| 摘要 |
PURPOSE:To enable a highly accurate selection of material without use of any strong a.c. electromagnetic field by detecting the attenuation of the a.c. magnetic field of varied frequencies due to an electromagnetic induction to reference a attenuation map. CONSTITUTION:An a.c. magnetic field of varied frequencies - 14kHz, 70kHz and the like - from a generation coil 1 is attenuated due to an electromagnetic induction of a metal 3 to be selected. Different attenuations are detected through a detection coil 2 according to the frequency of the a.c. magnetic field in terms of the material, thickness and the like and referenced to a quadratic attenuation map 7 memorized in a memory section 7 to determine the material, thickness and the like with a discriminating section 6. This eliminates need for discrimination depending on a slight difference in the a.c. magnetic field attenuation of single frequency thereby enabling a highly accurate selection of material without use of any strong a.c. magnetic field. |
