# US 4,398,352 A · Compensated magnetic sensor for use on highly magnetized vehicles

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- Number: US 4,398,352 A
- Document ID: US4398352A
- Status: Granted
- Kind: A
- Application number: 06/282,974
- Filed: 1981-07-13
- Granted: 1983-08-16
- Earliest claimed: 1981-07-13
- Assignees: Aviation Electric Ltd.
- Inventors: Arthur E. Maine
- Web page: https://patentgrep.com/patent/US4398352A

## CPC

- G01C 17/38: Testing, calibrating, or compensating of compasses
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)

## Abstract

A magnetic sensor is disclosed which features an arrangement that relies upon the principle of a fixed, non-pendulous magnetic sensing device (2), which is rendered insensitive to the effect of the earth's vertical magnetic field component by means of an adjacent cooperating magnetic member (20) pendulously-supported to maintain its axis along the true vertical. Means (34, 44, 46, 48, 50) are disclosed whereby the magnetic field provided by the pendulously-supported magnetic member is automatically adjusted to cancel the earth's vertical field even when the latter changes for any reason.

## Claims

### Claim 1

Apparatus for sensing the direction of the horizontal component of the earth's magnetic field to implement navigating a vehicle along a desired course, comprising:
a magnetic sensor strapped down to the vehicle structure so that the sensor axes and the vehicle axes coincide, whereby magnetism induced from the vehicle axes to the sensor axes when the vehicle pitches and rolls is essentially eliminated; and
a symmetrical coil member surrounding the strapped down sensor and pendulously-supported relative thereto, and energized fan generating a magnetic field which opposes the earth's vertical field to essentially eliminate the effect of said field on the sensor when the vehicle is displaced about at least one of its pitch and roll axes.

### Claim 2 (depends on 1)

Apparatus as described by claim 1, wherein:
the symmetrical coil member surrounding the strapped down sensor is pendulously-supported so as to be displaceable about the pitch, roll and yaw axes of the vehicle.

### Claim 3 (depends on 2)

Apparatus as described in claim 2, including:
means for restricting displacement of the pendulously-supported symmetrical coil member about the yaw axis of the vehicle.

### Claim 4 (depends on 1)

Apparatus as described by claim 1, including: a second magnetic sensor mounted on the pendulously-supported symmetrical coil member, with the axis of said second magnetic sensor being coincident with the axis of the pendulously-supported coil member; and
the pendulously-supported coil member coacting with the second sensor so that said sensor is responsive to the algebraic sum of the earth's vertical magnetic field and the magnetic field generated by the pendulously-supported member.

### Claim 5 (depends on 4)

Apparatus as described by claim 4, including:
means associated with the second sensor and the pendulously-supported coil member for affecting the magnetic field generated by the member, whereby the second sensor senses a zero magnetic field which occurs only when the magnetic field generated by said coil member cancels out the earth's vertical field.

### Claim 6 (depends on 5)

Apparatus as described by claim 5, wherein the means associated with the second sensor and the pendulously-supported coil member includes:
means for rigidly mounting the second sensor to the pendulously-supported coil member, with the second sensor providing an AC pulse output corresponding to the magnetic field sensed thereby;
means for demodulating the pulse output;
means for filtering the demodulated output to provide a DC output;
means for amplifying the DC output to provide a control output having a magnitude and sense commensurate with the magnetic field sensed by the second sensor; and
the control output being applied to the pendullously-supported coil member in a sense as to reduce the output from the second sensor rigidly mounted to the pendulously-supported coil member, thereby effectively cancelling the earth's vertical magnetic field by the field generated by the pendulously-supported coil member.

### Claim 7 (depends on 6)

Apparatus as described by claim 6, including:
a control circuit connected to the second sensor for providing anf output which affects the magnetic field generated by said sensor for cancelling out the vehicle's vertical field.

### Claim 8 (depends on 7)

Apparatus as described by claim 7, wherein the control circuit includes:
a resistor;
a positive voltage source connected to one leg of the resistor;
a negative voltage source connected to the other leg of the resistor;
a displaceable arm in cooperative relation with the resistor and displaced relative thereto to provide a correction signal commensurate with the vehicle's vertical field; and
the second sensor connected to the displaceable arm and responsive to the correction signal provided thereby for cancelling out the vehicle's vertical field.

### Claim 9

Apparatus for sensing the direction of the horizontal component of the earth's magnetic field to implement navigating a vehicle along a desired course, comprising:
a baseplate secured to a normally horizontal surface of the vehicle;
a pedestal mounted to the baseplate;
a torroidal magnetic sensor mounted to the pedestal and having a centrally disposed hole extending therethrough;
a post mounted to the pedestal and passing through the centrally disposed hole and drawn to a point on its end opposite the mounted end;
a hollow cylindrical core having a closed end and carrying a winding of insulated wire to provide a coil which surrounds the magnetic sensor, and carrying a detent on the inside of the closed end which pivotally engages the pointed end of the post;
a hollow cylindrical case having a closed end and mounted to the baseplate to surround the coil;
a screw axially aligned with the pose and in threaded engagement with the closed end of the case, and adjusted in the case to be just clear of a protrusion on the outside of the closed end of the core and axially aligned with the detent so that the coil is pendulously-supported between the pointed end of the post and the screw for displacement about pitch, roll and yaw axes of the vehicle;
the case being partially filled with a fluid to damp out extreme displacements about said axes; and
the coil being energized to generate a magnetic field which opposes the earth's vertical field to essentially eliminate the effect of said field on the sensor when the vehicle pitches and rolls, with the magnetic effects induced from the vehicle axes to the sensor axes when the vehicle pitches and rolls being essentially eliminated by virtue of the sensor being mounted to the vehicle surface.

### Claim 10 (depends on 9)

Apparatus as described by claim 9, including:
a hole in the closed end of the hollow cylindrical core;
a pin mounted in the closed end of the hollow cylindrical case; and
the pin engaging the hole in cooperative arrangement for limiting displacement of the coil about the vehicle yaw axis.

### Claim 11 (depends on 9)

Apparatus as described by claim 9, including:
a second magnetic sensor mounted on the protrusion on the outside closed end of the hollow cylindrical core so that its axis is coincident with the axis of the coil;
a hollow cylindrical carrier member surrounding the sensor, and having a closed end with a protrusion axially aligned with the protrusion on the outside of the closed end of the core;
the core having an open cylindrical portion extending above the closed end thereof and said insulated wire windings being carried on said portion so that the coil is extended to surround the first mentioned magnetic sensor and the second magnetic sensor;
the hollow cylindrical case surrounding the extended coil;
the screw axially aligned with the post and in threaded engagement with the closed end of the case being adjusted to be just clear of the protrusion on the closed end of the carrier member to maintain the alignment of the second sensor under conditions of vertical shock; and
the extended portion of the coil rendering the second sensor responsive to the algebraic sum of the earth's vertical magnetic field and the field produced by the pendulously-supported coil.