Speed-independent static magnetic field metal detector
AssigneeSperry Rand Corporation
InventorsClarence L. Bennett, Jr., Carl E. Bohman
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Abstract
A static magnetic field detector for harvesting machines senses the passage of ferrous or magnetic objects utilizing a balanced magnetic field excitation configuration which provides substantial self-cancellation of spurious background signals. A novel filtering means provides normalization of the fluctuations in the background noise due to the variations in the angular velocity of the rotating harvesting machine components. Additionally, the detector apparatus is disposed within a compressor feed roll of the machine thereby reducing the area which must be scanned and increasing the sensitivity of the device.
Claims10
In a static magnetic field detector for protecting rotatable machine elements in a harvesting machine that are susceptible to damage by tramp metal, said detector having means for generating a magnetic field and at least one magnetic pickup coil means, apparatus comprising:
- lowpass filter means coupled to the output of said pickup coil means and having an attenuation characteristic with a slope substantially equal and opposite to the slope characteristic of the fluctuations in the output signal from the pickup coil means due to variations in the angular velocities of the rotatable machine elements, such that the amplitude of the output signal from said lowpass filter means is maintained substantially constant with respect to said fluctuations in the angular velocities of said rotatable machine elements;
- bandpass circuit means coupled to said filter means and adjusted to pass the range of signals within a predetermined frequency spectrum for attenuating the response of said pickup coil means to spurious magnetic field variations due to said rotating machine elements and other sources without said predetermined frequency spectrum;
- and
- utilization means, coupled to said bandpass circuit means, and responsive to signals indicative of the presence of tramp metal, for stopping the operation of said machine and alerting the operator thereto.
Dependencies are inferred from the claim text.