| 摘要 |
PURPOSE:To prevent an unauthorized use by adding a weak magnetic field before recording information is read. CONSTITUTION:At the core 24 of a magnetic head 20, a coil 26 for reading card recording information exists and the obtained detecting signal is sent through an amplifying circuit 28 to a differentiating circuit 30 for detecting a peak. For the differentiating signal of the circuit 30, the reading signal of card recording information is obtained through a demodulating circuit 32. For the amplifying signal of the circuit 28, a timer signal is supplied through a waveform shaping circuit 34 via a timer circuit 36 to a timer circuit 38. A bias coil 42 is conducted through a bias circuit 40 by the timer of the circuit 38. By the conducting, a weak magnetic field is added to a magnetic card. Thus, since the unfair information is erased by the weak magnetic field during the reading of the recording information, the unauthorized use can be prevented.
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