version 4.7.2 – July 10th, 2022 Firmware version V2.1.7 and higher
EXXFIRE Installation and Service Manual 18
Aspirating smoke detection system
The system continually monitors the status within the protected space by taking air samples and
testing it for smoke. Air is drawn into the EXXFIRE
®
750CNF/1500CNF/2250CNF using a centrifugal
fan.
The air is filtered through a high-grade filter, which allows the broad range of smoke particles to
pass freely through, while preventing harmful dust ingress. This minimizes the chance of false
alarms caused due to solid particulates and insects, while maintaining a high throughput.
The carefully filtered air is then passed into the detection chamber, where three high-sensitivity
optical smoke detectors are exposed to the same sample. Each of the three calibrated detectors
can build up a reliable histogram of smoke obscuration data, and thus provide a reliable output in
its own right. This temporal reliability is then fortified by redundancy, by using the three detectors to
vote simultaneously. This provides an exceptionally reliable means to detect a fire, which reduces
false alarms, and avoids dropping the gas unnecessarily.
Air flow is monitored in line with EN54-20 (aspirating smoke detectors) to ensure that the inlet is not
blocked or broken, or that the filter is blocked. Either case will result in a fault status. Air flow is
monitored after the detection chamber, where it is then ejected through vents in the case –
sampled air is not returned to the protected space.
Software for decision making
The three smoke detectors are used to build up a picture of the current status of air in the protected
space. Three thresholds are defined in the software. As the smoke level rises above each threshold,
actions are taken accordingly. The thresholds and related actions are outlined in the following table:
Table 4 Smoke Thresholds and effects
The system also has an input for a Manual Activation Button (MAB). When this MAB is activated this
will also generate an Alarm, resulting in closing the ALARM relay, turning on the Alarm LED and
releasing the gas, just as when the smoke level surpasses the threshold value for Alarm.
Positive identification of a fire event – normally
connected to a central fire panel
Gas is released after this threshold is exceeded, after a
delay which can be programmed by the installer
depending on the application – it may be desirable to
allow the air conditioning fan to stop before ejecting gas
for example.
To Next Page
Loading...