Research And Design On Defects Detection System For Natural Gas Pipeline

Over the years, the explosion caused by the natural gas pipeline leak has increased yearby year, which is due to the following reasons：prolonged use of the pipeline, imperfectpipeline maintenance，delay pipe wall defects found. Therefore, it is meaningful to doresearch on gas pipeline wall defect detection.With the rapid development of the ultrasonic detection theory,the disciplines of digitalsignal processing technology and automated with intelligent technology, it is proved thatusing ultrasonic testing technology for pipeline detection has a fast speed, high efficiency andaccurate results, no environmental pollution and small cost. Therefore the application range isvery wide. Based on gas pipeline as the research object, this paper applies the pulse reflectionmethod to detect pipeline defects, uses DSP chip as the core of the digital signal processingtechnology applied to ultrasonic testing system and the SD card to store data.This article is aimed at the inner wall of the gas pipeline defect recognition. Firstly, thepaper completes the design of robot body structure, including the drive speed controlstructure, the arrangement of the ultrasonic probe as well as the safety of the design; Secondly,through the analysis of the theory and technology of ultrasonic detection, the overall designof the ultrasonic testing system is proposed based on a digital signal processor (DSP), Thehardware design of the system includes limiting the protection of the signal in the ultrasonictransmitting circuit and a receiving circuit, amplification, filter design; the design of DSPapplication system includes power supply design, clock and reset circuit, battery selectionand memory SD card interface circuit design. The software design of the system includes theinitialization of DSP system, the software implementations of A/D signal conversion, andthe SD memory card reads and writes in SPI mode, and creates a file system on the SDmemory card to manage document operation.Ultrasonic echo signal is a kind of time-varying signal, not only contains many usefulinformation, but also mingled with a lot of noise,. It is common to use wavelet thresholddenoising method to reduce noise, but denoising capacity of different threshold functionshave different effects. After analysis of hard and soft threshold function, a new thresholdfunction is constructed, which can avoid loss of useful information after treated by the softthreshold function, as well as avoid the additional oscillation after treated by the hard threshold function.A suitable mother wavelet function is determined by simulation of several commonmother wavelet function, as well as combined with the characteristics of the ultrasonic echosignal. In denoising experiments, the paper applies the actual use of soft and hard thresholdfunction and the improved threshold function to ultrasonic echo signal. Validated byexperimental results, improved threshold function has the very good denoising ability, andalso has a good denoising effect in a low signal-to-noise ratio.