Simulation of distributed optical fiber disturbance detection system based on Sagnac/Mach-Zehnder interferometer and cross-correlation location

A distributed optical fiber disturbance detection system consisted of a Sagnac interferometer and a Mach-Zehnder interferometer is demonstrated. Two interferometers outputs are connected to an electric band-pass filter via a detector respectively. The central frequencies of the two filters are selected adaptively according to the disturbance frequency. The disturbance frequency is obtained by either frequency spectrum of the two interferometers outputs. An alarm is given out only when the Sagnac interferometer output is changed. A disturbance position is determined by calculating a time difference with a cross-correlation method between the filter output connected to the Sagnac interferometer and derivative of the filter output connected to the Mach-Zehnder interferometer. The frequency spectrum, derivative and cross-correlation are obtained by a signal processing system. Theory analysis and simulation results are presented. They show that the system structure and location method are effective, accurate, and immune to environmental variations.

Practical Pattern Recognition System for Distributed Optical Fiber Intrusion Monitoring Based on Ф-COTDR

At present, the demand for perimeter security system is in-creasing greatly, especially for such system based on distribut-ed optical fiber sensing. This paper proposes a perimeter se-curity monitoring system based on phase-sensitive coherentoptical time domain reflectometry(Ф-COTDR) with the practi-cal pattern recognition function. We use fast Fourier trans-form(FFT) to exact features from intrusion events and a multi-class classification algorithm derived from support vector ma-chine(SVM) to work as a pattern recognition technique. Fivedifferent types of events are classified by using a classifica-tion algorithm based on SVM through a three-dimensional fea-ture vector. Moreover, the identification results of the patternrecognition system show that an identification accurate rate of92.62% on average can be achieved.

An all optical fiber gas sensor of NH3 and CO based on based on the spectral absorption and harmonic detection

An all optical fiber gas sensor is presented to detect the concentration of NH3 and CO. Based on the spectral absorption, The wideband light source is used to reflect two narrowband spectra by fiber grating of different duty. and piezoelectric ceramics to obtain narrowband output light. The high sensitivity detection can be measured from the second harmonic signal. The two narrowband spectra are corresponding to the absorption spectra of NH3 and CO. Concentration detection are realized by the detection of variety of light intensity. Sensitivity is proved and cost is reduced.

Simulation Tools for a Fiber-Optic Based Structural Health Monitoring System

Probability of detection(POD)graphics allow for a change from qualitative to quantitative assessment for every damage detection system,and as such it is a main request for conventional non-destructive testing(NDT)techniques.Its availability can greatly help towards the industrialization of the corresponding Structural health monitoring(SHM)system.But having in mind that for SHM systems the sensors are at fixed positions,and the location of a potential damage would change its detectability.Consequently robust simulation tools are required to obtain the model assisted probability of detection(MAPOD)which is needed to validate the SHM system.This tool may also help for the optimization of the sensor distribution,and finally will allow a probabilistic risk management.INDEUS,simulation of ultrasonic waves SHM system,was a main milestone in this direction.This article deals with the simulation tools for a strain based SHM system,using fiber optic sensors(FOS).FOS are essentially strain/temperature sensors,either with multi-point or with distributed sensing.The simulation tool includes the finite element model(FEM)for the original and damaged structure,and algorithms to compare the strain data at the pre-established sensors locations,and from this comparison to extract information about damage occurrence and location.The study has been applied to the structure of an all-composite unmanned aircraft vehicle(UAV)now under construction,designed at Universidad Politecnica de Madrid for the inspection of electrical utilities networks.Distributed sensing optical fibers were internally bonded at the fuselage and wing.Routine inspection is planned to be done with the aircraft at the test bench by imposing known loads.From the acquired strain data,damage occurrence may be calculated as slight deviations from the baselines.This is a fast inspection procedure without requiring trained specialists,and it would allow for detection of hidden damages.Simulation indicates that stringer partial debondings are detected before they become critical,while small delaminations as those produced by barely visible impact damages would require a prohibited number of sensing lines.These simulation tools may easily be applied to any other complex structure,just by changing the FEM models.From these results it is shown how a fiber optic based SHM system may be used as a reliable damage detection procedure.

