| 摘要 |
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 ).
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