PRINCIPLES OF OPERATION
5
To ensure that flames from all potential fuels are detected whilst minimising the risk of nuisance
alarms, an optimum spectral signature of a flame, defined by its ratio at the two measuring
wavebands (A/B in Fig. 4) has been established experimentally by lighting characteristic fuels at
different distances. This was compared with a similarly obtained blackbody ratio (C/D in Fig. 5),
enabling an optimum flame decision threshold to be defined.
In addition to the above spectral analysis, the modulated infrared energy seen by each activated
cluster of the array is further analysed for frequency irregularities over a period of time that would
be typical of that of a flame, but not a blackbody source. With this sophisticated level of signal
processing, the FV300 FlameVision range of detectors offers a high degree of immunity to all
blackbody sources likely to be present in the application.
Petrol fire
at 20m
3
3.5
4
4.5
5
5.5
6
A
B
Energy
Wavelength (m)
Fig. 4
Measured Flame Spectral Characteristics
Black body
1200 K at 2m
3
3.5
4
4.5
5
5.5
6
C
D
Energy
Wavelength (m)
Fig. 5
Measured Blackbody Spectral Characteristics
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