Fire alarm system with smoke detectors - has parallel contacts in closed loop and series failure contacts operating when alarm fails

摘要

The fire alarm system has smoke detector contacts coupled in parallel into the system loop line and failure contacts coupled in series into the loop between the detector contacts. The failure contacts operate when the alarm itself fails to operate and break the loop. The smoke detector consists of an optical coupler whose output drops when smoke is present and triggers a transistor that operates the relay whose contacts form the parallel detector contacts in the loop line. A second relay is operated if the warning light associated with the first relay fails to light. This second relay contacts are the failure contacts. The voltage in the loop line is monitored.