PRINCIPLES OF OPERATION
3
2. PRINCIPLES OF OPERATION
2.1 GENERAL
In order to optimise the detection of flames from hydrocarbon, the FV300 detectors analyse radiant
infrared energy at the peak carbon dioxide emission wavelength around 4.5µm. In a separate guard
channel, the detectors also sense additional wavelengths between 4.8 and 5.8µm to determine
whether the spectral content received possesses the signature of a real flame. The signal received
is further analysed to determine whether its modulation frequency has the irregular and quasi-
random characteristic of a flame within a pre-determined frequency band. A powerful Digital
Signal Processor (DSP) is continuously analysing the radiation signals to detect a fire.
2.2 ARRAY-BASED FLAME DETECTION
The field of view of the detector is scanned by a 16 by 16 array of highly sensitive pyroelectric
sensors. A sapphire convergent lens collimates the infrared energy onto the surface of the array. A
precise narrow band interference filter centred at 4.5µm then eliminates unwanted wavelengths.
If the signal received is of sufficient intensity to form a detectable image on several elements on
the array, called a cluster, the DSP analyses their frequency characteristic as well as their
correlation and spectral ratio with the signal present on the guard channel. A value representing
the instant probability that a real fire is present, results from this calculation. This probability
value is then analysed over a period of time to confirm whether a flame has been detected.
By using an array as the sensing component, the FV300 detectors are able to locate the angular
position of the fire within the field of view. The detectors use this information to provide
superimposed location information on a composite video output from an internal CCTV camera
and to signal the coordinates of this location on its field bus data output. The array, together with
its optical components and software intelligent interpolation gives the detector an angular
resolution of better than 0.5 degrees.
Array-based detection also enables the FV300 detectors to identify several separate radiation
sources within its field of view. For practical purposes, the number of separate detectable sources
that are reported has been limited to the four strongest, with information on these available on both
video and field bus outputs.
Fig. 2 Array Cluster
SINGLE ACTIVE
ARRAY CLUSTER
MULTIPLE ACTIVE
ARRAY CLUSTERS
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