Patent ID: 8878537

Claim:
A locator that uses a direct magnetic field gradient signal and corresponding secondary signal provided by an apparatus to determine the depth of a buried field-emitting utility or subsurface generator, the locator apparatus comprising: a first antenna including first and second magnetic field sensors mounted at fixed, spaced apart locations along a vertical axis of the locator, the first and second sensors being configured to provide a direct magnetic field gradient signal indicating a difference of the magnetic fields between first and second sensing locations occupied by the first and second sensors, respectively, along the vertical axis; a second antenna having a third magnetic field sensor mounted at a fixed location along the vertical axis of the locator to sense the magnetic field along an axis parallel to the axes of the gradient sensors; the third sensor providing a secondary output signal indicating the magnetic field detected at a sensing location of the third sensor; and circuitry coupled to the first and second antennas, the circuitry conditioning, processing, converting signals from the antennas and calculating a depth of the utility based on a minimal error, direct magnetic field gradient signal received from the first antenna and from the secondary output signal received from the second antenna.