| 摘要 |
An optical fire detector in which the beams are received in a detector after having passed through a measuring chamber, for determining if the intensity of the received beam has been affected by combustion aerosols. A prism system with two prism groups (1-6, 7-11) having mutually parallel planes is arranged to extend the beam path through the measuring chamber, so that a beam from one light source (31) incident on a prism in either of the prism groups is directed by total internal reflection towards a prism in the other group, and vice versa, until the light beam comes to a ray detector (30) via all the prisms in the system. An indication circuit (25-28) indicates that the difference between instant characteristic values of the reflected beam and corresponding values at a reference state exceed a threshold value. |
