| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a fire sensor without causing any non-disaster report or erroneous report due to the influence of the directivity change of a sound wave resulted from the change of a sound speed in a monitoring space. Ž<P>SOLUTION: A sound pressure ratio calculation means 40 calculates a sound pressure ratio between first and second ultrasonic waves wherein the path length of transmission paths through which those ultrasonic waves are propagated from a sound source section 1 to a light receiving element 3 are different from each other. A sound speed measurement means 44 calculates the sound speed of a monitoring space, and a sound pressure ratio correction means 45 corrects the sound pressure ratio so that the fluctuation of the output of the sound pressure ratio calculation means 40 due to the change of the sound speed can be canceled. A smoke density estimation means 41 estimates the smoke density of the monitoring space by using the sound pressure ratio when the fluctuation due to the sound speed change is canceled. A fire determination means 42 determines the presence/absence of a fire by comparing the smoke density estimated by the smoke density estimation means 41 with a prescribed threshold. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
|
