Bosch FCH?320, Operation Manual

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en | System Overview

Conventional Automatic Detectors

F.01U.002.707 | 8.0 | 2011.10

Operation Guide

Bosch Sicherheitssysteme GmbH

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System Overview

2.1

Configuration of the Detector

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 (refer to 

Figure 2.1

, item 1); 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 (refer to 

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 detector class set, the temperature sensor switches to an alarm state if the 

maximum temperature exceeds 54 °C (thermal maximum) or a defined temperature increase 

within a particular timeframe (thermal differential).

2.2.3

Chemical Sensor (Gas 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

1

Smoke measurement chamber with 

optical sensor

Figure 2.1

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

MS 400 / MS 400 B Base

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4

5

2

1

3

The gas sensor (refer to 

Figure 2.1

 and 

Figure 2.2

, 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 deception variables.

Figure 2.2

Chemical Sensor

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