Patent ID: 7414400

Claim:
An apparatus for use in detecting a ferromagnetic object, the apparatus comprising: guide members defining a path along which persons, who are potentially transporting a ferromagnetic object, are prescribed to pass; said guide members being arranged such that said path is located, in use, in a magnetic field; a pair of sensing assemblies mounted at the guide members and arranged at a predetermined location and orientation relative to the guide members such that, as a person transporting a ferromagnetic object to be detected passes along the prescribed path, the movement of the ferromagnetic object in the magnetic field causes a voltage to be generated in the sensing assemblies; and an electrical measuring device for measuring an electrical signal generated by the sensing assemblies when the ferromagnetic object travels in the path, the electrical measuring device being arranged to provide a warning indication when the electrical signal exceeds a predetermined value; wherein the sensing assemblies each include a primary sensing device and at least one secondary sensing device spaced at a different distance relative to the primary sensing device from the path and arranged to reduce components of electrical signal generated by fields or movements outside of the path sufficiently to avoid false warning indications caused by said fields or movements.