Aspiration smoke detector LSN improved Planning | en 37
Bosch Sicherheitssysteme GmbH Operation guide 2020.04 | 6.1 | F.01U.029.275
Setting the airflow sensitivity
Level Activation threshold Sensitivity
I Low (+/- 10% volume flow change) Very high
II Average (+/- 20% volume flow change) High
III High (+/- 30% volume flow change) Average
IV Very high (+/- 50% volume flow change) Low
Level I II III IV
Complies with EN 54‑20 or ISO
7240-20
Activation threshold Small Average Large Very large
Sensitivity Very high High Average Low
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). Because these dynamic airflow sensors are only active if level I was selected
for the airflow monitoring, the points outlined under "Level I restrictions" must be taken into
consideration.
Restrictions
Airflow monitoring may only be set to level I if
– planning was carried out in accordance with "single-hole monitoring"
– the airflow sensor was calibrated dependent on the air pressure
– and no larger airflow fluctuations can occur.
Air pressure differences
There must be equal air pressure along the length of the aspiration pipe.
Notice!
If the aspirating smoke detectors and the pipe system are positioned in areas with different
air pressures, the air aspirated by the FAS-420 must be returned to the pressure area of the
pipe system (see Air-Return Pipe for Pressure Areas and Atmospheric Loads).
4.4 Defining the response sensitivity
The sensitivity of smoke aspiration systems can be divided into certain fire sensitivity classes
in accordance with EN 54‑20 or ISO 7240-20. These fire sensitivity classes describe specific
examples of ways in which the systems can be applied. The permissible system plans given in
Standard Pipe Planning can be determined for each classification.Smoke aspiration systems
with a higher fire sensitivity class according to EN 54‑20 or ISO 7240-20 also satisfy the
requirements of the lower classes.
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