| 摘要 |
<p>An alarm initiator (1) contains an operating contact (11) which is connected via a special line (10) to a telephone exchange (CT). The contact allows power to be applied to a relay coil (12) to operate its contacts (120,121) in the subscriber circuits to the firemen and also to provide the excitation circuit (40) to a warning signal generator (4). In each subscriber line circuit is the coil of a relay (33) which operates one contact set (34) to connect a capacitor (37) across the line circuit. This capacitor simulates the capacity of the line loop including the subscriber telephone (2). This ensures that the warning signal transmission is not upset when the telephone handset is lifted for use. A warning signal generator (5) at the subscriber telephone installation contains a detector which ensures that a high frequency generator produces an audible warning signal when an alarm call is made.</p> |
