Patent ID: 6362739
Filing Date: 2002-03-26
Classification: G08B

Abstract:
A device for detecting the presence of a ferromagnetic object, the device comprising:at least one coil formed from a multiple winding of a wire; a controller comprising an alarm; a non-magnetic, conductive shield enclosing the at least one coil so as to shield said coil from high frequencies while allowing very low frequencies associated with ferromagnetic weapons moving relative to the device to pass through the shield; and wherein said at least one coil is constructed and arranged such that, upon the relative motion of the ferromagnetic object proximate said at least one coil, a voltage induced in the coil is transmitted to said controller; and wherein the at least one coil is wound onto a magnetically permeable core; wherein said at least one coil includes a first coil and a second coil, said first and second coils being wound differentially such that the ferromagnetic object is detected only when the object is closer to one of said coils than the other of said coils; and wherein said controller is constructed and arranged to determine whether said induced voltage falls within a predetermine range and, if so, to trigger said alarm.