多参数分布式光纤传感系统关键技术研究

发布时间：2018-05-01 09:26

本文选题：分布式传感 + 多参数　；参考：《重庆大学》2015年硕士论文

【摘要】：分布式光纤传感技术是利用光纤自身既作为信号传输介质又作为传感单元,从而获取整个光纤路径沿线的外部物理量的分布情况。分布式光纤传感系统测量精度高,传感距离长,并且具有较好的可靠性,现已广泛应用于长距离基础设施的健康监测。然而故障的发生通常表现为应变或振动事件,抑或是环境温度的改变等多种参量的变化,仅仅对单一物理量的监测并不能确保对事故进行有效的预警和定位,因而多参数的分布式测量也显得越来越重要,并逐渐成为分布式测量的一个发展趋势。目前国内外对于多参数的分布式测量主要集中在应力及温度的同时测量,该原理是利用拉曼散射的温度效应及布里渊频移随应变及温度的变化量来实现。而对于分布式振动及温度的同时测量还鲜有报道,本文结合瑞利散射及自发拉曼散射的OTDR系统实现了振动及温度的分布式测量,并采用脉冲调制的方式获得了高信噪比的拉曼散射信号,又避免非线性产生给测量带来的影响。论文的主要工作如下:①概述了基于瑞利散射的振动传感技术及基于拉曼散射的温度传感技术的相关理论,为实现两种技术的结合奠定了理论知识。首先通过建立后向瑞利散射的离散模型描述了φ-OTDR系统的基本原理,而后从量子力学的角度阐释了ROTDR系统的测温原理,并对常用的温度解调方法进行了介绍。讨论了系统的各参数指标对整体设计的要求,并在此基础上分析了分布式振动及温度传感系统的可行性。②对多参数分布式光纤传感系统的关键技术及主要器件进行了实验研究。通过对不同脉冲参数下得到的振动及温度测量结果进行分析,认为高功率的脉冲光可以获得高信噪比的自发拉曼散射信号,但同时会产生非线性效应导致振动测量难以实现,如若降低探测脉冲光功率则会较大地影响系统的测温精度。因此,认为采用合适的调制脉冲方式对于实现振动及温度的同时测量和提高系统性能是及其关键的。③为了实现分布式光纤振动及温度的同时测量,利用声光调制器连续产生的高、低功率的探测光脉冲,并通过高功率的脉冲光产生的拉曼散射进行温度解调,通过低功率的脉冲光产生的瑞利散射进行振动解调。在1.2km的传感光纤上实现了空间分辨率为5.8m,振动频率为1k Hz及10k Hz的振动测量,同时还实现了空间分辨率为4.8m,测温精度约±3℃的温度测量。④对于实验中所采用的脉冲调制方式,将会影响振动测量的频率响应范围。由于振动是快速变化的动态信号,而温度则是一个缓变的信号,因而文章提出一种改进的脉冲调制方法,以减小温度探测脉冲的重复频率为代价来增大振动探测脉冲的重复频率,这样既能使振动测量的频响范围不受影响,同时也能满足温度测量的要求。通过实验研究表明,利用脉冲调制的方式,可有效避免非线性效应带来的影响并同时提高系统的信噪比,从而实现结合瑞利散射及拉曼散射的多参数分布式传感系统。该系统结构简单且成本较低,进一步提高系统性能将在未来的实际应用中发挥出更大的作用及价值。
[Abstract]:The distributed optical fiber sensing technology uses the optical fiber itself as a signal transmission medium and as a sensing unit, thus obtaining the distribution of the external physical quantity along the whole fiber path. The distributed optical fiber sensing system has high measurement precision, long sensing distance and good reliability. It has been widely used in long distance infrastructure. However, the occurrence of a fault is usually shown as a strain or a vibration event, or a change in a variety of parameters, such as the change of the ambient temperature. Only the monitoring of a single physical quantity can not ensure an effective early warning and location for the accident. Therefore, the distributed measurement of multiple parameters is becoming more and more important and gradually distributed. At present, the distributed measurement of multi parameters is mainly focused on the simultaneous measurement of stress and temperature at home and abroad. The principle is to make use of the temperature effect of Raman scattering and the variation of Brillouin frequency shift with the variation of strain and temperature. The OTDR system of Rayleigh scattering and spontaneous Raman scattering realizes the distributed measurement of vibration and temperature. The Raman scattering signal with high signal to noise ratio is obtained by pulse modulation, and the influence of nonlinear generation is avoided. The main work of this paper is as follows: (1) the vibration sensing technology and base based on Rayleigh scattering are described. The theory of temperature sensing technology of Raman scattering has laid a theoretical knowledge for the realization of the combination of the two technologies. Firstly, the basic principle of the -OTDR system is described by the discrete model of the backward Rayleigh scattering, then the temperature measurement principle of the ROTDR system is explained from the angle of quantum mechanics, and the commonly used temperature demodulation methods are carried out. The requirements for the overall design of the parameters of the system are discussed, and the feasibility of the distributed vibration and temperature sensing system is analyzed on this basis. 2. The key technologies and main components of the multi parameter distributed optical fiber sensing system are experimentally studied. The vibration and temperature measurements obtained under different pulse parameters are measured. The result is that the high power pulse light can obtain the spontaneous Raman scattering signal with high signal to noise ratio, but the nonlinear effect causes the vibration measurement to be difficult to be realized. If the detection pulse light power is reduced, the temperature measurement precision will be greatly affected. Therefore, it is considered that the appropriate modulation pulse mode is used to realize the vibration. To measure and improve the performance of the system at the same time and temperature is the key. (3) in order to realize the simultaneous measurement of distributed optical fiber vibration and temperature, the high, low power detection optical pulse generated by the acoustooptic modulator is used continuously, and the temperature is demodulated by the Raman scattering produced by high power pulse light, and the low power pulse light is produced. The vibration demodulation is carried out by Rayleigh scattering. The spatial resolution of 1.2km is 5.8m, the vibration frequency is 1K Hz and 10K Hz, and the spatial resolution is 4.8m, and the temperature measurement accuracy is about 3 C. 4. The pulse pulse modulation method used in the experiment will affect the frequency of vibration measurement. The response range. Because the vibration is a fast changing dynamic signal and the temperature is a slow change signal, a modified pulse modulation method is proposed to increase the repetition frequency of the vibration detection pulse at the cost of reducing the repetition rate of the temperature detection pulse, so that the frequency response range of the vibration measurement is not affected. It can also meet the requirements of temperature measurement. Through the experimental study, it is shown that the influence of the nonlinear effect can be avoided and the signal to noise ratio of the system can be improved by pulse modulation, and the multi parameter distributed sensing system combining Rayleigh scattering and Raman scattering is realized. The system is simple in structure and low in cost, and is further proposed. High system performance will play a greater role and value in future practical applications.

【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN253

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