| 摘要 |
An electromagnet is formed of a combination of an iron support, an iron piece, and a solenoid, and an interrupter is provided to intermittently excite said electromagnet. A cylindrical diaphragm, equipped with an armature so disposed as to come against said iron piece, covers said iron support so that said iron piece, said solenoid, and said interrupter may be enclose therein.
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