| 摘要 |
<p>PURPOSE:To easily detect the presence or absence of a packaged object like an instruction manual, etc., that is mixed with a commodity without unpackaging the commodity by providing a magnetic layer on the packaged object by dispersing the magnetic powder of a high magnetic permeability and low coercive force into a binder. CONSTITUTION:A DC magnetic field exciting part 100 consists of a DC voltage power supply 101, a voltage/current converter 102 which converter 102 which converts the DC voltage into a DC current, and an exciting coil 103 which generates a DC magnetic field by the DC current. A received signal detecting part 200 is placed against the coil 103 and consists of two receiver coils 201 connected differentially to each other, a differential amplifier 202 which amplifies the induced signal, and a comparator 203 which judges detection of the signal. The output of each coil 201 is usually equal to zero. However, the DC magnetic field is affected when a magnetic detection marker passes through a detection area, and the magnetic fluxes interlinking both coils 201 vary with a time difference so that voltage is induced at each coil and a differential output signal is acquired.</p> |
