| 摘要 |
PROBLEM TO BE SOLVED: To detect simply rotational frequency with high accuracy by providing a magnetic detecting means operated by the magnetic force of a magnetic near the magnet provided with a rotary shaft and covering a portion of the magnet with a yoke. SOLUTION: A cylindrical magnet 3 is attached to a rotary shaft 2 and a half of the magnet 3 is covered with a metal yoke 7 provided in the inner periphery of the press fit part of the rotary shaft 2 and the magnet 3. When the yoke 7 covers the magnet 3, the magnetic line of force emanated from the magnet 3 passes through the yoke 7, so that it is hardly emanated. Thus, a reed switch 6 provided near the magnet is operated once at one time of potation of the magnet 3 by the magnetic line of force, so that the rotational frequency can be detected with the read switch 6 by mounting the yoke 7 even to the magnet generally magnetized and the rotational frequency can be detected by a simple constitution with high accuracy. |
