Long-range quasi-distributed high temperature sensing based on fiber Bragg grating imbedded in high thermal conductive sheath cable

In this paper, we experimentally demonstrate the potential of quasi-distributed high temperature sensor based on fiber Bragg grating (FBG) utilizing high thermal conductive sheath, which can be a cost-effective alternative for conventional distributed temperature sensors based on Raman, Brillouin, and Rayleigh scattering. A unique Fire Sensing Cable (FSC) used in this experiment is constructed from a 304 stainless steel sheath with 16 optical fibers imbedded in a conductive fluid. One of the fibers contains FBGs for temperature sensing. Total of seventy seven FBGs were serially inscribed with the spacing of six meter over the total length of 468 meter. FSC was heated by various hot zones formed by IR furnace and nitrogen heat nozzle, as the shifts of FBGs were monitored. Although FBGs were 6 meter apart each other, high therinal conductivity of the stainless steal sheath made it possible to check temperature change in the region between gratings. These preliminary results clearly show a high potential of FBGs combined with FSC in applications of quasidistributed fire sensing cables and monitoring systems.