On the periphery of this detector there is a number entrances for introducing smoke into a black cavity, in which are placed a light emitter whose light is to fill the cavity itself, and a light receptor which receives light emitted by the emitter and scattered by the smoke. The arrangement of these two parts is in such a way that the axes of the light beams intersect at an angle of about 145 deg.Under such arrangement, light output meeting the detective sensitivity of UL standards can be obtained in grey smoke with an extinction coefficient of or under 4%/foot and in black smoke with an extinction coefficient of or under 10%/foot. |