Patent ID: 7029478

Claim:
A system for locating a target point for a drill bushing comprising: a probe having two drive coils, the drive coils being mounted in the probe and being oriented so that a magnetic field produced by the first drive coil in response to an alternating current being coupled to the first drive coil is orthogonal to a magnetic field produced by the second drive coil in response to an alternating current being coupled to the second drive coil; a guide having a pair of sensor planes mounted proximate a drill bushing, the sensor planes being orthogonal to one another, each sensor plane containing a pair of sensors, each sensor generating an electrical signal in response to magnetic fields produced by the first and the second drive coils; and a computer coupled to the sensors in each sensor plane to receive signal readings from each sensor and to determine the target point of the drill bushing to which the pair of sensor planes is mounted.