Hilti Aktiengesellschaft

Roger Golder

Albert Binder

Philip Jones

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&deg; 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.

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

The inductive sensor arrangement for detecting metal objects hidden in a surrounding medium comprises a pair of field coils for generating an alternating magnetic flux by a sequential excitation with an AC-current and a pair of sense coils respectively mounted inside each associated field coil in an orientation to the axes of each of said field coils such that essentially no voltage is induced in said sensor coils in an environment free of a metallic object. If a metallic object comes into the vicinity of the inductive sensor four characteristic voltage value sets are produced by the sense coil pair which become subject of an algorithmic processing for defining a position and distinction criterion in respect to said hidden metallic object. The sensor arrangement has the advantage of a single point measurement resulting in an accurate position discrimination for a hidden metallic object like a rebar in concrete.

Inductive sensor arrangement with field coils and sense coils, and methods for detecting ferrous objects

An inductive sensor head for detecting ferrous or non-ferrous electrically conducting objects, in particular rebars in a surrounding medium like concrete or a brick wall, comprising at least one field coil with a small axial length compared to its diameter and at least one twin pair of sense coils with a small diameter compared to the diameter of the field coil. The number of turns of wire on the field coil is small relative to the number of turns of wire on the sense coils. The common axis of the sense coils is arranged perpendicular to the axis of the field coil so that there will be no component or a minimum component of maximum flux that is coaxial with the sense coils. A twin pair of coaxially arranged identical field coils is provided that are sequentially excited for giving not only positional but also depths information. In a center plane between the field coils an orthogonal arrangement of two twin pairs of sense coils is provided enabling for a three-dimensional hidden object positioning. The sensor head according to the invention can be automatically calibrated, controlled and read out under control of a microcontroller.

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Cambridge, United Kingdom

Roger Golder