| 摘要 |
A resettable switching device, e.g. a relay, comprises a fixed contact ( 18 ) and a movable contact ( 28 ). A solenoid ( 12 ) is fixed relative to the fixed contact and a ferromagnetic plunger ( 20 ) carries the movable contact. A spring ( 24 ) biases the plunger away from the fixed contact so the device is normally open. When the device is set a further ferromagnetic element, e.g. a plunger ( 22 ), holds the first plunger ( 20 ) in a closed-contact position by magnetic attraction against the action of the spring ( 24 ). When a predetermined current condition exists in the solenoid the magnetic attraction between the element and plunger is reduced below the level necessary to hold the plunger so that the movable contact disengages the fixed contact.
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