Alarm system having improved control of notification appliances over common power lines

摘要

An alarm system which includes multiple notification appliances for signaling an alarm condition. The system controller intelligently controls the notification appliances including notification devices such as an audible or visual alarm through multi-bit digital messages sent over common communication lines. The alarm system has both a supervisory or standby mode and an active mode of operation. In the standby mode, the notification appliances are powered at a first polarity DC voltage. In an active mode of operation, the first polarity voltage is reversed (or forward biased) to energize all the notification appliances on the communication lines. The system controller controls operation of the visual alarms by issuing synchronization signals, wherein the line voltage drops to zero, which trigger the visual alarms. An audible alarm command signal is embedded within the synchronization signal to control operation of the audible alarm.