Acoustic Emission Testing (AT) is one of the major non-destructive testing methods used for severity evaluation of structures. Amplitude distributions of AE signals are characterized by b-value and the value is mainly...Acoustic Emission Testing (AT) is one of the major non-destructive testing methods used for severity evaluation of structures. Amplitude distributions of AE signals are characterized by b-value and the value is mainly used for the severity evaluation of concrete structures until now. The value is assumed to be independent with propagation distance between acoustic emission sources to AE sensors. We evaluate the influence of the wide frequency band encountered in the fracture behavior of glass fiber reinforced plastic (GFRP) on the b-value analysis. In tensile tests, the b-value was determined from an acoustic emission (AE) source generated near a centered hole in a specimen of GFRP. At 15 mm from the hole, the b-value analysis indicated a decreasing trend with increasing tensile stress. At a propagation length of 45 mm, farthest from the hole, a?small number of AE signals were received. The attenuation is more rapid for high-frequency AE signals. Thus, the amplitude distribution bandwidth is wide and the b-value changes. This change in b-value for GFRPs is investigated by analyzing the spectral components of the AE signals. For a single-frequency AE source, the b-value is unchanged with propagation length. In contrast, multiple-frequency AE sources produce changes in b-value proportional to the fraction of each spectral component in the received signal. This is due to the frequency dependence of the attenuation with propagation length.?From these results, the b-value analysis cannot be applied to considering frequency dependence of AE attenuation.展开更多
设计了逐位比较型数字通信误码测试系统.首先,分析了误码测试系统的基本架构及其各组成功能模块;其次,讨论了误码测试系统中各关键模块的实现方法;最后,利用Quartus II 7.2软件平台对设计的数字误码测试系统进行了仿真分析,验证了设计...设计了逐位比较型数字通信误码测试系统.首先,分析了误码测试系统的基本架构及其各组成功能模块;其次,讨论了误码测试系统中各关键模块的实现方法;最后,利用Quartus II 7.2软件平台对设计的数字误码测试系统进行了仿真分析,验证了设计的正确性.展开更多
针对通信系统解调损失测试过程中存在的引用理论误码率不准确以及保证置信度情况下的码元测试长度的标准不一问题,对部分常引用错误的调制体制的理论误码率进行了推导分析,对误码率测试长度与置信度之间的关系进行分析计算,得到在置信度...针对通信系统解调损失测试过程中存在的引用理论误码率不准确以及保证置信度情况下的码元测试长度的标准不一问题,对部分常引用错误的调制体制的理论误码率进行了推导分析,对误码率测试长度与置信度之间的关系进行分析计算,得到在置信度0.99情况下码元测试长度应不小于136/Pe(Pe为系统的误码率上限)。开展了验证实验,实验数据表明,错误的引用BPSK以及CPFSK(非相干解调)的理论误码率将引起解调损失误差分别不小于0.7 d B和1.0 d B;相对于136/Pe的码元测试长度下的解调损失的重复性为0.08 d B,10/Pe的码元测试长度下的解调损失的重复性增大了4倍。展开更多
光纤复合相导线(Optical Phase Conductor,OPPC)在电网节能和抗冰灾方面有其优越性,但传统的OPPC技术繁琐复杂,给施工带来了不便。广东电网公司于2009年开发了新型OPPC光单元分离引下技术,并在10 k V配电线路中投入应用,适合110 k V架...光纤复合相导线(Optical Phase Conductor,OPPC)在电网节能和抗冰灾方面有其优越性,但传统的OPPC技术繁琐复杂,给施工带来了不便。广东电网公司于2009年开发了新型OPPC光单元分离引下技术,并在10 k V配电线路中投入应用,适合110 k V架空输电线路的全绝缘光单元OPPC技术也已于近期开发成功,文章对110 k V线路OPPC全绝缘光单元直接引下试验及其应用进行了介绍。在此背景下,OPPC架空送电线路建设可望摆脱繁琐的传统技术,为电力通信光纤线路建设提供一种较好的选择。展开更多
文摘Acoustic Emission Testing (AT) is one of the major non-destructive testing methods used for severity evaluation of structures. Amplitude distributions of AE signals are characterized by b-value and the value is mainly used for the severity evaluation of concrete structures until now. The value is assumed to be independent with propagation distance between acoustic emission sources to AE sensors. We evaluate the influence of the wide frequency band encountered in the fracture behavior of glass fiber reinforced plastic (GFRP) on the b-value analysis. In tensile tests, the b-value was determined from an acoustic emission (AE) source generated near a centered hole in a specimen of GFRP. At 15 mm from the hole, the b-value analysis indicated a decreasing trend with increasing tensile stress. At a propagation length of 45 mm, farthest from the hole, a?small number of AE signals were received. The attenuation is more rapid for high-frequency AE signals. Thus, the amplitude distribution bandwidth is wide and the b-value changes. This change in b-value for GFRPs is investigated by analyzing the spectral components of the AE signals. For a single-frequency AE source, the b-value is unchanged with propagation length. In contrast, multiple-frequency AE sources produce changes in b-value proportional to the fraction of each spectral component in the received signal. This is due to the frequency dependence of the attenuation with propagation length.?From these results, the b-value analysis cannot be applied to considering frequency dependence of AE attenuation.
文摘针对通信系统解调损失测试过程中存在的引用理论误码率不准确以及保证置信度情况下的码元测试长度的标准不一问题,对部分常引用错误的调制体制的理论误码率进行了推导分析,对误码率测试长度与置信度之间的关系进行分析计算,得到在置信度0.99情况下码元测试长度应不小于136/Pe(Pe为系统的误码率上限)。开展了验证实验,实验数据表明,错误的引用BPSK以及CPFSK(非相干解调)的理论误码率将引起解调损失误差分别不小于0.7 d B和1.0 d B;相对于136/Pe的码元测试长度下的解调损失的重复性为0.08 d B,10/Pe的码元测试长度下的解调损失的重复性增大了4倍。
文摘光纤复合相导线(Optical Phase Conductor,OPPC)在电网节能和抗冰灾方面有其优越性,但传统的OPPC技术繁琐复杂,给施工带来了不便。广东电网公司于2009年开发了新型OPPC光单元分离引下技术,并在10 k V配电线路中投入应用,适合110 k V架空输电线路的全绝缘光单元OPPC技术也已于近期开发成功,文章对110 k V线路OPPC全绝缘光单元直接引下试验及其应用进行了介绍。在此背景下,OPPC架空送电线路建设可望摆脱繁琐的传统技术,为电力通信光纤线路建设提供一种较好的选择。
