Airflow Monitoring - Bosch FAS-420-TM Operation Manual

36 en | Planning
3.3

Airflow Monitoring

EN 54-20 requires the detection of a 20-percent change in the airflow volume by the detector
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, 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
–
–
–
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 Section 2.6.4 Air-Return Pipe for Pressure Areas and Atmospheric Loads,
page 25).
NOTICE!
FAS-420-TM series detectors with active fire source identification must be installed outside
the areas to be monitored and without an air-return pipe.
F.01U.088.878 | 4.1 | 2010.11
Complies with EN 54-20
10%
Very high
planning was carried out in accordance with "single-hole monitoring" (see
Section 3.7 Planning with Single-hole Monitoring, page 44),
the airflow sensor was calibrated dependent on air pressure (Section 6.3.2 Air-Pressure-
Dependent Calibration, page 77)
and no larger airflow fluctuations can occur.
Operation Guide
FAS-420-TM Aspirating Smoke Detector
20% 40%
High Average
Bosch Sicherheitssysteme GmbH
50%
Low