| 摘要 |
<p>ALARM CONDITION DETECTING APPARATUS AND METHOD Alarm condition detecting apparatus in the form of a combustion products detection system for monitoring a zone to detect the occurrence of fire therein. The apparatus has a plurality of detecting units adapted to be interconnected as parallel loads with a control unit. Each detecting unit receives operating power which may be from the control unit and functions to monitor a selected portion of the zone, generating, as appropriate, condition signals indicative of condition normal, impending alarm, alarm or unit malfunction. The impending alarm and unit malfunction signals are preferably pulsed signals of distinctly different frequencies and a light emitting diode (LED) arrangement is included in the detecting units to generate visual outputs corresponding to the impending alarm, alarm and unit malfunction signals. The condition signals generated by the detecting units may be transmitted to and monitored by the control unit by the method of correspondingly changing the parallel load impedance thereacross to cause changes in a loop current flowing in the control unit. In response to such loop current changes, the control unit is adapted to appropriately indicate that the zone is in a normal state, an impending alarm condition, an alarm state, detecting unit malfunction or system trouble. To indicate alarm condition, the control unit latches in an alarm output state. The control unit has time delay circuitry to prevent latching into the alarm output state until an alarm condition signal of predetermined duration has been received.</p> |
