Fire Alarm Control Panel 22
Fire Alarm Control Panel 22 : System Functions: (7) Alarm Circuit Supervision: Various forms of alarm circuit supervision have been used to indicate trouble with an alarm circuit. Possible alarm circuit faults on a two wire circuit include one of the conductors being shorted to ground, open circuit (conductor continuity break), or a short circuit between the conductors. Also the circuits could be tampered with by having an external AC or DC voltage applied with various duty cycles or waveforms. There are a number of US patents that address this issue and some have been implemented in available system products. One of the first to address this issue was Patent No. 3,588,890 "Resistance Sensing Supervisory System" issued on June 28, 1971 and assigned to General Motors Corporation. General Motors used this supervision on all circuits installed in GM plants starting in 1970. An improvement to this basic "Resistance Sensing Supervisory System" can be obtained by providing a pulsed or time dependent variable voltage applied to the alarm circuit and is addressed in US patent numbers 4,030,095 and 4,716,401
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