Device for detecting metallic objects in a flow of non-metallic material
First Claim
1. A device for detecting the presence of metallic objects in a flow of non-metallic material, comprising:
- a scanning coil located in said flow and including a primary coil and a secondary coil;
at least first and second current sources for providing at least first and second alternating currents at different frequencies to said primary coil;
an output circuit responsive to the output signals of said secondary coil and providing an output when a metal object is sensed by said scanning coil;
said output circuit including at least first and second means for respectively rectifying said output signals of said secondary coil corresponding to each of said first and second alternating currents and being respectively controlled by said first and second alternating current sources with a given phase angle relative to the respective alternating current thereof;
at least first and second means for multiplying the respective outputs of said first and second rectifier means by respective first and second factors, with at least one of said first and second factors including a term representative of the relationship between the respective frequencies of said first and second alternating currents; and
means for deriving an output signal from the difference between the respective outputs of said first and second means for multiplying, said output signal being representative of the presence of metallic objects in said flow of non-metallic material.
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Accused Products
Abstract
A device for detecting metallic objects in a material flow, comprising as sensing member a scanning coil consisting of a primary coil and, for example, two oppositely connected secondary windings arranged symmetrically around the primary winding so that the voltage induced in the secondary winding becomes zero as long as no conducting objects appear in the scanning area. To eliminate irrelevant signals from conducting objects in the vicinity of the scanning coil but not in the material flow or from weakly conducting objects in the material flow, the primary winding is fed with at least two alternating currents having different frequencies. The corresponding secondary voltages are rectified in phase-controlled rectifiers, and in a calculating circuit the difference is derived between the output of one rectifier voltage and the output of another rectifier multiplied by a constant factor which includes the relation between the frequencies of the corresponding alternating voltages.
72 Citations
13 Claims
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1. A device for detecting the presence of metallic objects in a flow of non-metallic material, comprising:
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a scanning coil located in said flow and including a primary coil and a secondary coil; at least first and second current sources for providing at least first and second alternating currents at different frequencies to said primary coil; an output circuit responsive to the output signals of said secondary coil and providing an output when a metal object is sensed by said scanning coil; said output circuit including at least first and second means for respectively rectifying said output signals of said secondary coil corresponding to each of said first and second alternating currents and being respectively controlled by said first and second alternating current sources with a given phase angle relative to the respective alternating current thereof; at least first and second means for multiplying the respective outputs of said first and second rectifier means by respective first and second factors, with at least one of said first and second factors including a term representative of the relationship between the respective frequencies of said first and second alternating currents; and means for deriving an output signal from the difference between the respective outputs of said first and second means for multiplying, said output signal being representative of the presence of metallic objects in said flow of non-metallic material. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13)
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11. k is a constant close to zero.
Specification