Patent ID: 6593745
Filing Date: 2003-07-15
Classification: E21B,G01C,G01V

Abstract:
In an overall system in which a boring tool is moved through the ground within a given region along a particular path while transmitting a locating signal which is to be detected by an antenna pair including first and second orthogonal antennas defining an antenna plane, the first and second antennas generating first and second signals, respectively, from the locating signal such that, for an initial fixed orientation of the antenna pair relative to the particular path in which the antenna plane extends generally along the particular path, the locating signal exhibits two different types of balance points for different above ground positions, at which balance points the first and second antennas each receive the locating signal having an equal magnitude such that the position of the antenna pair is ambiguous as to balance point type, an improvement for eliminating ambiguity as to the type of balance point, the improvement comprising the steps of:a) producing third and fourth signals in a predetermined way, which third and fourth signals may be obtained in one way by rotating the antenna pair by 45Â° from said initial fixed orientation in said antenna plane and measuring the locating signals with the rotated antenna pair; and b) determining at which type of said balance point the antenna pair is positioned based on said first, second, third and fourth signals.