Research On The Performance Improvement Method Of Optical Fiber Distributed Temperature Sensing System Based On S Coding

Optical fiber distributed temperature sensing system(DTS),detecting the temperature of the continuous spatial,has more advantages than traditional electrical temperature sensor,for instance,strong environmental adaptability,resistance to electromagnetic interference,large detection range and high precision of temperature measurement.But the spatial resolution and signal to noise ratio(SNR)of DTS system are incompatible.Thus,the coding method is introduced.With the pulse width and intensity of the incident light invariable,the encoding method can effectively improve the SNR of the system.More importantly,it can reduce the superposition times of the system signal,which give rise to reduce the time of measurement and improve the real-time performance with the low temperature measurement error.The S coding method was introduced in the optical fiber-folded Raman DTS system to solve the problem of mutual restriction between spatial resolution and temperature accuracy.Furthermore,in order to solve the problem that the temperature measurement error is still large when using the cumulative average algorithm and the wavelet transform method.The system signal is processed by increasing the encoding length of the S coding,which can not only reduce the superposition times of the signal,but also can further reduce the temperature measurement error.The above method reduced the superposition times of the system from 20000 times to 1000 times.Besides,the average temperature measurement error was decreased from 1.7? to 0.07?.The combination of S coding method and the accumulative averaging algorithm was proposed to solve the poor time resolution in the single scale temperature measurement system,which can guarantee the temperature measurement error and reduce the measurement time and improve the real-time performance of the system.The influence of different system noises on the measurement time and temperature error is analyzed,and an optimal time measurement method was put forward.The relationship of noise level,superposition times and temperature error was studied,which provides a basis for the optimization of temperature demodulation time.The simulation results prove the effectiveness of the method.This method can provide reference for the selection of optimal superposition times when the temperature measurement error is certain and the noise level is known.In addition,a multi-scale temperature measurement method was proposed to further reduce the measurement time of the system.In this method,the variable pulse width laser is used as the light source.First,the temperature distribution on the whole fiber is measured in large scale and the temperature change region is obtained.Then by adjusting the pulse width of the laser to reduce the fiber scale,only the signal in the large scale temperature change region was calculated.The specific region of the temperature change was obtained until the temperature change position and the temperature are locked under the required spatial resolution.Simulation analysis proves that this method can reduce the measurement time,and provide another idea for improving the real-time performance of the system.