| 摘要 |
An optical fire detector in which a radiation source (4) generates a ray beam, which, after having passed through the air in a room, is received by a detector (5) for determining if the characteristic properties (intensity, modulation) of the received beam have been affected by combustion, generating aerosols or convection in the air. The fire detector includes a Fresnel lens (1) with two focal points, on one side of the room, the radiation source (4) being disposed at one focal point and the beam detector (5) at the other. On the other side of the room there is arranged a retroreflector (6), which by total internal reflection re-emits the beam sent from the Fresnel lens (1). An indicating circuit (11) connected to the radiation detector (5) indicates that the change in the characteristic values of the emitted and received beam exceed threshold value. |
