Siemens FDOOT221 Technical Manual page 28

3 Structure and function
Detector
28
Building Technologies
Fire Safety
Structure and function
1 Heat sensors
2 Backward scatterer
The detector has a sophisticated opto-electronic measuring chamber with two
optical transmitters, an optical receiver and two thermal sensors.
The transmitters illuminate the smoke particles from different angles. One sensor
acts as forward scatterer, the other as backward scatterer. The scattered light then
hits the receiver (photodiode) and generates a measurable electric signal.
The combination of a forward and backward scatterer facilitates an optimum
detection and the differentiation of light and dark particles, which leads to a
homogenous response behavior and optimizes the differentiation of wanted signals
and deceptive phenomena.
In addition, the heat sensors make it possible to detect fires without smoke
generation.
The combination of optical and thermal sensor signals optimizes detection
reliability. This has the following advantages:
Early detection of all types of fire, whether they generate light or dark smoke, or
no smoke at all.
The neural fire detector can be operated at a lower sensitivity level and thus
achieves a higher immunity against false alarms which may otherwise be
caused by cold aerosols (e.g. by smoking, electrical welding, etc.). In the case
of an open fire, the smoke sensitivity is heightened by the temperature
increase, which means that a detection reliability level that is comparable to
that of the wide-spectrum smoke detector can be achieved.
The neural fire detectors FDOOT241-x/-Ax can also be used either as purely
optical smoke detectors or pure heat detectors. This is possible by selecting one of
the following sensor modes (with the detector exchanger and tester or on the
control panel):
Sensor mode 0: Application as neural fire detector
Sensor mode 1: Application as heat detector
Sensor mode 2: Application as smoke detector
In sensor mode 1 or 2 the parameter sets of the heat detector FDT241 or of the
wide-spectrum smoke detector FDO241, respectively, can be selected. These
neural fire detectors then act in a similar way to heat detector FDT241 or smoke
detector FDO241.
1
4
3 Forward scatterer
4 Labyrinth
2
3
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01.07.2012