Research On Demodulation And Positioning Method Of Large Capacity Fiber Bragg Grating Sensing

In today’s,optical fiber technology has been applied in all aspects of people’s lives.Fiber Bragg Grating(FBG)sensors have the advantages of small size,fast response,strong resistance to electromagnetic fields,easy networking and multiplexing,etc.,and have been widely used in civil construction,industrial engineering,aerospace and other fields.In view of the needs of large-scale projects,this subject studies the demodulation and positioning methods of large-capacity fiber grating sensing systems.This paper introduces the basic theory,sensing characteristics and multiplexing technology of fiber grating sensing.Based on the above three aspects as the theoretical basis,the current classical demodulation technology of fiber sensing is compared and analyzed.According to the requirements of practical engineering and the characteristics of fiber grating sensor,a demodulation scheme of phase-shifted pulse is determined.The main contents of this study include:(1)Aiming at the serious problem of crosstalk in large-capacity FBG sensing systems,the spectral signal is studied in two aspects: external noise and internal crosstalk: first,a signal denoising method with improved modal decomposition combined with threshold is proposed to suppress external noise;second A time-division multiplexing technique based on layer-by-layer compensation is used to suppress internal crosstalk.The analysis results show that the above two methods can reduce the influence of external factors on the spectrum and improve the accuracy of spectrum demodulation.(2)In view of the defect that the traditional Gaussian fitting algorithm is seriously affected by the type of spectrum,the wavelength positioning of the spectrum adopts a peakfinding algorithm combining Hilbert transform and Gaussian fitting.This method can handle both asymmetric spectrum and multi-peak spectrum.Can ensure good measurement accuracy.FBG addressing technology is a time-delay-based spatial localization method capable of scanning thousands of fiber grating sensors within 1s.(3)The experimental platform of the optical fiber sensing demodulation system was designed and built.According to the needs of the actual engineering for positioning monitoring,based on the three core parts of optical fiber sensing,signal demodulation and data processing,in different impact plate materials and Four groups of positioning monitoring experiments were performed under the initial conditions of different impact loads.The experimental results show that,ideally,the average positioning error of the system is within 3cm,which achieves the expected effect.