| 摘要 |
An electronic alarm circuit for operating an audible alarm, such as a bell, has a trigger circuit arranged to continuously activate the alarm if a sensor is activated. The circuit also includes a capacitor arranged to be discharged if a normally closed test switch is opened. Closure of the test switch recharges the capacitor and renders the trigger circuit conductive. The alarm is thus activated but only for a restricted period dependent upon the time constant of the capacitor. Accordingly, it is possible to distinguish between a real alarm and the sound of the alarm when the circuit is tested.
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