Static magnetic field metal detector

Claim 2

Apparatus for detecting relative motion of a metal object comprising: means for generating a substantially uniform unidirectional magnetic field, multiple conductor magnetic field pick up coil means disposed in stationary relation in said unidirectional magnetic field and having output conductor means, said coil means having first and second sections symmetrically located about a mid-plane of said coil means, cross over conductor means for connecting opposite conductors of said first and second sections at said mid-plane for providing detection signal on said output conductor means in the presence of said object adjacent said first or said second sections while affording substantial cancellation of spurious magnetic field responses, threshold detector means coupled to said output conductor means, and utilization means responsive to said threshold means.

Claim 3

Apparatus as described in claim 1 additionally including band pass circuit means disposed in series relation between said output conductor means and said threshold detector means.

Claim 4

Apparatus as described in claim 1 wherein said magnetic field is provided by current flowing in elongate multiple conductor excitation coil means intimately associated with said pick up coil means.

Claim 5

Apparatus as described in claim 3 wherein substantial portions of said excitation and pick up coil means are interwoven on the same coil form.

Claim 6

Apparatus as described in claim 1 eherein said magnetic field is provided by permanent magnet means through which portions of said pick-up coil means are threaded in magnetic field coupled relation.

Claim 7

Apparatus as described in claim 2 additionally comprising attenuator means disposed in series circuit relation between said band pass filter means and said threshold detector means.

Claim 8

Apparatus as described in claim 1 wherein said threshold means comprises bipolar threshold detector means.

Claim 9

Apparatus for detecting relative motion of a metal object comprising: means for generating a substantially uniform unidirectional magnetic field, first and second multiple conductor magnetic field pick up coil means disposed in stationary relation in said unidirectional magnetic field and having respective first and second output conductor means, each of said coil means having first and second sections symmetrically located with respect to first and second mid-planes of said respective coil means, first cross over conductor means for connecting opposite conductors of said first and second sections of said first coil means at said first mid-plane for providing a first detection signal on said first output conductor means in the presence of said relatively moving object adjacent said first or second section of said first coil means, and second cross over conductor means for connecting opposite conductors of said first and second sections of said second coil means at said second mid-plane for providing a second detection signal on said second output conductor means in the presence of said relatively moving object adjacent said first or second section of said second coil means, said first and second coil means being off set longitudinally one relative to the other so that said first cross over lies proximate said first section of said second coil means and said second cross over meaNs lies proximate said second section of said first coil means for the purpose of providing output signals at said first or second output conductor means in the presence of said relatively moving object while affording substantial cancellation of spurious magnetic field responses.

Claim 10

Apparatus for detecting relative motion of a metal object comprising: means for generating a substantially uniform unidirectional magnetic field, first and second multiple conductor magnetic field pick up coil means disposed in stationary relation in said unidirectional magnetic field and having respective first and second output conductor means, each of said coil means having first and second sections symmetrically located with respect to first and second mid-planes of said respective coil means, first cross over conductor means for connecting opposite conductors of said first and second sections of said first coil means at said first mid-plane for providing a first detection signal on said first output conductor means in the presence of said relatively moving object adjacent said first or second section of said first coil means, and second cross over conductor means for connecting opposite conductors of said first and second sections of said second coil means at said second mid-plane for providing a second detection signal on said second output conductor means in the presence of said relatively moving object adjacent said first or second section of said second coil means, said first and second coil means being off set longitudinally one relative to the other so that said first cross over lies proximate said first section of said second coil means and said second cross over meaNs lies proximate said second section of said first coil means for the purpose of providing output signals at said first or second output conductor means in the presence of said relatively moving object while affording substantial cancellation of spurious magnetic field responses.

Claim 11

Apparatus as described in claim 8 additionally comprising: first and second signal processing circuit means respectively responsive to said first and second coil output conductor means, each said signal processing circuit means comprising in series circuit relation: band pass circuit means, and threshold detector means, OR circuit means responsive to said first and second signal processing means, and utilization means responsive to said OR circuit means.

Claim 12

Apparatus as described in claim 9 further comprising adjustable attenuator means interposed in series circuit relations between said band pass circuit means and said threshold detector means.

Claim 13

Apparatus as described in claim 10 further comprising full wave rectifier means interposed in series circuit relation between said band pass circuit means and said threshold detector means.

Claim 14

Apparatus as described in claim 9 wherein said utilization means comprises alarm means.

Claim 15

Apparatus as described in claim 9 wherein said utilization means comprises control means for operating controllable means.

Claim 16

Apparatus as described in claim 9 additionally comprising: a machine adapted for conveying bulk material along passage way means includng metallic materials whose presence it is desired to sense at a predetermined station, said machine having moving elements with a predetermined frequency spectrum of cyclic magnetic field variation, and means for supporting said pick up coil means and said field excitation means in close proximity to said passage way means in substantially symmetric relation with respect to said moving elements of said machine for the purpose of reducing response to spurious magnetic field variations, said band pass circuit means being adjusted to pass a spectrum of signals lying below said predetermined frequency spectrum for the further reduction of said response to spurious magnetic field variations.

Claim 17

Apparatus as described in claim 14 wherein said utilization means comprises means for stopping said machine.

Claim 18

Apparatus for detecting relative motion of a metal object comprising: means for generating a substantially uniform unidirectional magnetic field, multiple conductor magnetic field pick up coil means disposed in stationary relation in said unidirectional magnetic field and having output conductor means, said coil means having first and second sections symmetrically located about a mid-plane of said coil means, cross over conductor means for connecting opposite conductors of said first and second sections at said mid-plane for providing detection signals on said output conductor means in the presence of said object adjacent said first or said second sections while affording substantial cancellation of spurious magnetic field responses, band pass circuit means responsive to said detection signals on said output conductor means, full wave rectifier means responsive to said band pass circuit means, threshold detector means responsive to said full wave rectifier means, low pass amplifier means responsive to said rectifier means for generating a control voltage, means for supplying said control voltage to said threshold means for adjustably determining the threshold level of said threshold means, and utilization means responsive to said threshold means.

Claim 19

Apparatus for detecting relative motion of a metal object comprising: means for generating a substantially uniform unidirectional magnetic field, multiple conductor magnetic field pick up coil means disposed in stationary relation in said unidirectional magnetic field and having output conductor means, said coil means having first and second sections symmetrically located about a mid-plane of said coil means, cross over conductor means for connecting opposite conductors of said first and second sections at said mid-plane for providing detection signals on said output conductor means in the presence of said object adjacent said first or said second sections while affording substantial cancellation of spurious magnetic field responses, band pass circuit means responsive to said detection signals on said output conductor means, full wave rectifier means responsive to said band pass circuit means, threshold detector means responsive to said full wave rectifier means, low pass amplifier means responsive to said rectifier means for generating a control voltage, means for supplying said control voltage to said threshold means for adjustably determining the threshold level of said threshold means, and utilization means responsive to said threshold means.