SMOKE SENSOR

PURPOSE:To obtain a sensor which has high detection sensitivity to suspended particles and detects the occurrence of an initial fire distinctively from operation dust by generating a 1st warning when the particle concentration of large-diameter suspended particles reaches a 1st particle concentration threshold value or a 2nd warning when the particle density reaches a 2nd particle concentration threshold value by specific times. CONSTITUTION:The air in a clean room enters a detection sensor 1 from its entrance 1a through the operation of a suction pump 2 and is discharged from its exit 1b. Suspended particles 3 scatter light from a lamp 4 and a photodetecting element 5 converts the scattered light into an electric signal. A comparator 9 compares this signal after amplification 7 with a particle diameter threshold value set by a particle diameter threshold value setter 8 and outputs a pulse when the output of the amplifier 7 is larger than the threshold value to detect large-diameter suspended particles. A controller 2 compares the particle concentration of the large-diameter suspended articles which is the output of a pulse counter 10 with the 1st and 2nd particle concentration threshold values set by a particle concentration threshold value setter 13 to generate the 1st warning by a warning device 15 when the particle concentration reaches the 1st threshold value or the 2nd warning when the concentration value reaches the 2nd threshold value by the number of specified times set by a frequency setter 14.