Airflow Monitoring - Bosch FAS-420-TM-R Operation Manual

Aspiration smoke detector LSN improved
Change of direction
Elbows and bends in the pipe system increase flow resistance. Therefore, they should only be
used where they cannot be avoided for structural engineering reasons. Light change of
direction (e.g. with 90 ° pipe bends or air sampling hose) are already approved as part of the
project according to EN 54-20 or ISO 7240-20 and need not be considered further.
Notice!
Pipe bends must be given preference over pipe elbows. Too many bends and pipe elbows
reduce the air speed in the aspiration pipe, thereby increasing the detection time.
A 90° pipe elbow corresponds to a straight pipe length of 1.5 m. Because of this, the
maximum total length of the pipe system is reduced by 1.5 m.
Testing
For critical applications, test the secure detection with activation attempts. Check also
whether there is airflow at the individual air sampling openings.
Notice!
In order to increase transport speed in critical application areas, the fan voltage can be
increased from 6.9 V to 9 V.
4.3

Airflow Monitoring

EN 54‑20 or ISO 7240-20 requires the detection of a 20-percent change in the airflow volume
by the detection module's airflow sensor. In order to achieve this, the activation threshold of
the airflow sensor must be set to less than or equal to 20%. It is recommended that airflow
calibration is carried out dependent on air pressure for both of these settings. In systems that
do not need to comply with EN 54‑20 or ISO 7240-20, any threshold can be set. The airflow
monitoring of the smoke aspiration pipes is planned taking into account the applicable
national regulations for the country concerned.
Adapting the airflow sensitivity
The sensitivity of the airflow sensor must be adapted to the application. Breakages and
obstructions must be accurately detected in the event of a malfunction.
The trigger threshold, and thus the sensitivity of the airflow sensor, can be set from 10 to
50%.
Activation threshold
Sensitivity
Notice!
Selection of the largest possible, precisely still-approved level is recommended.
Dynamic airflow sensors
The airflow monitoring of the unit makes it possible to detect breaks at the end of pipes and
identify sudden obstruction of individual air sampling openings (e.g. following tampering with
the pipe system). If the dynamic airflow sensors were activated via the diagnostic software,
note the following restrictions.
Restrictions
Airflow monitoring may only be set to level I if
Bosch Sicherheitssysteme GmbH
Complies with EN 54‑20 or ISO 7240-20
10% 20%
Very high High
Operation guide
Planning | en
40% 50%
Average Low
2020.04 | 5.1 | F.01U.088.878
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