Particle detector, system and method

1. A method of detecting particles comprising: emitting a beam of radiation into a monitored region; and

detecting a variation in images of the region with image capturing means such that the variation in images indicates the presence of the particles,

wherein the steps of emitting and detecting comprise determining an ON period of the beam of radiation and an exposure period of the image capturing means on the basis of a power level of the emitted beam.

2. A method as claimed in claim 1 wherein the method further includes, modulating the beam of radiation such that the ON period of the beam is synchronized with the exposure period of the image capturing means.

3. A method as claimed in claim 2 wherein the ON period of the beam is one of greater than, less than or equal to the exposure period.

4. A method as claimed in claim 1 wherein the beam is pulsed.

5. A method as claimed in claim 1 further comprising one or more of the following steps: providing an ON period of the beam in the range of about a few seconds to 0.1 msecs; providing a corresponding beam power level in the range of 1.18 mW to 500 mW.

6. A method as claimed in claim 1 wherein the image capturing means operates with a frame rate in the range between 25 and 100 frames per second and the beam is pulsed at a frequency in a range between 12.5 Hz and 50 Hz.

7. A method as claimed in claim 1 wherein the particles comprise smoke particles.

8. A method as claimed in claim 1 wherein the image capturing means comprises one or more image capture devices.

9. A method as claimed in claim 1 wherein the image capturing means comprises at least two image capture devices viewing the beam of radiation from opposing positions.

10. A method as claimed in claim 1 further comprising the steps of: providing a first beam emitter paired with a first image capture device; providing a second beam emitter paired with a second image capture device; monitoring the emitted beam of the first emitter with the second image capture device; and monitoring the emitted beam of the second emitter with the first image capture device.

11. A method as claimed in claim 10 wherein one or more of the first and second paired emitters and image capture devices are provided in one and the same mounting arrangement.

12. A method as claimed in claim 11 further comprising the step of: pre-aligning one or more of the first and second paired emitters and image capture devices.

13. A method as claimed in claim 12 wherein the step of pre-aligning comprises: setting a beam direction of respective emitters such that the beam emerges at a predetermined angle with respect to the centre of view of the corresponding image capture device.

14. A method as claimed in claim 13 wherein the predetermined angle is θ, the distance between respective emitter/image capture device pairs is D meters such that a distance between a target spot of the beam of the first emitter and the second image capture device is given by: S=D tan θ.

15. A method as claimed in claim 2 which further includes synchronising the emission of the beam of radiation and the image capturing means comprises:

emitting the beam of radiation at a pre-determined modulation rate;

identifying a radiation source, being the source of the beam of radiation, in one or more video images captured by the image capturing means; and

continually modifying the image capturing means frame rate to remain in synchronisation.

16. A method as claimed in claim 15 wherein the radiation source has a secondary light source mounted to it, said secondary light source comprising a wide angle of emission.

17. A method as claimed in claim 16 wherein the step of identifying the radiation source in one or more video images captured by the image capturing means comprises: flashing the secondary light source in a predetermined timing relationship with the modulation of the radiation source to facilitate locating the radiation source in the image capturing means image.

18. A method as claimed in claim 17 wherein the secondary light source flashes in one or more of: a periodic pattern; a pseudo-random sequence.

19. A method as claimed in claim 17 further comprising the steps of: providing the image capturing means with a frame rate that approximates an oscillation rate of an oscillator of the secondary light source; identifying the flashing secondary source; varying a phase of the image capturing means frame rate to maintain synchronization between the exposure period of the image capturing means and the flashing of the secondary light source.

20. A method as claimed In any one of claims 19 wherein a frequency of the secondary light source oscillator is altered to be one of: the same as; a multiple of; a sub multiple of an AC mains electricity supply frequency.

21. A method as claimed in claim 1 further comprising the steps of: determining a path loss measurement by recording the intensity of a target incident beam spot of the emitted beam within the captured image and; comparing the recorded intensity with a recorded intensity at a previous time.

22. A system for detecting particles in monitored region, including one or more light sources configured to at least periodically emit a beam of radiation into the monitored region, one or more image capture devices for collecting an image of the region being monitored during an exposure period, an image processor for determining a variation in the images to detect the presence of particles at a plurality of locations within the region wherein at least one of the duration and timing of the emission of the beam into the monitored region and exposure period are determined on the basis of a power level of the emitted beam.

23. A system for detecting particles as claimed in claim 22 wherein the emission of the beam is synchronised with the exposure period of the image capturing means.

24. A system for detecting particles as claimed in claim 22 wherein the beam is pulsed.

25. A system for detecting particles as claimed in claim 22 wherein the duration of emission of the beam into the region is in the range of a few seconds to 0.1 msecs; and the corresponding beam power level is in the range of 1.18 mW to 500 mW.

26. A system for detecting particles as claimed in claim 22 wherein the image capturing means operates with a frame rate in the range of 25 to 100 frames per second and the periodicity of emission of the beam is in a range of 12.5 Hz to 50 Hz.

27. A method as claimed in claim 1 wherein the ON period of the beam of radiation and an exposure period of the image capturing means is determined in accordance with an indirectly proportional relationship with the power level of the beam.