Point Detector; Multi-Sensor Smoke Detector - Siemens OH720 Technical Manual

3.2 Point detector

3.2.1 Multi-sensor smoke detector

Building Technologies
Fire Safety
The multi-sensor smoke detector OH720 is a multiple criteria fire detector with one
optical and one thermal sensor.
Structure and function
1 Labyrinth
2 Optical transmitter
The detector has a high-quality opto-electronic measuring chamber. The
measuring chamber contains:
● One optical transmitter
● One optical receiver
● One thermal sensor
The transmitter lights up the smoke particles. The scattered light then hits the
receiver (photodiode) and generates a measurable electric signal.
In addition, the heat sensor makes it possible to detect fires in cases where no
smoke has been generated.
The combination of optical and thermal sensor signals optimizes detection
reliability with the following benefits.
● Early detection of all types of fire, whether they generate light or dark smoke, or
no smoke at all.
● The fire detector can be operated at a lower sensitivity level, thus achieving
improved immunity against false alarms which may be caused by cold
aerosols. In the event of an open fire, the smoke sensitivity level is raised by an
increase in temperature which makes rapidly burning fires easier to detect.
The multi-sensor smoke detector OH720 has two parameter sets: 'Robust' and
'Sensitive'.
The multi-sensor smoke detector is addressed by the control panel when first
switched on.
If a short-circuit occurs, the defective part on the detector line is located by the
control panel and isolated between two detectors. In addition, a loop line
installation ensures an optimum level of safety.
See also
 Multi-sensor smoke detector [➙ 31]
2BStructure and function
3
1
2
3 Optical receiver
4 Heat sensor
3
17BPoint detector
4
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2015-05-04