| 摘要 |
<p>One part (A) comprises a magnet (1) having a through-hole (1a) extending from one magnetic pole surface to the other, a first ferromagnetic plate (2) on one magnetic pole surface of the magnet, a magnetic shield plate (3) on the other pole surface and having an opening (3a) in register with the hole (1a) through the magnet (1). A casing (4) is formed of non-magnetic material. The other part (B) comprises a second ferromagnetic plate (7) adapted to be brought into magnetic engagement with the front part (A) adjacent the magnetic shield plate (3) at which time ferromagnetic contact member or members (5,8) complete a magnetic circuit connecting the two ferromagnetic plates (2,7) through the hole (1a) in the magnet (1).</p> |
