| Railway is important infrastructure of a nation. By the end of 2005, the overall length of China's railway has reached 75 thousand kilometers. Consequently, the number of flawed rails has also been increasing rapidly—totaled 250,000 for the year 2001, which imposed great potential danger on railway security. Current analog detectors, due to their low accuracy and speed, are not able to meet the requirements of rail test. Thanks to the rapid development of digital technology, novel digital ultrasonic detector is becoming the main method of rail test.In this paper, a new solution to the problems existed in current rail detectors, is proposed based on comprehensive references and thorough analysis. DSP&CPLD- centered digital signal processing technique is applied in rail ultrasonic detector, thus developing a novel digital detector. Based on the traditional type, new components, such as signal analyzing & processing module, signal storage module, display & alert module, etc are added, which results in improvement in the instrument's performance and decrease in errors.The main achievements include:(1) Based on the technique of A-type ultrasonic pulse echo flaw testing instrument, the DSP&CPLD-centered digital rail ultrasonic detector, including its software part and hardware part, is designed.(2) To solve the existing problems, such as low sampling rate and inconstant display, CPLD is employed to compress data. Circuit of each unit and Verilog HDL source code are presented. Simulate timing sequence is analyzed as well.(3) Display module, which consists of QVSM01 LCD controller, MCU and dual-port RAM, is designed.(4) Basic functions of the ultrasonic detector are tested. Outcomes and errors are analyzed.
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