Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1991-10-21
1995-06-06
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
250342, 250349, 250353, G08B 1712, G01J 142
Patent
active
054224845
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an infrared sensor capable of detecting heat sources at temperatures of 200.degree. to 300.degree. C. above an ambient background temperature, typically those heat sources coming from a fire, while rejecting solar radiation reflections and fluctuations in ambient background temperature.
BACKGROUND OF THE INVENTION
Currently known infrared sensors which are used to detect infrared radiation coming from fires operate in the 1 to 2.5 micron wavelength. Although such sensors are capable of detecting infrared radiation generated by a fire, they are subject to false alarm conditions due to the variation of reflected solar radiation reflected off the ground or off vegetation in the area of detection of the sensor. If, however, the sensitivity of the infrared sensor is extended beyond to the 4 or 5 micron wavelength, the ratio between the infrared radiation from the fire and infrared radiation coming from fluctuations of the ambient background temperature diminishes, making accurate detection of the fire less probable.
It would therefore be greatly advantageous to have an infrared fire detector which is optimized for detecting fires against an ambient background temperature with reduced succeptability to false alarms due to the variation of solar radiation from reflected sources.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention is related to an infrared fire detector which is particularly well suited for the detection of heat sources in the natural environment, particularly from fires. It is generally intended for use in fire detection systems used to protect forests from forest fires. Other applications which are envisioned are those of hangar and air strip surveillance at airports as well as the monitoring of urban refuse depots, etc. Since the detector is particularly well suited for fire detection outdoors, it is envisioned that the sensor would find optimal use as a detection component in an integrated forest fire surveillance system.
The infrared detector of the present invention optimally detects heat sources in the infrared frequency band falling within about 2.5 to 5.0 microns. It is within this band that the infrared radiation due to wood fires is at its maximum, and therefore false fire alarms possibly triggered by solar reflections or thermal fluctuations of the ambient background temperature are minimized.
The detector is made up of an infrared sensor which receives infrared radiation which has been collected and focused by a refractive optical collection unit. Between the infrared sensor and the optical collection unit is a spectral filter have a pass band which is selected so as to optimize infrared detection of the system to a frequency band of between about 2.5 to 5 microns. The desired frequency band is obtainable through a suitable combination of materials which make up the optical collection unit, the spectral filter and the infrared response curve of the infrared sensor itself.
Suitable electronics are provided to provide bias current to the infrared sensor, if such sensor is, for example, of a photoconductive variety, and an amplifier is provided to amplify the signal coming from the infrared sensor to suitable levels for use in fire detection systems.
The infrared sensor used in the system may be implemented either as a photovoltaic or photoconductive sensor comprised of a single sensing element or it may be made up of a multiplicity of sensor elements arranged in a linear matrix. By arranging individual sensor elements in a linear matrix, the overall field of view of the sensor may be varied. For example, if each single detector element has a field of view of one degree, then to achieve a field of view of 15.degree. to 20.degree. the matrix would require 15 to 20 elements. Of course, the focal length of the optics would vary accordingly so as to insure correct collection and focusing of infrared radiation for the field of view selected.
The individual sensor elements may be photovoltaic or photoconductive sensors chose
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Brogi Giulio
Pietranera Luca
Alenia Spazio SpA
Glick Edward J.
Hannaher Constantine
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