Method of detecting particles by detecting a variation in scattered radiation
View Patent ↗A smoke detecting method which uses a beam of radiation such as a laser ( 16 ), to monitor a region, such as a room ( 12 ). A camera ( 14 ) is used to capture images of part of the room ( 12 ), including a path of the laser beam. Particles in the laser beam scatter light ( 30 ), and this is captured by the camera ( 14 ) for analysis. A processor ( 20 ) extracts data relating to the scattered light ( 30 ) to determine the density of particles in the beam, to determine the level of smoke in the region. The laser may have a modulated output ( 38 ) so that images captured without the laser tuned “on” can be used as a reference point and compared to images taken with the laser turned “on”, to assist in determining the level of scattered light ( 30 ) compared to ambient light. Filters ( 24, 26 ) may be used to decrease signals generated from background light.
1. A method of detecting smoke within a monitored region:
directing a beam of radiation across the monitored region;
capturing images of monitored region, including at least part of a path of the beam of radiation through the region;
analizing the captured images to determine the presence of smoke on the basis of an increase in light scattered from the beam;
integrating intensity values from the images;
determining individual smoke levels for a respective plurality of portions of the monitored region using the integrated intensity values and different thresholds for each portion, each of the smoke levels being based on an increase in light scattered from a portion of the beam within a corresponding portion of the monitored region.
2. The method of claim 1 . wherein the method includes simulating a plurality of point detectors corresponding to different segments of the beam.
3. A method as claimed in claim 1 wherein the method includes, outputting a smoke level to an addressable fire panel.
4. A method as claimed in 2 wherein the method includes, outputting a smoke level corresponding to a plurality of point detectors to an addressable fire panel.
5. A method as claimed in claim 1 , wherein the method includes dividing each image into subregions corresponding to said portions of the monitored region, each subregion including a corresponding portion of the path of the beam.
6. A method as claimed in claim 1 which further comprises adjusting a level of light received by the image capture device for each pixel by a predetermined scattering gain corresponding to a radius from the light source and scattering angle, θ.
7. A method as claimed in claim 1 which further includes:
integrating over a plurality pixels corresponding to the portion of the monitored region to obtain a detected obscuration for the portion of the monitored region.
8. A method as claimed in claim 1 which includes determining an integration region that contains the path of radiation.
9. A method as claimed in claim 8 which further includes:
performing background cancellation of the images of the integration region.
10. A method as claimed in claim 9 wherein the beam of radiation is modulated, and background cancellation includes summing n “on” frames and m “off” frames.
11. A method as claimed in claim 1 which includes modulating the beam of radiation and low-pass filtering a plurality of captured images to remove interference that is not correlated with the beam modulation and retain light scattering information.
12. A smoke detection apparatus for monitoring a region, comprising:
an emitter for directing a beam of radiation comprising at least one predetermined characteristic into the region;
an image capture device arranged to capture a plurality of images of the monitored region;
a processor for analyzing the plurality of images according to a method of claim 1 .