Determining The Sensitivity - Siemens FDA2 Series Planning, Mounting

4.10 Determining the sensitivity

A6V11783979_en--_a
The sensitivity for the alarm threshold is set on the aspirating smoke detector. The
airflow, which is made up of the air from all the aspirating holes and the end caps,
is measured with this sensitivity.
The sensitivity at a specific aspirating hole is based on its proportion of the total
airflow. It is possible to calculate the sensitivity of a specific aspirating hole.
Example calculation: Sensitivity at an aspirating hole
The aspirating smoke detector has a sensitivity of 0.1 %/m obs.
The aspirating hole indicated (see arrow) supplies air making up 5 % of the total
airflow.
6.5 6.2 6 5.8
ASD
0.1 % /m obs
Fig. 16: Proportions of the total airflow supplied by the aspirating holes
a Sensitivity of the aspirating smoke detector
b Proportion of the total airflow
Result: Sensitivity of the aspirating hole indicated = 2 %/m obs.
Collective effect
If only one aspirating hole supplies smoke, the aspirating smoke detector detects
this with the calculated sensitivity. In the event of a fire, multiple aspirating holes
will usually supply smoke, which increases the sensitivity of the smoke detector
system.
If all the aspirating holes supply smoke, the sensitivity of the smoke detector
system corresponds to the sensitivity of the aspirating smoke detector. This
process is called the 'collective effect'.
[%]
5.7 5.5 5.4 5.2
a
0.1 % /m o bs
= 100 %
b 5 %
Planning
Determining the sensitivity
5.1 5 4.9 4.8 4.7
= 2.0 % /m obs
4
29.2
35 | 48