【作者】 钟峰；

【导师】 宋文爱；

【作者基本信息】 中北大学 ， 信号与信息处理， 2009， 硕士

【摘要】 噪声是影响超声在线检测系统性能的一个重要因素,对超声采集信号信噪比的高低有直接影响。本文对药柱超声在线检测系统的噪声问题从理论分析和工程实践两个方面进行了研究,旨在解决超声在线检测系统中的噪声干扰问题,从而提高系统性能和采集信号的信噪比。超声在线自动检测系统包括PLC控制系统、超声换能器、发射接收电路、数据采集卡和工控机。影响超声在线检测系统的噪声与其系统组成是密不可分的。在超声在线检测系统中影响最大的噪声来源于PLC控制系统的伺服电机和变频电机,也就是电磁兼容噪声。超声在线检测系统的噪声还包括换能器与换能器屏蔽电缆线的阻抗匹配噪声以及超声探伤仪本身所产生的噪声。本文在研究电磁兼容噪声和系统固有噪声来源的基础上,针对各自特点分别采用不同的处理方法进行去噪处理。首先,对电磁兼容噪声,在理论分析和工程实践的基础上,提出了电源隔离、超声探头架和检测水槽采用胶木或尼龙等绝缘材料制作,取得了较好的降噪效果;其次,从信号处理的角度出发,分别采用传统的滤波方法和小波变换方式对所采集的信号进行了进一步的降噪处理,为后续的超声信号缺陷识别算法的实现奠定了基础,为固体火箭发动机药柱实现线性定量超声检测提供了条件。对提高固体火箭发动机药柱超声在线系统的可靠性和稳定性具有较大的实际参考价值。更多还原

【Abstract】 Noise, an important factor which impact on the performance of ultrasonic online testing system, has a direct influence on the signal-to-noise ratio’s level of ultrasonic signal acquisition. Noise problem of grain ultrasonic online testing system has been studied in this paper from two aspects, theoretical analysis and engineering practices. In this case, we can solve the noise interference problem in ultrasonic online testing system, and improve the performance of system and signal-to-noise ratio of signal acquisition.Ultrasonic online automatic testing system includes PLC control system, ultrasonic transducer, transceiver circuits, data acquisition card and industrial computer. The noise which influences the ultrasonic online testing system is inseparable with its system composition. In ultrasonic online testing system, the noise which has great effect on the system, also named as electromagnetic compatibility noise is derived from servo motor and variable-frequency motor of the PLC control system. The noise in the ultrasonic online testing system includes the impedance matching noise of transducer and its screened cable, as well as the one produced by ultrasonic defect detector itself.In this paper, the research has been based on the sources of electromagnetic compatibility noise and inherent system noise. The author uses different treatment approaches on denoising separately in view of the respective characteristic. First of all, based on the theoretical analysis and the engineering practices, the author puts forward several ideas on electromagnetic compatibility noise, such as the isolation of power supply, the set of ultrasonic probes, and detecting-sink which is made of insulation material, e.g. bakelite or nylon, and achieves good results in noise reduction. Next, in the view of signal processing, the acquisitied signals have been processed by the traditional filtering method and the wavelet transform respectively for further noise reduction processing. All the studies above lay the foundation for the realization of follow-up ultrasonic signal defect recognition algorithm, and provide conditions for the realization of linear quantitative ultrasonic testing of solid-propellant rocket engine grain. It shows a greater value in the improvement of ultrasonic online system’s reliability and stability of solid-propellant rocket engine grain更多还原