US 3,971,983 AGranted

Ferromagnetic metal detector utilizing gradiometers positioned on opposite sides of the detection area with overlapping sensitivity

AssigneeInfinetics, Inc.

InventorJames R. Jaquet

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Abstract

A passive ferromagnetic detection station in which the position of the ferromagnetic object carried by a person may be indicated. A plurality of gradiometers mounted at predetermined vertical positions along two vertical members are used to sense any disturbances in the earth's magnetic field. Each gradiometer has a predetermined pattern or area of sensitivity to magnetic fields in which it senses disturbances in the earth's magnetic field. In a preferred embodiment the sensitivity patterns may overlap in predetermined areas. The outputs of the gradiometers are individually processed and converted to digital signals. The digital signals may be used to control a visual display device. In a preferred embodiment, the digital signals may be further processed through digital logic circuitry in order to reduce any false alarms by conditioning any output signal to the display device on the condition that all or a predetermined number of the gradiometers having an overlapping pattern in a particular area sense the ferromagnetic object.

Claims20

Dependent claims

Apparatus for detecting the presence of a ferromagnetic object passing through a station and indicating the location of said ferromagnetic object, comprising:

a first and a second member at said station, said first and second member having a plurality of gradiometers mounted thereon, each of said plurality of gradiometers having a predetermined pattern or area of sensitivity to magnetic fields which is substantially less than the total area between said first and second members, each of said plurality of gradiometers generating an output signal indicative of a change in the earth's magnetic field in response to the presence of a ferromagnetic object;
means for individually processing output signals generated by each of said plurality of gradiometers, said processing means being comprised of a plurality of processing channel means, each processing channel means receiving the output of at least one respective gradiometer and being operative to generate a digital signal in response to a predetermined change in the earth's magnetic field within the pattern or area of sensitivity to magnetic fields of said at least one respective gradiometer of said plurality of gradiometers;
and
means for indicating the position of said ferromagnetic object between said first and second members of said station, said indicating means including a plurality of indicators, each of said indicators being responsive to the digital signal generated in a respective one of said processing channel means.

1 more element

Apparatus for detecting the presence of a ferromagnetic object carried by a person and indicating the location of said ferromagnetic object, comprising:

a station having a first and second vertical members, said first and second vertical members having corresponding gradiometers at predetermined points along their lengths, each of said gradiometers having a predetermined pattern or area of sensitivity to magnetic fields, said patterns or areas of sensitivity to magnetic fields of said gradiometers having a predetermined amount of overlap, said overlap occurring in predetermined areas between said first and second vertical members, each gradiometer producing an output signal in response to a change in the earth's magnetic field generated in response to the presence of a ferromagnetic object within the gradiometer's pattern or area of sensitivity to magnetic fields;
first means for processing the output signal of each gradiometer, said processing means generating a digital signal for each gradiometer representative of a change in the earth's magnetic field within the pattern or area of sensitivity to magnetic fields of each gradiometer;
second means for processing output signals of said gradiometers, said second processing means receiving the output signals of the pairs of corresponding gradiometers on said first and second vertical members at a predetermined vertical position on said first and second vertical members, said second processing means forming a digital center signal indicating the presence of a ferromagnetic object within a predetermined distance of the center point between said first and second members;
digital logic means for producing output signals indicative of the position of the ferromagnetic object, said digital logic means receiving said digital signals from said first processing means and said center signals of said second processing means, said digital logic means producing a signal indicating the presence of a ferromagnetic object in a predetermined area only if a predetermined number of gradiometers having a sensitivity pattern in the predetermined area produce a signal indicating the presence of a ferromagnetic object;
and
means for indicating the position of said ferromagnetic object between said first and second vertical members, said indicating means being responsive to said outputs of said digital logic means.

3 more elements

Dependencies are inferred from the claim text.