PRINCIPLES OF OPERATION
4
Another advantage of array-based detection is that non-flame interferences, eg, black body or light
sources, can be uniquely identified to within an area of the field of view. This ability to separately
analyse signals from flame and non-flame sources enables array based flame detectors to not be
desensitised in the presence of non-flame interferences, unless such sources are physically
coincidental. It also enables a known but unwanted source of radiation that is likely to be present
in the field of view of the detectors, to be ignored by applying of a ‘software’ mask to the signal
processing but still detect fires in the rest of the area.
2.3 REJECTION OF NON-FLAME SOURCES
2.3.1 GENERAL
In a new concept for eliminating nuisance alarms from modulated blackbody and other unwanted
non-flame radiation sources, the FV300 employs a combination of multiple spectral analysis and
time domain analysis techniques.
2.3.2 BLACKBODY REJECTION
A measure of the radiated energy in the CO
2
emission waveband, between 4.4µm and 4.7µm, and
in a higher waveband, between 5µm and 5.7µm, provides a means to discriminate real flames from
blackbodies. Unfortunately, most fuels do not have a clean burn and, except for a distinctive peak
at the carbon dioxide emission wavelength, possess a characteristic more akin to that of a
blackbody, exhibiting the distinctive CO
2
atmospheric emission band as well as a significant
emission beyond 4.7µm.
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