Bosch FAP-OC 500Series Informationen zum Produkt - Seite 8

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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ST−FIR/PRM1 / zab