Detection system to determine the transmissivity of a medium with respect to radiation, particularly the light transmissivity of smoke-contaminated air, for fire detection
First Claim
1. Detection system to determine the transmissivity of a medium to radiation comprisinga source of radiation (6, Ro, 33), a radiation transducer (7, 8;
- 32) providing an electrical output signal representative of radiation impinging thereon, means (9) providing an indication output upon change in the degree of transmissivity of the medium, and means (1, 3, 3'"'"') providing at least two paths of radiation from the source to the detector,comprising the improvement whereinsaid means providing said paths comprises a plurality of reflectors located to be impinged by the radiation in both said paths, said paths including said reflectors in different sequence, but with the same number of reflections, and having different total lengths between the source and the transducer so that change in the radiation transmissivity of the medium will affect attenuation of the radiation beams travelling along said respective paths differentially, due to their different lengths.
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Accused Products
Abstract
To eliminate sources of error in fire detection apparatus regarding variation of light output from a radiation cell, and to eliminate varying ambient conditions such as dust and dirt contamination of reflectors and transducers, the radiation is directed over at least two paths by reflectors which are located such that the numbers of reflections in the paths and the reflection points are the same, whereas the lengths of the paths are different, and evaluating the difference signal to obtain a measure of the density of the medium through which the paths extend, typically the transmissivity of air which may be contaminated by smoke. In one embodiment, reflectors are located in the corners of a polygon, one of the paths extending across the polygon, and the other path extending essentially circumferentially thereof.
43 Citations
20 Claims
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1. Detection system to determine the transmissivity of a medium to radiation comprising
a source of radiation (6, Ro, 33), a radiation transducer (7, 8; - 32) providing an electrical output signal representative of radiation impinging thereon, means (9) providing an indication output upon change in the degree of transmissivity of the medium, and means (1, 3, 3'"'"') providing at least two paths of radiation from the source to the detector,
comprising the improvement wherein said means providing said paths comprises a plurality of reflectors located to be impinged by the radiation in both said paths, said paths including said reflectors in different sequence, but with the same number of reflections, and having different total lengths between the source and the transducer so that change in the radiation transmissivity of the medium will affect attenuation of the radiation beams travelling along said respective paths differentially, due to their different lengths. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
- 32) providing an electrical output signal representative of radiation impinging thereon, means (9) providing an indication output upon change in the degree of transmissivity of the medium, and means (1, 3, 3'"'"') providing at least two paths of radiation from the source to the detector,
Specification