Patent ID: 7253628

Claim:
In a system in which a boring tool, including a drill string having a length which is fed out in a way which moves the boring tool through the ground in a region which includes at least one electrically conductive in-ground line, an apparatus for tracking a specific positional relationship between the boring tool and said line, said apparatus comprising: a transmitter for generating a magnetic field from one of either said boring tool or at least from an underground length of said line; a receiver carried by said boring tool if said magnetic field is generated from said line or in communication with said line if said magnetic field is generated from said boring tool for detecting a relative change in a particular characteristic of said magnetic field, which particular characteristic varies as a function of said specific positional relationship between said boring tool and said line as the boring tool moves through the ground within said region; a drill string monitor for monitoring a value of at least one parameter relating to the way in which said drill string is fed out; and a processor that is configured for correlating the detected relative changes in said characteristic with the value of said one parameter in a way which indicates certain changes in the positional relationship between said boring tool and said line which are indicative of the boring tool being on a collision course with the line without the need to establish an actual distance between the boring tool and said line.