US 2003/0164766 A1 · Metal detector

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).

Claims14

Dependent claims

A metal detector for detecting the presence of foreign ferromagnetic or electrically conductive articles in an object to be investigated, 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 said 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 said electromagnetic radiator such that lines of flux of the alternating magnetic field link the said first and second receiving antennae;
a receiving antenna signal detector electrically connected with the said first and second electromagnetic receiving antennae and arranged to provide an output indicative of the amplitude of a second electrical signal induced in the said first and second antennae;
an oscillator circuit signal detector electrically connected with the said oscillator circuit and arranged to provide an output representative of a parameter of the said first ac electrical signal supplied thereby;
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 said first ac electrical signal caused by the presence in the proximity of the said electromagnetic radiator of the said object to be investigated.

4 more elements

A method for detecting the presence of foreign ferromagnetic or electrically conductive articles in an object to be investigated, 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 said electromagnetic radiator such that lines of flux of the alternating magnetic field link the said first and second receiving antennae;
determining the amplitude of a second electrical signal induced in the said first and second receiving antennae;
monitoring a parameter of the said first ac electrical signal supplied by the said oscillator circuit;
and
adjusting the determined amplitude of the second electrical signal in dependence upon the monitored parameter of the said 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 said electromagnetic radiator of the said object to be investigated.

3 more elements

Dependencies are inferred from the claim text.

Metal detector

Life of this patent

Metal detector

Life of this patent

Abstract

Claims14