Walk-over Locating Technology

This paper describes the walk-over locating technology used in horizontal directional drilling. It covers both the fundamentals of the technology and practical applications. The paper begins with a comparison of the two types of magnetic fields used for in-ground locating. The cylindrical magnetic field is used for locating wires, pipes, and conduits, while the dipole magnetic field is used to track drill heads. Plots show the magnitude of the signal intensity as detected by various receiver antenna configurations for the two types of fields. The paper then goes on to show the flux patterns on the surface of the ground and their importance to locating. A description is given of the various ways that different dipole tracking receivers can process the magnetic field information to locate the in-ground magnetic field source and determine its depth and orientation. The methods described include the use of magnetic field intensity, flux line orientation, and gradients of the field intensity. The ability to predict the location and depth of the boring tool at a point in front of its current position is discussed, including how this feature can be used to guide the drilling process. Finally, the paper describes a novel device that can represent the tracking transmitter’s position on a display much like a radar screen so that the position of the transmitter relative to the receiver can be displayed regardless of the orientation of either device. This device uses both the magnetic flux lines and the intensity of the field for locating the transmitter, and its design appears to be the next major advancement in walk-over locating technology