Technical data

6 en | System Overview
Automatic Fire Detectors LSN improved
version
F.01U.003.449 | 7.2 | 2010.05 Product Information Bosch Sicherheitssysteme GmbH
2 System Overview
2.1 Detector Configuration
2.2 Functional Description of the Sensor Technology
2.2.1 Optical Sensor (Smoke Detector)
This optical sensor utilizes the scattered-light method.
An LED sends light into the measuring chamber (see Figure 2.1, item 1), where it is absorbed
by the labyrinth structure. In the event of a fire, smoke enters the measuring chamber. The
light is scattered by the smoke particles and hits the photo diodes, which transform the
quantity of light into a proportional electrical signal.
The DO detectors have a dual optical sensor that uses the different infrared and blue light
wavelengths (Dual Ray technology). This allows fires to be detected early and even the
smallest quantities of smoke (TF1) to be reliably detected.
2.2.2 Thermal Sensor (Heat Detector)
A thermistor (see Figure 2.1, item 2) in a resistance network is used as a thermal sensor; an
analog-digital converter measures the temperature-dependent voltage at regular intervals.
Depending on the specified detector class, the thermal sensor triggers the alarm status when
the maximum temperature of 54 °C or 69 °C is exceeded (thermal maximum), or if the
temperature rises by a defined amount within a specified time (thermal differential).
2.2.3 Chemical Sensor (Gas Sensor)
1 Smoke measurement chamber with
optical sensor
Figure 2.1 Detector Configuration
2 Thermal sensor
3 Chemical sensor (covered on the cross-
section)
4 Individual display
5 PC board with evaluation electronics
6 MS 400 Detector Base
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The gas sensor (see Figure 2.1, item 3) detects mainly the
carbon monoxide (CO) that is produced by a fire, but it also
detects hydrogen (H) and nitrogen monoxide (NO).
The underlying measurement principle is CO oxidation and
the measurable current that it creates. The sensor signal
value is proportional to the concentration of gas.
The gas sensor supplies additional information in order to
reliably suppress disturbance variables.
Figure 2.2 Chemical sensor
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