6 en | System Overview Conventional Automatic Fire Detectors
2021.03 | 11 | F.01U.004.377
User manual
Bosch Sicherheitssysteme GmbH
2 System Overview
2.1 Configuration of the Detector
1 Smoke measurement chamber with
optical sensor
Configuration of the Detector
2 Thermal sensor
3 Chemical sensor (covered on the cross-
section)
4 Individual display
5 PC board with evaluation electronics
6 Detector base
2.2 Functional Description of Sensor Technology
2.2.1 Optical Sensor (Smoke Detector)
The optical sensor uses the scattered-light method.
An LED sends light into the measuring chamber (item1); this light 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.
2.2.2 Thermal Sensor (Heat Detector)
A thermistor (item2) in a resistance network is used as a thermal sensor; an analog-digital
converter measures the temperature-dependent voltage at regular intervals.
The temperature sensor switches to an alarm state if the maximum temperature exceeds
54°C (thermal maximum) or if there is a defined temperature increase within a particular
timeframe (thermal differential).
2.2.3 Chemical Sensor (Gas Sensor)
The gas sensor (item3) 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 deception variables.
Chemical Sensor
2.3 System Description
Up to two detection principles are integrated into the FCP-320/FCH-320 Series Fire Detectors:
– Optical (for smoke): O
– Thermal (for heat): T
– Chemical (for gas): C
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