| Fiber optic sensing has the characteristics of strong resistance to electromagnetic interference,high sensitivity,good reliability,long transmission distance,and easy networking.It has unique advantages in safety monitoring under harsh conditions.Fiber optic sensing technology,with its performance and deployment advantages,can replace traditional electrical sensing technologies in many fields such as petrochemicals,electricity,and tunnel transportation.At present,fiber optic sensing technology has been widely used in the safety monitoring of subways,urban tunnels,power networks,natural gas pipelines,and other large facility buildings.Through in-depth research on the status quo of fiber Bragg grating(FBG)sensing technology at home and abroad,this paper takes the sensing mechanism of ultra-weak FBG as the research object,studies the demodulation technology of ultra-weak FBG sensor network,proposes a compound noise reduction technology and a new spatial positioning method for noise processing and peak seeking positioning,and finally forms a high-precision FBG demodulation method that can be applied to subway tunnel fire identification.This article analyzes several main noise sources in ultra-weak FBG sensing networks,and proposes a new composite noise reduction technique(HHT-LWT)based on the analysis of Hilbert Huang Transform(HHT)and Lifting Wavelet Transform(LWT)techniques.The simulation results show that this method not only improves the end effect and modal aliasing phenomenon in the denoising process,making the denoised signal closer to the original signal,but also maximizes the separation of noisy signals and improves system accuracy.In order to realize the spatial location of subway tunnel fires and solve the multimodal multi-objective optimization problems(MMOP)of ultra-weak grating arrays,this paper proposes a DIDE-FPP composite spatial location method based on distributed individuals differential evolution(DIDE)algorithm and four-point positioning(FPP).This method first uses the DIDE algorithm for peak finding,and then uses the FPP algorithm to form a composite spatial positioning method with three-dimensional spatial positioning capabilities.By comparing the performance with 13 advanced peak-finding algorithms,it is verified that the DIDE-FPP composite positioning peak-finding method proposed in this paper has a higher spatial resolution.Finally,a test platform for the temperature-sensing fire monitoring system of the subway tunnel was built.Through the temperature sensing experiment,it was proved that using the system built by the high-precision demodulation method proposed in this paper,the FBG temperature sensitivity was stable at 10 ± 1pm/℃ within the temperature test range of 20 ℃～70 ℃,and the spatial positioning accuracy could reach 10 cm.This method has certain theoretical reference and technical support significance for subway tunnel fire hazard identification and signal processing of grating array sensing demodulation system. |
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