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Product Information 500 Series LSN Fire Detectors (EU)
1.3. Functional Description of the Sensor Technology
Optical sensor (smoke sensor)
The optical sensor (Fig. 1., Pos. 1) operates according to the scattered light principle.
The LEDs (Fig. 1., Pos. 3) transmit light at a defined angle into the measuring area
(Fig. 2., Pos. 7). In case of fire, the light is scattered by the smoke particles and strikes
the photo diodes (Fig. 1., Pos. 2), which transform the quantity of light into a propor-
tional electrical signal.
The effects of daylight and commercial lighting sources are filtered out with an optical
daylight filter and by the use of electronic filtering and phase−locked rectification (am-
bient light stability: glare test DIN EN 54−7).
The various light−emitting and photo diodes of the detector are individually activated.
Consequently, signal combinations are produced that are independent of each other
and ideally suitable for the detection of smoke, which makes it possible to differentiate
between smoke and interference agents (insects, objects). In addition, the time char-
acteristics and the correlation of the optical sensor signals for the fire or interference
detection are evaluated.
Moreover, plausibility checking of the various signals makes it possible to detect errors
in the evaluation electronics and the LEDs.
Chemical sensor (CO gas sensor)
The gas sensor (Fig. 1., Pos. 4) detects mainly the carbon monoxide (CO) that is pro-
duced by a fire, but it also detects hydrogen (H) and nitrogen monoxide (NO).
The basic measuring principle is CO oxidation on an electrode and the measurable current
that arises from this. The sensor signal value is proportional to the concentration of gas.
The gas sensor supplies additional information in order to reliably suppress the distur-
bance variables.
The CO sensor is monitored by supervision of the internal capacity. If the capacity lies
outside the permitted range, a malfunction signal is output on the fire panel. In this
case, the detector continues to operate purely as a scattered light smoke detector.
Pollution sensor
The contamination level of the detector surface is measured and evaluated continu-
ously by the pollution sensor (Fig. 1., Pos. 6). A three−stage contamination display can
be read out at service (see Chapter 7.1.).
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PI − 34.70 en
BDL−F.01U.025.876
A5.en/ 02.02.2006
ST−FIR/PRM1 / zab
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