The Development Of Portable Track Frequency Shift Signal Detection Instrument

From the period of “11th five-year plan” proposed to accelerate the development of railway and urban transportation planning, China has gradually entered the era of “high-speed rail", the emergence of the high-speed rail speed up the flow speed of passenger and freight, the overall efficiency of railway transportation was improved, make a new contribution to China’s economic development and social progress. But the speed and gradually increasing train density of high-speed train also put forward higher requirements for the railway sector to train control and operation.Track circuit is a very important part in the railway transportation system, shoulder the task of train operation control and information transmission, FSK signal is a "language" between the railway electricity section and locomotive in the track circuit, FSK signal can not only reflect the location of the train, but also detect the running speed of the locomotive, transmit control signals to the locomotive. Therefore, develop a detection instrument which can detect the characteristic parameters of FSK signal quickly and accurately to meet the high-speed railway, detect of equipment failure timely, maintain of frequency shift equipment stability, ensure the safe operation of the train, has important practical significance.In this paper, we focused on the frequency shift current signal of ZPW-2000 A type track circuit used in domestic railway passenger transport commonly as the research object, through reading a large number of relevant technical documents and site investigation, designed a overall program of portable frequency shift signal detector, designed the instrument hardware circuit and software program, through field and laboratory experiments proved that the design instrument meets the track shift frequency signal detection requirements. Main research contents of this article are as follows:According to the Rules of railway signal maintenance and actual needs of the railway sector to a portable frequency shift instrument, we established the qualification and design scheme of the detection instrument; proposed the FSK current detection method based on magneto resistance effect, through the analysis on the performance of magneto resistive sensor and simulation of magnetic field distribution of peripheral tracks, the mapping relationship between the output voltage of the magnetic resistance sensor and the external magnetic field of the railway is summarized, the result demonstrates the feasibility of the method.Detailing the expression of FSK signals and interference sources,thorough analysis and research of the signals in the time domain and frequency domain characteristics, proposed the FSK signal demodulation algorithm based on band-pass sampling technology and FFT, simulated the demodulation algorithm by using Matlab, the results show that this algorithm can demodulate frequency shift signal frequency parameter accurately and the resolution ratio reached 0.01 Hz.With stability, reliability of the premise, high energy, miniaturization, energy as the design concept, using C6748 DSP as the core, designed the instrumentation hardware circuit, including microcontroller peripheral circuit, the sensing unit circuit, automatic range selection circuit, AD converting circuit, WIFI communication circuits, power circuit, LCD screen interface circuit, reset circuit.The software flow of the detector is designed, and the procedures of each function module is compiled under the CCS5.5 development environment, include: data acquisition program, FIR filtering procedures, FFT algorithm procedures, frequency parameter calculation procedures, RMS procedures, WIFI communication procedures, display procedures, etc.Functional verification test and performance test are carried out in the laboratory and in the field, including sensor output linearity verification experiment, sensor temperature characteristic verification experiment, set and reset output verification experiment, sensing element immunity performance field test, track frequency shift signal detection performance test, voltage and current detection performance test, WIFI communication performance test. Verification experiment and performance test results showed that the design of instrumentation can detect the frequency shift signal characteristic parameters stably, accurately, efficiently and conveniently, prepared the ground for the development of portable frequency shift detecting.