Method and apparatus to minimize gradient errors in buried utility depth measurements

摘要

A buried utility locator uses the “gradient method” to determine the depth of a buried, current-carrying utility. The method and corresponding apparatus used in said locator, to minimize field gradient measurement errors, includes first and second antennas. Both the first and second antennas are mounted along a common vertical axis inside the locator's housing. The first antenna is a gradiometer formed by two vertically spaced-apart magnetic field sensors connected in a differential configuration. The second antenna provides a secondary field measurement along the direction of the gradient sensor axes.

主权项

1. 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.