Metal detector
First Claim
1. A metal detector for detecting the presence of foreign ferromagnetic or electrically conductive articles in an object to be investigated, which compensates for the bulk effect which results from the size or shape of the object, comprising:
- an electromagnetic radiator formed as a loop antenna;
an oscillator circuit having an output frequency which is dependent upon the inductive load presented by the electromagnetic radiator, the oscillator circuit being arranged to supply a first, ac electrical signal to the electromagnetic radiator such that the electromagnetic radiator generates an alternating magnetic field;
first and second electromagnetic receiving antennae electrically connected to one another and each being arranged in proximity to the electromagnetic radiator such that lines of flux of the alternating magnetic field link the first and second receiving antennae;
a receiving antenna signal detector electrically connected with the first and second electromagnetic receiving antennae and arranged to provide an output indicative of the amplitude of a second electrical signal induced in the first and second antennae;
an oscillator circuit signal detector electrically connected with the oscillator circuit and arranged to provide an output representative of a parameter of the first ac electrical signal supplied thereby, wherein said parameter varies with the proximity of said object and said electromagnetic radiator; and
processor means in communication with the receiving antenna signal detector and the oscillator circuit signal detector, the processor means being arranged to monitor the output of the oscillator circuit signal detector and to adjust the output of the receiving antenna signal detector in dependence upon the output of the oscillator circuit signal detector, in order to compensate for changes in the parameter of the first ac electrical signal caused by the presence in the proximity of the electromagnetic radiator of the object to be investigated.
1 Assignment
0 Petitions
Accused Products
Abstract
A metal detector has a circular excitation coil (10) through which foodstuffs to be tested (65) pass, on a conveyor belt (40). The excitation coil (10) is excited by a stable oscillator (50) and the lines of flux generated by the excitation coil (10) link two receiver coils (20, 30) equidistantly spaced either side of the excitation coil (10). As a foodstuff (65) having a foreign ferromagnetic or electrically conductive object therein passes through the receiver coils (20, 30), a voltage is induced in them. This induced voltage is phase compensated. The change in amplitude or frequency of the oscillator (50) as the foodstuff (65) moves through the excitation coil (10) is also passed to the processor (70) which removes the artifacts from the detector signal caused by the volume of the foodstuff (65) itself. The resultant signal, which was previously swamped by the effect of the volume of the foodstuff itself, can then be detected and the foodstuff can be removed from the conveyor (40).
-
Citations
14 Claims
-
1. A metal detector for detecting the presence of foreign ferromagnetic or electrically conductive articles in an object to be investigated, which compensates for the bulk effect which results from the size or shape of the object, comprising:
-
an electromagnetic radiator formed as a loop antenna; an oscillator circuit having an output frequency which is dependent upon the inductive load presented by the electromagnetic radiator, the oscillator circuit being arranged to supply a first, ac electrical signal to the electromagnetic radiator such that the electromagnetic radiator generates an alternating magnetic field; first and second electromagnetic receiving antennae electrically connected to one another and each being arranged in proximity to the electromagnetic radiator such that lines of flux of the alternating magnetic field link the first and second receiving antennae; a receiving antenna signal detector electrically connected with the first and second electromagnetic receiving antennae and arranged to provide an output indicative of the amplitude of a second electrical signal induced in the first and second antennae; an oscillator circuit signal detector electrically connected with the oscillator circuit and arranged to provide an output representative of a parameter of the first ac electrical signal supplied thereby, wherein said parameter varies with the proximity of said object and said electromagnetic radiator; and processor means in communication with the receiving antenna signal detector and the oscillator circuit signal detector, the processor means being arranged to monitor the output of the oscillator circuit signal detector and to adjust the output of the receiving antenna signal detector in dependence upon the output of the oscillator circuit signal detector, in order to compensate for changes in the parameter of the first ac electrical signal caused by the presence in the proximity of the electromagnetic radiator of the object to be investigated. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 13)
-
-
9. A method for detecting the presence of foreign ferromagnetic or electrically conductive articles in an object to be investigated, and compensating for the bulk effect which results from the size or shape of the object, the method comprising the steps of:
-
supplying a first ac electrical signal from an oscillator circuit to an electromagnetic radiator formed as a loop antenna such that an alternating magnetic field is generated thereby, the oscillator circuit having an output frequency which is dependent upon the inductive load presented by the electromagnetic radiator; providing first and second electromagnetic receiving antennae electrically connected to one another and each being arranged in proximity to the electromagnetic radiator such that lines of flux of the alternating magnetic field link the first and second receiving antennae; determining the amplitude of a second electrical signal induced in the first and second receiving antennae; monitoring a parameter of the first ac electrical signal supplied by the oscillator circuit, wherein said parameter varies with the proximity of said object and said electromagnetic radiator; and adjusting the determined amplitude of the second electrical signal in dependence upon the monitored parameter of the first ac electrical signal in order to compensate for changes in parameter of that first ac electrical signal caused by the presence in the proximity of the electromagnetic radiator of the object to be investigated. - View Dependent Claims (10, 11, 12, 14)
-
Specification