| 摘要 |
<p>PURPOSE:To discriminate detection signals one by one even when the signals are inputted at short intervals by digitizing the variation of a magnetic field due to the passage of a body to be inspected and weighting the size of foreign matter which can be identified for each body according to the size of the foreign matter. CONSTITUTION:In alternating magnetic fields nearby both sides of a primary coil 3, secondary coils 4 and 5 are arranged concentrically with a coil 3. Those coils 4 and 5 are so connected as to operate differentially, the difference between induced signals of the two coils 4 and 5 is detected, and the outputs of the coils 4 and 5 are amplified. The output side of the amplifier 6 is branched and connected to the input sides of multiplier detectors 7A and 7B. One signal which is branched behind an amplifier 2 as a reference signal is inputted to the detector 7A in in-phase relation. Further, the signal which is branched as the reference signal and further branched and shifted in phase by 90 deg. through a phase shifter 8 is inputted to the detector 7B. The outputs of the detectors 7A and 7B are inputted to sample and hold circuits 11A and 11B, whose outputs are A/D-converted and inputted to a controller 15 as a decision means through weighting circuits 14A and 14B.</p> |
