| 摘要 |
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.
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