Static magnetic field metal detector

Claim 2

In a crop harvester having rotatable machine elements including crop processing elements susceptible to damage by a tramp metal part moving through a crop input region toward said crop processing elements, the combination comprising: first and second elongate magnetic field generation means for producing respective first and second unidirectional magnetic fields in discrete portions of said crop input region, said first magnetic field being opposite in sense to said second magnetic field and of substantially equal strength, multiple conductor magnetic field pick-up coil means disposed substantially equally in stationary relation in said first and second unidirectional magnetic fields for providing a detection signal in the presence of said object adjacent said first or said second elongate magnetic field generation means while affording substantial cancellation of spurious magnetic field responses, and utilization means coupled to said multiple conductor magnetic field pick-up coil means.

Claim 3

Apparatus as described in claim 1 wherein: said harvester has a substantial degree of symmetry about a vertical plane, and said first and second magnetic field generation means are disposed substantially symmetrically on either side of said vertical plane in relation to said rotatable machine elements to provide substantial cancellation of spurious varying magnetic fields generated by said rotatable machine elements.

Claim 4

Apparatus as described in claim 2 additionally including in series relation between said multiple conductor pick-up coil means and said utilization means: band pass circuit means, full wave rectifier means responsive to said band pass circuit means, trigger pulse generator means responsive to said full wave rectifier means, and switching circuit means for supplying power to said utilization means.

Claim 5

Apparatus as described in claim 1 wherein said utilization means comprises control means for stopping said rotatable machine elements subject to damage by said tramp metal parts.

Claim 6

Apparatus as described in claim 1 wherein said utilization means comprises control means for operating controllable means.

Claim 7

Apparatus as described in claim 1 wherein said rotatable machine elements comprise moving elements with a predetermined spectrum of cyclic magnetic field variations, said combination further including: means for supporting said magnetic field pick-up coil means and said first and second elongate magnetic field generation means in close proximity to passage way means in substantially symmetric relation with respect to said rotatable machine elements for the purpose of reducing response to spurious magnetic field variations, and bandpass circuit means 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 8

Apparatus for detecting relative motion of a metal object through a region of space comprising: first and second elongate magnetic field generation means for producing respective first and second unidirectional magnetic fields in discrete portions of said region of space, said first magnetic field being opposite in sense to said second magnetic field and of substantially equal strength, said first elongate magnetic field generation means comprises first elongate permanent magnet means having first and second elongate substantially parallel-disposed magnetic poles at one face thereof, said second elongate magnetic field generation means comprises second elongate permanent magnet means having third and fourth substantially parallel-disposed magnetic poles at one face thereof, said first, second, third, and fourth poles being characterized by production of an extended magnetic field of one sense adjacent said one face of said first elongate permanent magnet means and an extended magnetic field of opposite sense adjacent sAid one face of said second elongate permanent magnet means, multiple conductor magnetic field pick-up coil mens disposed substantially equally in stationary relation in said first and second unidirectional magnetic fields for providing a detection signal in the presence of said object adjacent said first or said second elongate magnetic field generation means while affording substantial cancellation of spurious magnetic field responses, utilization means for operating controllable means coupled to said multiple conductor magnetic field pick-up coil means, and signal processor means disposed in series relation between said multiple conductor pick-up coil means and said utilization means comprising: band pass circuit means, full wave rectifier means responsive to said band pass circuit means, trigger pulse generator means responsive to said full wave rectifier means, and switching circuit means for supplying power to said utilization means.

Claim 9

Apparatus for detecting relative motion of a metal object through a region of space comprising: first and second elongate magnetic field generation means for producing respective first and second unidirectional magnetic fields in discrete portions of said region of space, said first magnetic field being opposite in sense to said second magnetic field and of substantially equal strength, said first elongate magnetic field generation means comprises first elongate permanent magnet means having first and second elongate substantially parallel-disposed magnetic poles at one face thereof, said second elongate magnetic field generation means comprises second elongate permanent magnet means having third and fourth substantially parallel-disposed magnetic poles at one face thereof, said first, second, third, and fourth poles being characterized by production of an extended magnetic field of one sense adjacent said one face of said first elongate permanent magnet means and an extended magnetic field of opposite sense adjacent sAid one face of said second elongate permanent magnet means, multiple conductor magnetic field pick-up coil mens disposed substantially equally in stationary relation in said first and second unidirectional magnetic fields for providing a detection signal in the presence of said object adjacent said first or said second elongate magnetic field generation means while affording substantial cancellation of spurious magnetic field responses, utilization means for operating controllable means coupled to said multiple conductor magnetic field pick-up coil means, and signal processor means disposed in series relation between said multiple conductor pick-up coil means and said utilization means comprising: band pass circuit means, full wave rectifier means responsive to said band pass circuit means, trigger pulse generator means responsive to said full wave rectifier means, and switching circuit means for supplying power to said utilization means.

Claim 10

Apparatus for detecting relative motion of a metal object through a region of space comprising: first and second elongate magnetic field generation means for producing respective first and second unidirectional magnetic fields in discrete portions of said region of space, said first magnetic field being opposite in sense to said second magnetic field and of substantially equal strength, multiple conductor magnetic field pick-up coil means disposed substantially equally in stationary relation in said first and second unidirectional magnetic fields for providing a detection signal in the presence of said object adjacent said first or said second elongate magnetic field generation means while affording substantial cancellation of spurious magnetic field responses, utilization means coupled to said multiple conductor magnetic field pick up coil means, band pass circuit means disposed in series relation between said multiple conductor pick-up coil means and said utilization means, a machine adapted for conveying bulk material along passage way means including 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 first and second magnetic field generation 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 11

Apparatus for detecting relative motion of a metal object through a region of space comprising: first and second elongate magnetic field generation means for producing respective first and second unidirectional magnetic fields in discrete portions of said region of space, said first magnetic field being opposite in sense to said second magnetic field and of substantially equal strength, multiple conductor magnetic field pick-up coil means disposed substantially equally in stationary relation in said first and second unidirectional magnetic fields for providing a detection signal in the presence of said object adjacent said first or said second elongate magnetic field generation means while affording substantial cancellation of spurious magnetic field responses, utilization means coupled to said multiple conductor magnetic field pick up coil means, band pass circuit means disposed in series relation between said multiple conductor pick-up coil means and said utilization means, a machine adapted for conveying bulk material along passage way means including 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 first and second magnetic field generation 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.