JPS6415897A - Fire sensor - Google Patents

Abstract

PURPOSE:To detect the location of fire occurrence by providing plural pieces of thermal sensors constituted of a junction surface where the optical axis shifts due to temperature variation in series connection to an optical fiber, and detecting the variation in the reflection loss of a laser beam by the thermal sensor. CONSTITUTION:The thermal sensors a A1-A4 are constituted in a manner that the optical fiber is cut and the cut ends brought into contact with each other so that the optical fiber axis will shift at the splicing part by the variation of temperature. These sensors A1-A4 are arranged in series to one piece of optical fiber B0. An electric pulse is converted to a pulse-shaped optical signal, which is made incident on the fiber B0. The incident beam is reflected by the thermal sensors A1-A4, the amount of loss of the beam is measured, and the loss amount is A/D-converted then stored in a digital memory. In the memory, the data of beam-loss amount at a normal time is separately stored. In case of a fire, the beam loss detected by the thermal sensor in the location of the fire increases, and this increased loss is compared with the data at normal time, and the location of the fire occurrence is thus detected.