INFRARED SENSOR SUITABLE FOR FIRE FIGHTING APPLICATIONS

Abstract: An infrared sensor which is particularly well suited for the detection of fires, consisting of an infrared detector (1), a filter to set the passing band (2), an optical assembly to pick up the signal (3), an electronic amplifier and signal processor (4), a sealed container (5) and a pedestal (6) which gives freedom of movement in elevation to the sensor itself. By adopting a suitable rotating platform and a signal processor, the sensor can be utilised to detect sources at temperatures 200 to 300 degrees C above an ambient temperature background. The data provided includes the direction of the signal detected, its amplitude and its time variation. The spectral sensitivity of the sensor is such as to offer an optimum application to the safeguarding of natural environments from the risk of fires: in standard weather conditions it is able to detect a six-meter fire at 10 km range.

Description: -4- Infrared sensor suitable for fire fighting applications Description This invention regards an infrared sensor which is particularly well suited for the detection of hot sources in the natural envi¬ ronment and it finds its logical application in the safeguard of forests from fires. Other applications are those of hangar and air strip surveillance in airports, the monitoring of urban refuse de¬ pots etc . Infrared sensors operating in the 1 to 2,5 micron wavelength al¬ though capable of detecting the signals coming from a fire, are subject to false alarms due to the variation of the solar ra¬ diation reflectivity of the ground or of the vegetation, while if sensitivity is extended beyond 4 or 5 micron, the ratio between fire signal and fluctuations of the ambient temperature background diminishes, making detection less probable. Illustration : Figure 1 shows a block diagram of the infrared sensor, where we can see: 1 infrared detector matrix; 2 interferential pass band filter; 3 refractive optics in crystal silicon; 4 electronic preamplifier; 5 hermetic container; 6 mechanical supporting device. For illustrative however not limiting purposes, the invention will now be described with reference to the Table attached, which shows a schematic outline of the system in the form of functional blocks . The infrared radiation is collected by a refractive optical unit 3 which has an aperture of the order of 50 mm diameter and high rela¬ tive aperture. The spectral transmission, in the system, is limited in a band range between 2,5 to 5 micron. Such limitation is obtained by suitable combination of the material which makes up the optical unit, of a spectral filter 2 and of the spectral response curve of the detector 1 itself. The utilization of silicon crystal optics, for example, requires the adoption of a filter which cuts the wavelengths less than 2,5 microns, while the cut off at wavelengths greater than 4 or 5 mic¬ rons is obtained by adopting a suitable detector (such as InAs) or by means of another filter if the bandwidth of the detector ex¬ tends beyond these wavelengths (such as the case of PbSe detectors) . The detector consists of a linear matrix of quantum, photovoltaic or photoconductive sensitive elements. The most suitable materials presently available are InSb, InAs, PbSe and HgCdTe; the sensitivi¬ ty required, taking into account the radiating sticking the detec¬ tor, is compatible with the adoption of a non cooled detector. The electronics 4, which follows the detector, provides the bias current, in the case of a photoconductive detector and the amplifi¬ cation of the signal itself. The sensor is housed in a sealed container 5. The container is fit¬ ted to a pedestal 6 which provides for elevation movement of the sensor itself. The field of view of the sensor is given by the di¬ mension of the single detectors, by the number of detectors pre¬ sent in the linear matrix and by the focal length of the optics. The typical application to the surveillance of forest fires are characterised by a field of view of each single detector equal to 1 degree and a total field of view equal to 15 - 20 degress (the matrix therefore includes 15 - 20 elements). The optimum use of the sensor is its integration within a forest fire surveillance system; a data collection centre manages a given number of detection centres consisting of a tower with a rotating platform carrying the infrared detector described above. The unique feature of this invention is in the adoption of an in¬ frared band within 2,5 and 5,0 micron within which the expected si¬ gnal due to a wood fire temperature is maximum and false alarms are minimized when due to solar reflections or thermal ' fluctua¬ tions of the ambient temperature background. *- •**« ■--- __> I -r i %_f B ____ £__._;£ii

Claims: Cl a i m s 1. Infrared sensor particularly suited for the detection of fires, consisting of a matrix of infrared detectors (1); a passband inter- ferential filter (2); a refractive optical unit (3); an electronic preamplifier unit (4); a sealed container (5) and a supporting me¬ chanical device. 2. Infrared sensor particularly well suited for the detection of fires, which may also be used in any situation, wherever a relati¬ vely uniform background is present and where hot sources have to be detected . SUBSTITUTE SHEET

Inventors: BROGI GIULIO, PIETRANERA LUCA, BROGI, GIULIO, PIETRANERA, LUCA
Applicants: SELENIA IND ELETTRONICHE, SELENIA INDUSTRIE ELETTRONICHE ASSOCIATE S.P.A.
Application year: 1990
Main classification: G08B17
IPC codes: G08B17