Chemical Sensor (Gas Sensor); System Description; Flash Frequency And Error Detection; Features - Bosch FAP-DO420 Operation Manual

Automatic Fire Detectors LSN
improved
2.2.3

Chemical Sensor (Gas Sensor)

The gas sensor (see , page 6, 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.
2.3

System Description

Up to three detection principles are integrated in FAP‑420/FAH‑420 series detectors:
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The individual sensors are programmed via the LSN network manually or using a timer. All
sensor signals are analyzed continually by the internal signal analysis electronics (ISP) and are
linked with each other. By linking the sensors (combined detectors), the detector can also be
used in places where the work carried out gives rise to light smoke, steam or dust. If a signal
combination fits the selected identifier for the area of operation for the detectors, an alarm is
triggered automatically.
2.4

Flash Frequency and Error Detection

The LSN improved detector has two centrally positioned two-color LEDs that flash green to
display the operational status.
The green LED on LSN improved FAP‑420/FAH‑420 series detectors is deactivated when
delivered. It can be activated as required via the programming software.
The LSN improved detector permanently monitors and adjusts itself throughout its life cycle in
order to adapt its sensitivity to the set threshold value.
A message is sent to the fire panel if the detector becomes too contaminated.
The LED will start to flash red as soon as an alarm is triggered.
The detector will return to its normal operating condition when the alarm is canceled via the
control panel or if the alarm cause disappears.
2.5

Features

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Bosch Sicherheitssysteme GmbH
Optical (for smoke): O
Dual-optical (for smoke): DO
Thermal (for heat): T
Chemical (for CO gas): C
Active self-monitoring of the sensors, with display on the fire panel:
– Active adjustment of the threshold (drift compensation) if the optical sensor
becomes contaminated.
– Active adjustment of the threshold (drift compensation) of the chemical sensor.
EMC safety is 50 V/m in the 1-3000 MHz range and is therefore much higher than required
by VdS 2110 (VdS Schadenverhütung GmbH).
Preservation of LSN loop functions in the event of wire break or short-circuit of a detector
through integrated isolators.
Individual detector identification on the fire panel in the event of an alarm. Alarm
indication on the detector with a flashing red LED.
Programmable, i.e. can be adjusted to the area of operation.
Operation Guide
System Overview | en
3
Chemical sensor
12/2012 | 8.1 | F.01U.003.448
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