Feature Extraction and Identification in Distributed Optical-Fiber Vibration Sensing System for Oil Pipeline Safety Monitoring

High sensitivity of a distributed optical-fiber vibration sensing （DOVS） system based on the phase-sensitivity optical time domain reflectometry （Ф-OTDR） technology also brings in high nuisance alarm rates （NARs） in real applications. In this paper, feature extraction methods of wavelet decomposition （WD） and wavelet packet decomposition （WPD） are comparatively studied for three typical field testing signals, and an artificial neural network （ANN） is built for the event identification. The comparison results prove that the WPD performs a little better than the WD for the DOVS signal analysis and identification in oil pipeline safety monitoring. The identification rate can be improved up to 94.4%, and the nuisance alarm rate can be effectively controlled as low as 5.6% for the identification network with the wavelet packet energy distribution features.

Application of Golay codes to distributed optical fiber sensor for long-distance oil pipeline leakage and external damage detection

A new distributed optical fiber sensor system for long-distance oil pipeline leakage and external damage detection is presented. A smart and sensitive optical fiber cable is buried beneath the soil running along the oil pipeline, which is sensitive to soakage of oil products and mechanical deformation and vibration caused by leaking, tampering, and mechanical impacting. The region of additional attenuation can be located based on the optical time domain reflectometry （OTDR）, and the types of external disturbances can be identified according to the characteristics of transmitted optical power. The Golay codes are utilized to improve the range-resolution performance of the OTDR sub-system and offer a method to characterize the transmitted optical power in a wide range of frequency spectrum. Theoretic analysis and simulation experiment have shown that the application of Golay codes can overcome the shortcomings of the prototype based on the conventional single-pulse OTDR.

A Two-Level Detection Algorithm for Optical Fiber Vibration

Optical fiber vibration is detected by the coherent optical time domain reflection technique. In addition to the vibration signals, the reflected signals include clutters and noises, which lead to a high false alarm rate. The ＂cell averaging＂ constant false alarm rate algorithm has a high computing speed, but its detection performance will be declined in nonhomogeneous environments such as multiple targets. The ＂order statistics＂ constant false alarm rate algorithm has a distinct advantage in multiple target environments, but it has a lower computing speed. An intelligent two-level detection algorithm is presented based on ＂cell averaging＂ constant false alarm rate and ＂order statistics＂ constant false alarm rate which work in serial way, and the detection speed of ＂cell averaging＂ constant false alarm rate and performance of ＂order statistics＂ constant false alarm rate are conserved, respectively. Through the adaptive selection, the ＂cell averaging＂ is applied in homogeneous environments, and the two-level detection algorithm is employed in nonhomogeneous environments. Our Monte Carlo simulation results demonstrate that considering different signal noise ratios, the proposed algorithm gives better detection probability than that of ＂order statistics＂.

Technology of fiber-optic temperature sensing and its application in ＆ temperature measuring of gob area

Based on advantages of technology of distributive fiber-optic temperature sensing and specific to its applications in monitoring mine conflagration, the corresponding Processes such as connection arrangement, signal transmission and monitoring were illustrated. As applied in Sitai Coal Mine of Datong Coal Mine Group Co., this method is effective and accurate and could provide reliable gist for monitoring spontaneous combustion in gob area of mines.

Life cycle detection of prestress in large prestressed reinforcement structures

To monitor the stress state of prestressed reinforcement in large reinforcement prestressed structure, two sensing structures, namely the direct spiral-winding structure and sawtooth modulated structure, were designed based on the ordinary communication optical fiber. The sensing theories were analyzed, and the experimental studies were also carried out. The quasi-distributed sensing system based on optical time domain reflective technology was established. The detection wavelength and spatial resolution were analyzed, and the estimation formula of maximal number of sensing point was also given. The results show that the system can realize the quasi-distributed test of measurand with single fiber, which helps to simplify the in-out wires. Moreover it can take on the important task of long-term and continuous monitoring of prestress, which helps to realize the life cycle detection of prestress, and play an important role in the estimating of bridge health state.

