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Pre-Alarm
36 AFP-300/AFP-400 Programming PN 50259:C1 06/19/97
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A unique feature of AWACS, Cooperating Multi-Detector Sensing is the ability of a
smoke sensor to consider readings from nearby sensors in making alarm or Pre-Alarm
decisions. Using fuzzy logic algorithms, each sensor can include up to two other
sensors in its decision. Without statistical sacrifice in the ability to resist false alarms, it
allows a sensor to increase its sensitivity to actual smoke by a factor of almost 2 to 1.
Cooperating Multi-Detector Sensing also allows the combination of ionization with
photoelectric technology in reaching an alarm decision. Figure 48 shows a graph
representing Cooperating Multi-Detector Sensing:
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The AWACS™ (Advanced Warning Addressable Combustion Sensing) feature also
provides the Pre-Alarm function to give 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 37).
Alert and Action Pre-Alarm settings are global—for instance, if Pre-Alarm is selected,
all intelligent detectors programmed for Pre-Alarm are set to Alert or Action. You can,
however, set unique Pre-Alarm Levels (PA) for individual detectors. Refer to “Detector
Sensitivity Settings” on page 39.
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The control panel software, in addition to checking for alarm levels if selected, checks
for Pre-Alarm thresholds for each addressable, intelligent smoke detector. If the
Pre-Alarm level exceeds the programmed Alert threshold, the control panel indicates an
Alert condition. The control panel does the following functions when a detector reaches
Alert level:
• The Alert message is sent to the history file and to the optional LCD-80 and printer.
The message is sent (and time stamped) only 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 F09 activates—but Zone 00 (general alarm) or any other zone, or trouble
relay or alarm relay does not activate.
• The Pre-Alarm indication for this detector will restore automatically to normal if
its sensitivity drops below Alert level. Zone F09 clears automatically when no
Pre-Alarm conditions exist.
• A subsequent alarm for this detector will clear the Alert indication.
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