 10.10. A relaxation oscillator circuit comprising:Schmitt-trigger means having an input terminal and an output terminal for providing an oscillating signal at said output terminal, said Schmitt-trigger means having symmetrical thresholds;sensor means having a first coil wound on a first high magnetic permeability core for controlling the period of said oscillator circuit, said first coil having first and second first-coil terminals, and said first coil being electrically symmetric between said first and second first-coil terminals, said sensor means being coupled between the input terminal and the output terminal of said Schmitt-trigger means;timing resistance means coupled to said input terminal of said Schmitt-trigger means; andbias polarity switching means coupled to said timing resistance means opposite said input terminal to said Schmitt-trigger means, said bias polarity switching means for switching the bias polarity of said Schmitt-trigger means.

References Cited

U.S. Patent Documents

Document NumberAssigneesInventorsIssue/Pub Date
US3461382 US NAVY Anderson Aug 1969
US4728888 Robert Bosch GmbH Bauer et al. Mar 1988
US4733181 Robert Bosch GmbH Bauer Mar 1988
US4851775 Precision Navigation, Incorporated Kim et al. Jul 1989
US5039945 Webb Aug 1991

Foreign Patent Documents

Document NumberAssigneesInventorsIssue/Pub Date
DE0045509Feb 1982

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