Function - Siemens FDF241-9 Technical Manual

3.3 Function

Building Technologies
Fire Safety
The flame detector detects infrared radiation. The spectrum of organic material
fires is very high near the A-channel (see diagram). Full use is made of this for
detection as the flame detector measures and evaluates radiation in this spectral
range. The description below explains how the sensory of flame detector impacts
on detection.
Sensory
Flame detector FDF241-9 has three sensors:
Pyroelectric sensor A measures the infrared radiation in the characteristic CO
spectral range between 4.0 and 4.8 µm (A-channel).
Pyroelectric sensor B measures the infrared radiation of deceptive phenomena,
such as hot objects (3), in the range between 5.1 and 6.0 µm (B-channel).
Sensor C is a silicon photo diode and measures solar radiation (2) in the range
between 0.7 and 1.1 µm (C-channel).
The infrared radiation of the sun, hot objects and organic material fires has
different spectra.
Thanks to these characteristics and the three sensors, flame detector FDF241-9
can use ASAtechnology to distinguish between deceptive phenomena and real
fires. Flame detector FDF241-9 is suited to use in environments with deceptive
phenomena, such as solar radiation or hot motors.
The following diagram shows the spectra of solar radiation, hot objects and organic
material fires, in this example of an alcohol fire.
C
1
2
Figure 6: Spectra of solar radiation, hot objects and organic material fires
1 Radiation intensity [%]
2 Solar radiation
3 Hot objects
4 Organic materials fire
In this case: Alcohol fire
Structure and function
Function
A B
3
4
A A-channel
B B-channel
C C-channel
Wave length [ m]
3
2
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2018-06-28