Apparatus and method for automatic product effect compensation in radio frequency metal detectors
First Claim
1. A metal detector adapted to transport a product through a region intersecting an electromagnetic field, comprising:
- (a) at least one coil residing within the electromagnetic field, the coil generating a signal in response to a disturbance of the electromagnetic field;
(b) an infeed sensor, the infeed sensor detecting entry of each product into the region intersecting the electromagnetic field and generating an infeed output signal in response thereto;
(c) an analog to digital converter, the analog to digital converter receiving the signal and generating a plurality of output signals, comprising;
i) a first output signal, the first output signal representing a reactive component of the signal generated by the coil; and
ii) a second output signal, the second output signal representing a resistive component of the signal generated by the coil;
(d) a reactive component learn memory, the reactive component learn memory receiving the first output signal and generating a reactive component reference signal in response thereto; and
(e) a reactive component synchronization processor, the reactive component synchronization processor receiving the infeed sensor output signal and the reactive component reference signal, the reactive component synchronization processor subtracting the reactive component reference signal from a reactive signal generated by a product being inspected by the metal detector so as to generate a subtracted reactive component signal having a substantially reduced product effect.
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Abstract
A metal detector used for identifying contaminants in packages on a conveyor. The detector includes coils a search head and an analog to digital converter generating a reactive signal and a resistive signal in response to the presence of a contaminant. During a learning mode a sample product passes through the metal detector providing a representative product effect signal which is stored by the reactive learn memory and the resistive learn memory. The learn memory values provide a reference value subtracted from each product signal during a normal production cycle, canceling the product effect caused by contaminants in individual packages. The product effect is monitored during successive cycles composed of a series of packages undergoing normal inspection by the metal detector. A tracking processor averages the product effect signal produced by the individual packages and continuously updates a product effect trend signal that is subtracted from each product signal.
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Citations
19 Claims
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1. A metal detector adapted to transport a product through a region intersecting an electromagnetic field, comprising:
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(a) at least one coil residing within the electromagnetic field, the coil generating a signal in response to a disturbance of the electromagnetic field; (b) an infeed sensor, the infeed sensor detecting entry of each product into the region intersecting the electromagnetic field and generating an infeed output signal in response thereto; (c) an analog to digital converter, the analog to digital converter receiving the signal and generating a plurality of output signals, comprising; i) a first output signal, the first output signal representing a reactive component of the signal generated by the coil; and ii) a second output signal, the second output signal representing a resistive component of the signal generated by the coil; (d) a reactive component learn memory, the reactive component learn memory receiving the first output signal and generating a reactive component reference signal in response thereto; and (e) a reactive component synchronization processor, the reactive component synchronization processor receiving the infeed sensor output signal and the reactive component reference signal, the reactive component synchronization processor subtracting the reactive component reference signal from a reactive signal generated by a product being inspected by the metal detector so as to generate a subtracted reactive component signal having a substantially reduced product effect. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A metal detector providing cancellation of a product effect, comprising:
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(a) transmitting and receiving coils capable of generating and detecting an electromagnetic field, respectively; (b) a search head housing the transmitting and receiving coils in a fixed configuration, the search head providing an analog resistive component signal and an analog reactive component signal; (c) an analog to digital converter interconnected to the search head for converting analog signals generated in response to a disturbance of the electromagnetic field into digital signals, the analog to digital converter providing a digital resistive component signal and a digital reactive component signal; (d) a means for transporting a product undergoing inspection through the electromagnetic field; (e) a high pass filter, the high pass filter being electrically interconnected to the analog to digital converter, the high pass filter passing a relatively narrower range of frequencies contained within the digital resistive component signal and a digital reactive component signal digital signals generated by the analog to digital converter to a tracking processor, wherein the tracking processor stores a number of digital resistive component signals and digital reactive component signals and generates an average value for the digital resistive component signal and the digital reactive component signal.
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17. A method of diminishing a product effect in a metal detector, comprising the steps of:
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(a) radiating an electromagnetic field into an aperture of the metal detector; (b) receiving the electromagnetic field, thereby producing a received signal; (c) introducing a representative sample product into the aperture while the electromagnetic field is present within the aperture; (d) separating the received signal into a resistive component and a reactive component; (e) calculating the average inherent product effect characteristics of products under test according to the formula
R=(P1+P2+ . . . +PN)/N, whereR is the average inherent product effect characteristic, P is a product effect of each individual package being inspected and N is the total number of packages inspected; (f) storing inherent product effect characteristics of the representative sample product, the inherent characteristics being constants; (g) subtracting the inherent product effect characteristics of the representative sample product from signals received by subsequent products undergoing inspection by the metal detector. - View Dependent Claims (18, 19)
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Specification