| 摘要 |
PURPOSE:To eliminate tracking deviation due to the thermal expansion and contraction of a magnetic sheet and to perform excellent magnetic recording by providing a yoke made of a soft magnetic material with a Curie point of 60- 100 deg.C to the center part of the magnetic sheet. CONSTITUTION:A discoid center core 55 is fitted to the rotational center part of the magnetic sheet 2, and a PG coil 60 is provided to a recording and reproducing device opposite a PG yoke 50 embedded in the center core 55 of a jacket enclosure 1, thereby detecting magnetic pulse signals of the PG yoke 50 accompanying the rotation of the sheet 2. The soft magnetic material which loses its magnetism at 60-100 deg.C is used for the yoke material to prevent magnetic recording at high temperatures. Thus, undesirable recording and reproduction are eliminated with the simple constitution at high temperatures where tracking deviation is caused by the thermal expansion and contraction of the sheet.
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