| 摘要 |
A remote control system has a control unit 10 which interrupts the mains AC waveform for a predetermined period immediately following a current reversal, and a detector 13 which senses the interruption to control a load 14, particularly a light that is connected to a mains powered smoke alarm assembly 11 which replaces a ceiling rose. The control unit 10 replaces a wall box switch and may selectively insert an interruption in each positive half cycle, the light 14 being on in the absence of such interruptions and turned off when an interruption is sensed. An interruption may additionally be inserted at the start of each negative half cycle, such interruptions being detected to provide an additional control function. Alternatively, control may be dependent on the duration of the interruption. A master interconnect unit (40, Fig.5) may create permanent 60 microsecond interruptions at the start of each positive half cycle, the master unit (40) feeding a plurality of smoke alarm and light systems each associated with a respective control unit 10 which selectively lengthens the interruptions, the light being turned off in response to detection of the longer interruption. If a smoke alarm detects smoke, it applies a DC alarm voltage to the mains wiring in the period when the supply is interrupted. On detection of this alarm voltage, the master unit (40) lengthens the interruptions even further, in response to which all the alarms 11 enter a test mode in which their sounders and lights 14 operate.
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