| 摘要 |
PURPOSE:To enable accurate measurement while eliminating the need for working of a magnetic disc mounting surface and elevating area accuracy thereof, by arranging detectors facing each other on both sides of the disc and a signal synthesization means for synthesizing signals therefrom. CONSTITUTION:On both sides of a magnetic disc 1, signals S1 and S2 outputted from magnetic detectors 2a and 2b by vertical magnetization are amplified with first-stage amplifiers 5a and 5b to form a synthetic signal S3 synthesized by a connection P. The, the synthetic signal is deformed to a pulse Sp with a waveform shaping circuit 6 having threshold levels +V and -V determined so as to be free from effect of noises and counted with a counter 7. In this case, as the detectors 2a and 2b work complementarily against the swing of the magnetic disc 1, counts of the counter 7 is not affected by the swing of the magnetic disc 1. This enables the determination of correct rotation value while eliminating the needs for working a mounting surface of the magnetic disc and elevating the surface accuracy of the magnetic disc.
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