| 摘要 |
<p>PURPOSE:To make it possible to discriminate not only the presence or amount of an article, but also the kind thereof, by fitting a marker to the article. CONSTITUTION:A magnetic marker 20 different in permeability from one another being stuck on each article, an article 21 is made to run on a belt 15, while an AC voltage of a prescribed frequency is impressed on a coil 17 to generate an AC magnetic field. When the magnetic marker 20 passes through an AC magnetic field band 22, the magnetic marker 20 is magnetized and a magnetic flux is generated. By this magnetic flux the substantial inductance of the coil 17 is varied, the resonance frequency of a resonant circuit composed of the coil 17, a capacitor and a resistor is shifted and the value of a current flowing through the resonant circuit is varied. Since the magnitude of the magnetic flux generated by each magnetic marker 20 different in permeability from others is different, the variation in the inductance of the coil 17 is different for each magnetic marker 20 and the maximum variation in the value of the current flowing through the resonant circuit is also different for each magnetic marker 20. This maximum variation in the current value is read and compared in an electronic circuit element 18 and thereby discrimination of the article 21 is enabled.</p> |
