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How to use distributed fiber optic temperature measurement system in urban rail transit

The comprehensive application of fiber optic technology and the detection of rail transit vehicles can help fundamentally improve the performance of rail vehicles. In recent years, research on the safety technology of rail transit vehicles has gradually deepened both domestically and internationally, with more emphasis on preventive alarms before vehicle failures and real-time monitoring technology for vehicle operation. Fiber optic technology, due to its inherent advantages, has been widely applied in many fields. The application of fiber optic technology in foreign countries is relatively mature, but in China, the research on the application of fiber optic technology in rail vehicles still needs further improvement.

1、 Application of Distributed Fiber Optic Temperature Measurement System in Urban Rail Transit
The application of distributed fiber optic temperature measurement system in urban rail transit mainly relies on the principles of light scattering and optical time-domain radiation. This distributed fiber optic temperature measurement system has high measurement accuracy and can shield the interference of strong electromagnetic fields. Moreover, with the optimization of temperature rise algorithms, intelligent demodulation technology, and signal optimization technology, the application scope of distributed fiber optic temperature measurement system will be further expanded to meet the operational needs of urban rail transit vehicles, and timely alarm for existing fire hazards. At present, the common principle of distributed fiber optic temperature measurement technology is mainly based on Raman scattering. After modulation, the scattered light enters the wavelength division multiplexer to obtain Stokes light and anti Stokes light. The relative sensitivity of Stokes light to temperature is 0.104%, and the relative sensitivity of anti Stokes light to temperature is 1.065%. The ratio of light intensity is 4:3. Based on the characteristics of Stokes light and anti Stokes light, a quantitative relationship between light intensity ratio and temperature can be obtained. On this basis, combined with the internal reference temperature of the temperature measurement system and corresponding correction algorithms, the actual temperature information can be obtained. With the rapid development of distributed fiber optic temperature sensing technology, the application scope of this measurement system is gradually expanding, especially in the application of urban rail transit. Even in the face of more complex internal systems and large traffic passenger flow, it can accurately carry out monitoring, effectively eliminate fire hazards, and meet the operational needs of urban rail transit.

2、 Application of redundant fiber optic ring network in urban rail transit power monitoring system
The application of redundant fiber optic ring network in urban rail transit power monitoring system mainly utilizes the characteristics of urban rail transit power monitoring system to monitor the power supply equipment of substations passing along the rail vehicle line, in order to ensure the stable operation of the rail transit power system and the normal operation of rail transit vehicles. The power monitoring system in urban rail transit mainly includes three parts: station control layer, interval layer, and network layer. The station control layer can also be divided into communication controllers, computers, and human-machine interfaces. The network layer includes switches, fiber optic transceivers, optical cables, and other lines to provide communication channels for the power monitoring system. Therefore, it can be seen that the current rail vehicle transportation power monitoring system adopts a layered structure, but with the development of national network equipment and network technology, the network structure of the rail vehicle transportation power monitoring system has also undergone significant changes. From single bus star structure and Ethernet star structure to redundant fiber optic ring network, the power monitoring system of rail vehicle transportation has gradually improved. As a network structure in the new era of rail vehicle transportation power monitoring system, redundant fiber optic ring network plays a crucial role in solving redundancy problems in the network layer. With the development of redundant fiber optic ring network, redundant fiber optic ring network optical switches have emerged. Therefore, redundant fiber optic ring network has been used in power monitoring systems. To fully utilize the role of redundant fiber optic ring networks in power monitoring systems, it is necessary to conduct in-depth research on the structure and communication of redundant fiber optic ring networks. Taking the power monitoring system of rail transit in a certain area as an example, rail transit personnel in the area want to use a redundant fiber optic ring network. Firstly, appropriate ring network nodes are set up, and then according to the specific rail transit substation, 35kV and 400V switchgear, DC 1500V switchgear, and regenerative braking devices are installed. Among them, the rail transit lines 3 and 5 in C city have adopted redundant fiber optic ring networks to monitor the power system, effectively improving the redundancy interoperability of the monitoring system network.

3、 Application of Fiber Bragg Grating Sensing Technology in Rail Transit Vehicles
Firstly, a brief understanding of the application principles of fiber optic grating sensing technology and its technological advantages in rail transit vehicles was provided. Fiber Bragg Grating sensing technology mainly applies FBG sensors to monitor rail transit vehicles. The specific principle is as follows: with the changes in physical quantities such as temperature, strain, displacement, and acceleration around the fiber Bragg grating, the period and refractive index of the fiber Bragg grating will also change, resulting in wavelength displacement of the Bragg grating signal. FBG sensors monitor the changes in Bragg wavelength displacement to determine the changes in physical quantities in the surrounding environment of the fiber Bragg grating. Simultaneously, wavelength division multiplexing technology is used to form a fiber optic grating sensing system, achieving high-capacity distributed measurement. At the same time, this fiber optic grating sensing system can also achieve remote real-time monitoring. Taking the fiber optic grating sensing system as an example for detecting the health status of wheel axles, when a rail vehicle passes through the steel rail next to the sensor, it will cause a change in Bragg wavelength displacement. After passing through the FBG sensor, a strain curve will be formed, and the corresponding wheel axle book will be obtained. By analyzing the actual situation of the strain curve, the health status of the wheel axle can be judged, and wheel defects can be effectively and timely detected. The most crucial sensor sword in fiber optic grating sensing systems is the FBG sensor. Among them, the FBG sensor produced by MOI Company in the United States can achieve a scanning frequency of 2kHz and a measurement accuracy of 1 με, The optical performance is extremely stable. The fiber optic grating sensing system has high measurement accuracy, fast scanning speed, low complexity, high resolution, and a large coverage range.

In summary, based on different principles of fiber optic technology and utilizing the characteristics of fiber optic technology, this article describes the application of fiber optic technology in rail vehicles from multiple aspects. At present, the application of fiber optic technology in urban rail vehicles has not been fully promoted, far less than the number of infrastructure inspection projects. However, looking at the development of urban rail vehicles, it is necessary to use fiber optic technology to ensure the safety and stability of urban rail vehicle transportation. Moreover, the application of fiber optic technology in urban rail vehicle transportation has great market demand prospects.

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