Principle Of Operation - DEKON D-BM100 Installation And Maintenance Manual

DEKON D-BM100 OPTICAL BEAM
SMOKE DETECTOR
Fig. 1 D-BM100 detector with prism reflector

PRINCIPLE OF OPERATION

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The D-BM100 detector consists of an infrared (IR) light transmitter and a receiver located in a single housing
and an interoperating separate D-BM50-1 prism reflector or D-BM100-4 set of reflectors. The detector
operation principle is based on continuous analysis of optical air transparency in the space between the
detector and the reflector (set of reflectors).
The detector can operate in one of four modes: supervision, alarm, fault – light beam interruption, and fault
– caused by contamination. If a certain, defined amount of aerosol (smoke) is found in the air, resulting in
reduction of optical transparency below a given (adjustable) threshold, then the detector enters the alarm
mode. Complete break of the beam (or its reflection due to an object occurrence in its optical path) is signaled
as a fault, because even the largest smoke concentration in the air does not cause a total break of the
detector optical path. When the air is clear, the detector is in the supervision mode.
Long lasting detector operation, especially in high dust level premises, may lead to contamination of optical
parts of the detector and the reflector/reflector panel. In order to maintain constant sensitivity and fire
detection ability during a long time, the detector is equipped with automatic compensation mechanism to
monitor its contamination and environment impact conditions. The circuits guarantee the same sensitivity
level in the whole compensation range. At a certain contamination level, the detector signals the fault mode
denoting a necessity to undertake servicing and cleaning works. However, even in this mode, the detector is
still able to detect smoke and trigger an alarm mode. A fault caused by high contamination requires cleaning
works of the reflector/set of reflectors and the detector front surface. After cleaning, the detector adjusts to
new conditions and automatically changes its mode from fault to supervision.
The D-BM100 detector's analysis functions are executed by a microprocessor. After the initial detector
optical path adjustment with built-in laser pointer is completed, the START button should be pressed. By
pressing this button, precise adjustment is being performed. At the same time microprocessor is analyzing
the ambient temperature and the settled sensitivity threshold. A self-adjustment program is switched on
after entering these data into the detector memory. The self-adjustment process is completed after achieving
a reference value with 5% tolerance. Finally, the decision criteria for fire alarm are drawn up for various fire
phenomena runs, for instance for fast or slow fire development. The data are kept in the detector non-
volatile memory and periodically checked. Any measured value change (against the assumed decision
thresholds) caused by a smoke, after triple verification, is treated by the microprocessor as a fire.
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