| 摘要 |
A smoke detector in which light from a blue source 3 is projected 7 into a detection volume 9. Radiation forward scattered at angles substantially less than 45‹, preferably 10‹ - 35‹, by particles in volume 9 is collected by ellipsoidal mirror 13 and focussed onto photodiode 15. In another embodiment an IR source 3A is added. Source modulation, alternate activation or sources &c. by control system 19 allows the control unit 20 to distinguish between blue and IR light reaching the photo detector, which then generates signals 21,23 based on the received intensity at each wavelength. These signals are compared 25 to determine the presence of smoke, as distinguished from dust water vapour &c. In another embodiment only blue light is emitted and detected, and the comparison/distinguishing circuitry is omitted. |
