Method for locating an inaccessible object having a magnetic field generating solenoid
First Claim
1. A method of locating an inaccessible object, which object has a solenoid (10) for generating a magnetic field, the method comprising:
- a) storing information relating to the relationship between the ratio of the axial and radial components of the magnetic field at a plurality of points in the plane containing the axis of the solenoid (10) and the angle between the axis of the solenoid (10) and the line joining each of the plurality of points to the center of the solenoid (10);
b) determining the ratio of the axial and radial components of the magnetic field at a measurement location; and
c) determining the one of the plurality of points which corresponds to the measurement location, on the basis of said information and said ratio of the axial and radial components thereby to determine the location of the object relative to the measurement location.
1 Assignment
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Accused Products
Abstract
In order to locate an inaccessible object, such as an underground boring tool (30), a solenoid (10) on or in the tool generates a magnetic field which is detected at two measuring locations (20, 21). Information relating to the relationship between the axial and radial components of the field from the solenoid (10) are stored, and comparison of the measured values of the axial and radial components at the measurement locations (20, 21) enables the direction of the solenoid (10) from the measurement locations (20, 21) to be determined. The known attenuation of the magnetic field from the solenoid (10) enables the distance between the solenoid (10) and the measurement locations to be determined from the absolute value of the field at the measurement locations (20, 21) and the direction to the solenoid (10). The present invention thus makes use of the fact that there is a known relationship between the axial and radial fields of the solenoid (10) at any point in the plane containing the solenoid and the line joining the measurement location to the solenoid. A tilt sensor may be provided to indicate if the axis of the solenoid is not horizontal, to enable axial radial directions to be determined.
147 Citations
12 Claims
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1. A method of locating an inaccessible object, which object has a solenoid (10) for generating a magnetic field, the method comprising:
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a) storing information relating to the relationship between the ratio of the axial and radial components of the magnetic field at a plurality of points in the plane containing the axis of the solenoid (10) and the angle between the axis of the solenoid (10) and the line joining each of the plurality of points to the center of the solenoid (10); b) determining the ratio of the axial and radial components of the magnetic field at a measurement location; and c) determining the one of the plurality of points which corresponds to the measurement location, on the basis of said information and said ratio of the axial and radial components thereby to determine the location of the object relative to the measurement location.
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2. A method according to claim 1, wherein the object has a tilt sensor (32) for determining the orientation of the solenoid (10), thereby to determine the direction of the axial and radial components at the measurement location.
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3. A method according to claim 1, wherein the horizontal and vertical components of the magnetic field are measured at the measurement location, and the axial and radial components derived from the horizontal and vertical components.
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4. A method according to claim 1, wherein the absolute value of the magnetic field at the measurement location is determined.
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5. A method according to claim 4, further including determining the distance between the measuring point and the solenoid (10) using the absolute value of the magnetic field and a known attenuation value for the magnetic field.
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6. A method according to claim 1, further including determining the component of the magnetic field at the measuring location in a direction perpendicular to the vertical plane containing the line joining the solenoid (10) and the measurement location.
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7. A method of locating an inaccessible object, which object has a solenoid (10) for generating a magnetic field, the method comprising:
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a) storing information relating to the relationship between the ratio of the axial and radial components of the magnetic field at a plurality of points in the plane containing the axis of the solenoid (10) and the angle between the axis of the solenoid (10) and the line joining each of the plurality of points to the center of the solenoid; b) determining the ratio of the axial and radial components of the magnetic field at a plurality of measurement locations, c) determining each one of the plurality of points which corresponds to said plurality of measurement locations, thereby to determine the location of the object relative to each of the measurement locations; and d) comparing the spatial relationship between each of the plurality of points with the spatial relationship between each of said plurality of measurement points.
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8. A method according to claim 7, wherein the object has a tilt sensor (32) for determining the orientation of the solenoid, thereby to determine the direction of the axial and radial components at the measurement location.
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9. A method according to claim 7, wherein the horizontal and vertical components of the magnetic field are measured at the measurement locations, and the axial and radial components derived from the horizontal and vertical components.
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10. A method according to claim 7, wherein the absolute value of the magnetic field at each measurement location is determined.
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11. A method according to claim 10, further including determining the distances between each measuring point and the solenoid using the absolute value of the magnetic field at each measuring point and a known attenuation value for the magnetic field.
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12. A method according to claim 7, further including determining the component of the magnetic field at each measurement location in a direction perpendicular to the vertical plane containing the line joining the solenoid and each measurement location.
Specification