US 2010/0148761 A1 · Speed filter calibration apparatus and method for radio frequency metal detectors

Abstract

A metal detector (40) used for identifying contaminants in products (23) introduced into the metal detector by a conveyor. The detector (40) includes coils (1), a search head (2) and an analog to digital converter (3) that generates a reactive signal (13) in response to the presence of a contaminant in the region of the coils. A calculation processor (32 ) receives the reactive signal (13) along with the value of the conveyor speed (9) to determine a calibration ratio R that is unique to each individual metal detector (40). The optimum frequency F for metal detector operation is equal to the conveyor speed (9) divided by the ratio R. The ratio R simplifies the selection of filter parameters (4, 8) for a speed filter (30) which correlates the conveyor speed (9) with the frequency F so as to deliver an optimized signal to the detection algorithm (10) used to determine the presence of a contaminant based on the signal (13) derived from the coils (1).

Claims20

Dependent claims

A metal detector, comprising:

(a) at least one coil residing within an electromagnetic field, the coil generating a signal in response to a disturbance of the electromagnetic field;
(b) a conveyor, the conveyor transporting a product through a region intersecting the electromagnetic field at a conveyor velocity;
(c) a filter, the filter being adapted to receive the signal and to alter a characteristic of the signal;
(d) a filter control, the filter control being interconnected to the filter, the filter control being adapted to modify a characteristic of the filter;
and
(e) a filter calibrator, the filter calibrator being adapted to determine an inherent parameter of the metal detector so as to permit the filter control to optimize operation of the filter by referring to a relationship between the conveyor velocity and the inherent parameter.

3 more elements

A metal detector providing substantially permanent speed filter calibration, comprising:

(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;
(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;
(d) a conveyor, the conveyor transporting a product undergoing inspection through the electromagnetic field at a velocity;
(e) a speed filter, the speed filter being electrically interconnected to the analog to digital converter, the speed filter passing a relatively narrow band of frequencies of digital signals generated by the analog to digital converter to a detection processor;
(f) a speed filter control, the speed filter control adjusting an optimal center frequency used by the speed filter to establish the relatively narrow band of frequencies passed by the speed filter;
and
(g) a calibration processor, the calibration processor generating a constant parameter uniquely associated with the metal detector, the constant parameter being forwarded to the speed filter control, the constant parameter being used by the speed filter control in substantially all subsequent calculations relating to a determination of the optimal center frequency used by the speed filter.

5 more elements

Dependencies are inferred from the claim text.

Speed filter calibration apparatus and method for radio frequency metal detectors

Life of this patent

Speed filter calibration apparatus and method for radio frequency metal detectors

Life of this patent

Abstract

Claims20