Reliability Analysis And Comparison Of Demodulation Methods For Raman Distributed Temperature Sensor

Distributed fiber optical sensor has been a hot spot in the world scientific community in recent years. In a distributed fiber optical sensing system, fiber plays the role of transmission channel and sensing medium. Compared with the electronic sensor system, it has a smaller size, lighter weight. And owing to their immunity to electromagnetic interference, the capability of handing much higher bandwidth and much higher sensitivity, the distributed fiber optical sensor has shown its unique advantages in the huge product chain.Raman distributed temperature sensor (RDTS) use fiber as the transmission medium. Based on the spontaneous Raman scattering, we acquired the power of backward Raman signal, which carrying the temperature information. After processing the data and removing the noise interference, the demodulated temperature curve can be obtained. Thus, the accurate temperature data can be got, too.In this paper, based on the Raman distributed temperature sensor, we conducted in-depth research on the reliability of three frequently-used Raman demodulation methods, the main work are as follows:1. The basic theory of Raman distributed temperature sensor has been analyzed. From both of the classic electromagnetism and quantum mechanics, the principle of Raman scattering have been discussed. Moreover, the principles of the three frequently-used Raman demodulation methods, including single-ended RDTS using Anti-Stokes signal only and using ratio between Anti-Stokes and Stokes and doule-ended RDTS using Anti-Stokes signal only, have been analyzed. Then, combing the optical time domain reflectometry (OTDR) and temperature demodulation methods, we achieved the measurements of distributed fiber temperature.2. The simulation of Raman distributed temperature sensor has been exhibited. In particular, the effects of reference temperature fluctuations, bending losses and variations of the attenuations at Anti-Stokes signal only on the sensing performance have been investigated at different temperatures. Based on the above three aspects, the reliability of the three frequently-used demodulation methods have been analyzed in experiment.3. The system architecture of the Raman distributed temperature sensor has been exhibited, including the working principle of the whole system, the selection principle of the main components, the key components finally chosen and the parameters of each selected device. Moreover, we use the networking technology to upload the data which data acquisition card collected to the server-side and stored in the database. Then we use the C# language to program and ultimately received the waveform display of temperature curve. Finally, we analyzed the important technical indicators and the function of each key sub-module.4. The experiment of the Raman distributed temperature sensor. Setting the reference temperature fluctuations as 1℃, the bending losses as 0.22dB and the variations of the attenuations at Anti-Stokes signal only as 0.22dB artificially, then we measured the temperature curve of the single-path, dual-path and loop-path demodulation methods, separately. The experimental and theoretical results have been compared, and then we got the reliability of each demodulation method.