AWACS™ Applications Pre-Alarm
108 NFS-3030 Programming Manual P/N 51345:C 11/4/03
detectors in its decision. Without statistical sacrifice in the ability to resist false alarms, Cooperative
Multi-Detector Sensing allows a detector to increase its sensitivity to actual smoke by a factor of
almost 2 to 1. Cooperative Multi-Detector Sensing also allows the combination of ionization with
photoelectric technology in reaching an alarm decision. The figure below shows a graph
representing Cooperative Multi-Detector Sensing:
Appendix Figure D-5 Cooperative Multi-Detector Sensing
D.3 Pre-Alarm
Definition
The Pre-Alarm function is a programmable option which determines the system’s response to real-
time detector sensing values above the programmed setting. Use the Pre-Alarm function if you
want to get an early warning of incipient or potential fire conditions. There are two levels of
Pre-Alarm:
•Alert (Refer to “Alert Level” below)
•Action (Refer to “Action Level” on page 109)
Alert and Action Pre-Alarm settings are set with point programming. Unique Pre-Alarm sensitivity
levels (PA) for individual detectors are listed in "Detector Sensitivity Settings" on page 109.
The LEDs on detectors polled in FlashScan mode will light steady green when in pre-alarm.
Alert Level
Alert Functions
The control panel software, in addition to checking for alarm levels, checks for Pre-Alarm
thresholds for each addressable, intelligent smoke detector programmed for Pre-Alarm. If a
detector’s real-time sensing level exceeds the programmed Alert threshold, the control panel
indicates an Pre-Alarm condition for the detector. The control panel does the following functions
when a detector reaches pre-alarm level:
•The Pre-Alarm message is sent to the History buffer and to installed printers. The message is
sent (and time stamped) at the time that it first occurred. This historical data could provide
valuable information about the progress of a fire.
•The
PRE-ALARM LED flashes and the panel sounder pulses until acknowledged.
•Zone Z000 (general alarm) or any other zone and the System Trouble and System Alarm
relays do not activate.
•The Pre-Alarm indication for this detector will restore automatically to normal if its
sensitivity, programmable to one of nine settings, drops below pre-alarm level.
•A subsequent alarm for this detector also clears the Pre-Alarm indication.
SMOKE OBSCURATION
Time (minutes)
Alarm
Combined
3 Sensors
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