Principles of Operation
16
SharpEye
TM
IR3 Flame Detector User Guide
2.2.3
Limitations of IR-IR Flame Detectors
CO
2
in the atmosphere attenuates the radiation in this spectral band.
(Absorption and emission of radiation always occur in the same band.) As a
result, the greater the distance between the detector and the fire, the
weaker the intensity of the radiation reaching the detector is (i.e. the CO
2
attenuation increases). This phenomenon explains the limitations of the
existing IR-IR flame detectors in the market:
•
Detection distance is restricted to 33ft/10m only.
•
Their immunity to false alarm sources is limited.
2.2.4
Advantages of IR3 Technology
To overcome these limitations, SPECTREX devised an innovative concept of
utilizing an additional detection channel. Three channels collect more data
from the environment, providing a more accurate analysis and better
performance.
After careful investigation, 3 channels were selected which, when operating
jointly, provide optimal fire detection characteristics:
•
Channel 1
: 4.2
–
4.6µ
Fire - the CO
2
peak
•
Channel 2
: 4.0
–
4.2µ
Eliminates false alarms from high temperature sources
•
Channel 3
: 4.8
–
5.2µ
Eliminates false alarms from flickering of background radiation
Most IR sources which create misleading IR alarm stimuli, including the sun,
incandescent, and halogen lamps, electric arc discharges, electrical heaters,
etc., do not possess this unique spectral signature of fire.
The IR sensors of the detector respond only to flickering of radiation signals.
The signals are compared to a predetermined threshold. Processing of the
results from the 3 IR channels is performed by the board microprocessor.
The result is a much greater detection distance and a highly increased
ability to distinguish between fire and false alarms.
This sophisticated technology surpasses all other existing flame detection
techniques on the market today.
2.2.5
Modbus RS-485
For more advanced communication, the 20/20MI has an RS-485 Modbus-
compatible output that provides data communications from a network (up to
247 detectors) to a host computer on universal controller, for central
monitoring. This feature enables easy maintenance, and local or remote
diagnostic tools.
