Patent ID: 8253578

Claim:
A smoke sensor of sound wave type, comprising: a sound wave generating unit that provides a sound wave to a monitoring space; a control unit that controls the sound wave generating unit; a sound wave receiving unit that receives the sound wave from the sound wave generating unit via the monitoring space; and a signal processing unit that detects an abnormality of the monitoring space by using an output of the sound wave receiving unit, wherein the signal processing unit comprises a smoke density estimation unit that estimates a smoke density in the monitoring space on the basis of a difference between the output of the sound wave receiving unit and a standard value, and a smoke density determination unit that determines the abnormality on the basis of a result obtained by comparing the smoke density found by the smoke density estimation unit with a predetermined threshold, wherein the sound wave generating unit has a function of providing a plurality of sound waves that have different frequencies, the signal processing unit comprises: a storage unit that stores data representing a relationship between the output of the sound wave receiving unit and a frequency of the sound wave provided by the sound wave generating unit that has been examined in advance under a plurality of test conditions that differ in a type of smoke present in the monitoring space and a smoke density; and a smoke particle determination unit that determines the type of smoke particles present in the monitoring space by using the data of the storage unit and the output of the sound wave receiving unit obtained by providing each of the plurality of sound waves to an actual monitoring space, and the smoke density estimation unit estimates the smoke density in the monitoring space when smoke particles determined by the smoke particle determination unit are identical to particles determined in advance as a monitoring object.