Methods and apparatus according to the invention include inductive units or apparatus such as magnetic metal detectors comprising multiple electromagnetic coils and circuit boards such as electronic printed circuit boards (PCBs) so that the circuit boards, while containing metallic surfaces and layers, are positioned in such a way as to reduce or eliminate their effect on the metal detector's coils. The apparatus comprising: a plurality of electromagnetic coils and a plurality of circuit boards, and wherein at least one of said circuit boards is positioned so that its thickness direction is orthogonal to the magnetic field of at least one of said coils.

The invention relates to a ground sensor (1) for detecting the quality of a substratum, comprising at least one electromagnetic transmission coil (2) and at least one pair of electromagnetic receiving coils (3, 3), wherein the transmission coil (2) is designed to generate an electromagnetic primary field, and the receiving coils (3, 3) are designed to receive an electromagnetic secondary field induced in the substratum by the primary field. The ground sensor (1) has a central plane E, the transmission coil (2) is arranged in the region of the central plane E, and the receiving coils (3, 3) are arranged at a distance d.sub.1 which is equidistant to the central plane E.

A metal sensor, a method for analyzing a measurement signal of the sensor, and a method for detecting an object surrounded by a medium via the sensor. The metal sensor has at least one transmission coil and at least one receiving coil system inductively coupled to each other, wherein the receiving coil system comprises at least one first receiving coil and at least one second receiving coil located in a same plane; the transmission coil forms a projection on the plane; an area formed by the first receiving coil on the plane contains the projection; and an area formed by the second receiving coil on the plane is arranged around the projection. The receiving coils are arranged to have a same winding direction, produce induction with a second magnetic field generated by a target metal object, and generate induced voltages superimposed on one another other on the receiving coils.

A metal detector has a large primary transmit coil, a small primary feedback bucking coil, a first receive coil, and a second receive coil. A variable resistance device is connected to the first and second receive coils. A voltage source is connected to the large primary transmit coil. The voltage source is oppositely connected to the small primary feedback bucking coil. A primary voltage is provided to the large primary transmit coil. A reverse primary voltage is provided to the small primary feedback bucking coil. The small primary feedback bucking coil is positioned near the first and the second receive coils. The metal detection methods and apparatus sums up the signals from the two secondary coils. One is over nulled, the other is under nulled. They are close enough to an inductive null to attenuate the stray coupled signals from the primary driving signal and detecting the object.

A metal detection apparatus (9) is tested with a test device (7) having at least one test article (79), movable through a detection zone (60). The test article is moved through the detection zone along a first transfer axis (ca) and a first input signal is measured. A first threshold (th1) is determined, where an amplitude of the first input signal exceeds the first threshold (th1). Then, an identical test article is moved through the detection zone along a further transfer axis (ta; . . . ) and a further input signal is measured and a further threshold (th2; . . . ) is determined, where an amplitude of the further input signal exceeds the further threshold (th2; . . . ). The first or further threshold (th1; th2; . . . ) is selected in the signal processing path (4) whenever the test article is moved along the related transfer axis (ca; ta; . . . ).

Man-portable locator systems for locating buried or otherwise inaccessible pipes, conduits, cables, wires and inserted transmitters using detector arrays and stochastic signal processing and similar techniques to analyze and display multiple target objects at differing frequencies in a layered user interface (UI) are disclosed.

Man-portable locator systems for locating buried or otherwise inaccessible pipes, conduits, cables, wires and inserted transmitters using detector arrays and stochastic signal processing and similar techniques to analyze and display multiple target objects at differing frequencies in a layered user interface (UI) are disclosed.

A magnetic flux measurement apparatus and method for nondestructive thickness imaging of metallic objects. The apparatus can primarily be used for thickness imaging of concentric metallic pipes, such as inner tubing and outer casing pipes in downhole applications. The magnetic flux measurement apparatus includes a transducer that includes a magnetic field source, magnetic flux sensor rings and a magnetic flux guide lens both positioned in alignment with a lateral axis of the magnetic field source. The magnetic flux guide lens is made of ferromagnetic material with high magnetic permeability that can direct flux lines into a predetermined sensor area for higher sensitivity and signal to noise ratio.

An apparatus (1) for detecting metal is equipped with at least one test device (2) with a non-metallic guide tube (21). Only a proximal end of the guide tube is connected to a pneumatic control unit (3). A distal end of the guide tube has at least one first ventilation port (211). A test article (7), having a known mass of metal, is movable back and forth between the proximal end and the distal end of the guide tube, at least through a section of an electromagnetic field, to verify operation of the metal detection The pneumatic control unit can use air pressure, either elevated above or reduced below the ambient pressure, applied to the proximal end of the guide tube in order to drive the test article back and forth, or only in one direction if it is returned by gravitational force.

Methods and apparatus according to the invention include inductive units or apparatus such as magnetic metal detectors comprising multiple electromagnetic coils and circuit boards such as electronic printed circuit boards (PCBs) so that the circuit boards, while containing metallic surfaces and layers, are positioned in such a way as to reduce or eliminate their effect on the metal detector's coils. The apparatus comprising: a plurality of electromagnetic coils and a plurality of circuit boards, and wherein at least one of said circuit boards is positioned so that its thickness direction is orthogonal to the magnetic field of at least one of said coils.