预应力混凝土梁腐蚀断丝水下监测试验研究

采用人工通电加速腐蚀的方法模拟混凝土梁内预应力钢筋的自然断裂过程从而获得真实的断丝声发射信号,应用高频声发射传感器和分布式光纤监测系统从水下采集预应力钢筋断裂时产生的声信号,分析信号的时频域特征和时域统计特征参数,结果表明:断丝信号的超声波段在水中传播时发生频散,应采用20 kHz以下的时域统计特征识别断丝信号;铠装光缆可以接收到在水中传播的断丝信号,其在时频图上表现为一条竖直的条带,并且能量主要集中分布于100~200 Hz。采用时域统计特征参数分析光纤监测信号时,需要设定较小的门槛值截取信号进行分析;对于光纤水声监测工况来说,峰值指标的信噪比较低,裕度和峭度指标更适合于用来识别断丝信号。该研究为开发预应力混凝土结构断丝水下声光纤监测系统奠定了基础。

光纤传感技术在油气田开发中的应用

分布式光纤监测技术在油气田开发中具有无可比拟的优势。从分布式光纤传感技术基本原理和井中布设方式出发,介绍了光纤传感技术在水力压裂、连续油管产液剖面测试、邻井压裂监测、油气井注采监测、储气库安全监测和套损监测等多个石油工程领域应用情况。整体表明光纤监测是一种经济高效的监测技术,具备实时监控油气井全生命周期的潜力,是具有科学性、时代特性和安全高效的生产测井技术。同时指出分布式光纤传感技术在油田应用的未来发展应聚焦于提升传感器性能、丰富光纤监测场景应用、提高资料处理解释水平能力,降低应用成本,进一步发挥光纤在油气田开发中的作用。

基于SOA光纤环形激光器的分布式声传感系统

为了降低传统分布式声学传感器(DAS)系统复杂度并提高信噪比(SNR),提出了一种基于半导体光放大器的光纤环形激光器(SOA-FRL)的DAS系统。该系统用SOA-FRL取代了传统的DAS系统中的窄线宽激光器和脉冲调制器,实现了高稳定的光脉冲输出;采用双脉冲外差探测方法,实现了精确的声信号探测和声源定位。实验结果表明:在频率为1 kHz、幅值为1.14 rad的声信号作用下,所提系统的解调SNR高达38.25 dB,空间分辨率为12 m。

基于振动提取的沙漠埋地管道弯曲变形监测技术研究

针对在沙漠环境中的流动性沙丘区域服役的埋地管道,易产生变形的问题,提出一种基于振动信号的变形监测技术。首先分析沙漠环境中埋地管道变形特性,建立沙漠埋地管道有限元模型;然后基于有限元分析软件(ANSYS)进行弯曲管道流固耦合作用下的模态分析;最后通过分布式光纤传感技术,采集管道弯曲变形处的异常振动信号。研究结果表明:沙丘移位导致埋地管道产生弯曲变形时,内部流体会在弯曲变形处与管体发生耦合作用导致该处产生异常振动,通过分布式光纤传感技术采集该异常信号能够实现振动监测,结合特征提取与支持向量机可以实现管道变形监测。

基于有限元仿真和光纤传感的隧道损伤监测

对苏州四号线支线红庄站至蠡墅站段地铁进行隧道结构开展静力场和动力场有限元仿真分析,并根据仿真结果和现场勘察结果,成功设计并布设了能够对隧道结构水平位移、裂缝、沉降、结构应力、结构表面应变、振动等信息进行实时监测的光纤传感网络,实现了对隧道结构健康状态的实时监测,然后利用光纤传感网络反过来验证有限元模型可靠性,从而得到更准确的有限元仿真模型。最后,结合两种技术,针对该地铁中三种主要断面建立了二维有限元模型,研究了三种断面在隧道结构有损伤基础和无损伤基础的两种情况下,受到地铁列车振动荷载影响产生的混凝土结构损伤分布规律,从而更好地为地铁安全运营提供技术保障。

基于直线型Sagnac的光纤周界安防系统设计

变电站安防系统的建设对保证整个电力系统安全运行有着重要作用,为了推进变电站无人值守化的进程,提高电力系统供电的可靠性,设计了一种基于直线型Sagnac的光纤周界安防系统,并对光纤振动信号的检测方法进行了详细论证,提出了基于多域特征的动态阈值端点检测算法,从时域、频域和小波域提取振动信号的特征进行判断,实时更新特征阈值,通过三级判定算法提高系统对入侵事件的检测效果.将光纤安防系统与视屏监控系统、微信报警系统和声光报警系统结合,可对无人值守的变电站进行全天候、多技术手段融合的立体防护.

