Inductive sensor arrangement comprising three sense coils cooperating with said three field coils to form three field/sense coil pairs and method for detecting of ferrous metal objects

Abstract

An inductive sensor arrangement for detecting ferromagnetic or non-ferrous electrically conducting objects hidden in a surrounding medium comprising three field coils arranged in essentially the same geometric plane and adjacently positioned at angular distances of usually 120° from each other around a central axis orthogonal to the plane for generating an alternating magnetic flux by a sequential excitation with an AC-current ramp. The sensor arrangement further comprises three sense coils respectively mounted inside each associated field coil and in an orientation to the axes of each of the field coils such that essentially no voltage is induced in the sensor coils in an environment free of a metallic object. When a ferromagnetic or non-ferrous electrically conducting object approaches the sensor, nine characteristic voltage value sets are produced by the three sense coils which are stored and processed by an algorithmic process for defining a distinct criterion with respect to the position of the hidden metallic object to be located. The sensor arrangement uses a single point measurement to provide an accurate position and depth discrimination of the hidden ferromagnetic or non-ferrous electrically conducting object such as a rebar (R), a copper pipe in concrete or the like.