| In China, as an infrastructure, railway system plays an important role in the development of the national economy. At the same time, the public began to pay more attention to the safety of railway operation. Balise Transmission Module (BTM) is an important component of the Automatic Train Protection (ATP) system. During its operation, BTM will always be exposed to electromagnetic interference that may cause the system faulted or degraded. Therefore, it will be very helpful to monitor and record the noise level of the BTM’s receive signal in order to do interference troubleshooting and fault diagnosis. Currently, there is no dedicated online monitoring equipment to complete the real-time dynamic monitoring and recording for the BTM’s wireless link. In this thesis, a portable recorder is designed to complete real-time online monitoring and recording of the electromagnetic environment around BTM.In this thesis, the system components and working principle of BTM is analyzed based on the domestic and overseas researches. The main technical indicator is concluded as references to make system design. Then the communication frequency is analyzed to design a reasonable signal extraction device of radio link. The system dynamic range is expanded by using a logarithmic amplifier with appropriate performance. A customized embedded ARM-Linux is used as the core of the system. Reliable power supply for each part of the system is provided by the train DC power and an independed Li-on bettery sub-system. What’s more, an aluminum chassis is admitted to ensure good EMC characteristics.The design of signal extraction module is based on active analog filter circuits that constructed of the integrated operational amplifiers. Two stage of4order Butterworth low-pass filters with cut-off frequency of7MHz are used which can provide-60dB suppression to27MHz downlink signal. Furthermore, a cascade Inverse Chebyshev band-pass filter is used for the monitoring band, which can ensure good rectangle coefficient and flatness of filter’s passband. Then a buffer amplifier is used after the filters to make impedance matching to prevent signal reflection. A logarithmic amplification circuit is used to achieve the signal compression and expansion to widen the dynamic range of monitoring, as well as to achieve the dynamic matching with the input voltage range of A/D conversion module.In the central control system module, the embedded ARM-Linux system is used. By loading the Bootloader, the operating system is booted and configurated. The root file system, the hardware drivers, and the writing of programs in system application control layer are developed. The system achieves a series of functions, such as the corresponding to the sleep/wake action, task scheduling, power supply management, data collection and storage, and so on.The EMC design of the system involves various levels, including component-level, circuit-level and system-level considerations. Such as components choosing, modularizational PCB layout, power supply&signal traces routing and decoupling, grounding plane pouring, power supply conversion and filtering, and aluminum chassis designing, series details have been taken into account to ensure electromagnetic compatibility of the system.The system of BTM electromagnetic interference recorder designed in this thesis can be used to replaces the original coupling device and generic instruments (such as spectrum analyzers and oscilloscopes) in the traditional BTM signal test solutions, and can save much manual operation. As an online record, the system can store signals and noises in digital form, as well as automatically sleep or wake according to the operation of the train. The electromagnetic environment levels will be monitored and recorded in real time during the whole process of train’s driving. What’s more, by working with the playback and analysis software, the recorded data can provide powerful help to BTM interference analysis and troubleshooting. |
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