分布式光纤声学检测技术在煤矿带式输送机监测中的应用

带式输送机是现代化的输送设备,具有高效、节能、环保的特性。利用光纤声学检测技术,研究了基于分布式光纤声波检测技术的带式输送机健康监测原理、系统架构、托辊定位、光纤部署方式、轴承中滚珠开裂的监测等技术,将高速行进的输送带和托辊摩擦碰撞的声音作为声发射源,使用基于机器学习的声纹识别技术,实时地、全天候地监测带式输送机并提供健康监测的预警服务。研究引入光纤声学检测,来实现带式输送机的健康监测应用,具有非常重要的战略意义。

利用PLC、触摸屏和多轴运动设计智能机器人

为适应市场竞争各企业必须花大成本对企业内部进行改造,在欧美发达国家应用较为成熟自动化设备技术前题下,是国内企业可学习和借鉴的好办法。特别是对大型陶瓷插芯注塑机塑件的拣取、检测、加工、分放系统改造,实现全自动生产,可提高生产效率和产品质量、降低成本和减少安全事故发生。本文通过PLC、触摸屏、伺服电机、3轴运动以及其它非标设备进行组合设计,实现完整的陶瓷插芯注塑机塑件的拣取、检测、加工、分放机器人系统,使该机器人与注塑机结合使用,提高生产效率和改善产品品质。通过采集注塑机的相关信号,并将该机器人系统与注塑机实际联机调试,发现配合完整、运行稳定、效率高。实践证明,陶瓷插芯注塑机塑件拣取、检测、加工、分放机器人系统能使每台注塑机24小时减少3名操作工人,效率提高了53%,塑件质量提高了3.8%,运行1年无人员安全事故发生。

基于分布式光纤声波传感技术的管道泄漏探测应用

文章介绍了分布式光纤声波传感(distributed fiber optic acoustic sensing,DAS)技术的工作原理及其在管道泄漏检测中的应用。DAS系统通过光纤中背向瑞利散射光的变化来检测光纤上沿途感知到的声波信息,再结合光时域反射技术获取外部扰动事件所处的位置,从而通过检测和分析背向散射的光信号,提取外界扰动对应的位置和相位。文章搭建了一套试验系统,通过试验检测了DAS运用于管道泄漏探测的可靠性。试验表明,DAS技术可以检测并识别不同位置和类型的泄漏事件。为了进一步提高泄漏检测效果,文章设计了一种分析方法,通过数据预处理、特征提取、事件检测和泄漏识别与分类,实现了对泄漏事件的精准识别和定位,并提高了其在泄漏检测中的灵敏度和实时性。该方法结合DAS的技术特点,可以在长距离和大范围内提供高效、可靠的泄漏监测。

面向DVS振动信号识别率提升的特征选择算法研究

分布式光纤振动传感(Distributed Optic-fiber Vibration Sensing, DVS)系统可对振动信号实现分布式测量,在实际应用中通常采用模式识别算法对各种振动事件进行识别,然而目前模式识别特征大都固定冗余,不能充分展现振动信号的特性,导致误报率高的问题。针对上述问题,搭建了一套直接探测结构的DVS系统样机,并提出了基于模拟退火算法和Fisher Score算法相结合的混合式特征选择方法。首先使用Fisher Score算法选取合适的特征初始集合,再将Fisher Score嵌入模拟退火算法的新解产生环节中,实现对入侵振动信号的特征组合整体效果较好的选择。通过实验对算法性能进行验证,结果表明:该算法可以剔除冗余入侵振动信号特征,拥有较快的收敛速度,使系统的识别率由80.23%提升至94.46%。

基于光纤传感技术的变压器高温区域典型热源定位

针对油浸式变压器温度检测及热点跟踪方面存在精度低的问题,提出了一种基于分布式光纤传感(DFOS)技术的变压器高温区域检测框架。设计了油浸式变压器绕组上的光纤布设方案,从而为实时获取变压器内部热点数据奠定基础。通过实验测试,所设计的DFOS变压器可有效检测热源,并对热点进行跟踪与定位。所设计的光纤布设方案能够保持变压器正常运行的稳定状态,并与变压器油具有良好的兼容性。对4个变压器热点模型与DFPS数据的均方根误差(RMSE)值进行分析,证明Susa模型为描述变压器动态热行为的最佳模型。