Lift-Off Effect of Koch and Circular Differential Pickup Eddy Current Probes

A flexible or planar eddy current probe with a differential structure can suppress the lift-off noise during the inspection of defects.However,the extent of the lift-off effect on differential probes,including different coil structures,varies.In this study,two planar eddy current probes with differential pickup structures and the same size,Koch and circular probes,were used to compare lift-off effects.The eddy current distributions of the probes perturbed by 0°and 90°cracks were obtained by finite element analysis.The analysis results show that the 90°crack can impede the eddy current induced by the Koch probe even further at relatively low lift-off distance.The peak-to-peak values of the signal output from the two probes were compared at different lift-off distances using finite element analysis and experimental methods.In addition,the effects of different frequencies on the lift-off were studied experimentally.The results show that the signal peak-to-peak value of the Koch probe for the inspection of cracks in 90°orientation is larger than that of the circular probe when the lift-off distance is smaller than 1.2 mm.In addition,the influence of the lift-off distance on the peak-to-peak signal value of the two probes was studied via normalization.This indicates that the influence becomes more evident with an increase in excitation frequency.This research discloses the lift-off effect of differential planar eddy current probes with different coil shapes and proves the detection merit of the Koch probe for 90°cracks at low lift-off distances.

Study of Current Sheath Velocity and Its Distribution Using Tridimensional Magnetic Probe in Sahand Plasma Focus

The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 （cm/μs） and 3.92 ± 0.75 （cm/μs） with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 （cm/μs） at the radial phase and 1.14 ± 0.09 （cm/μs） at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum （FWHM） of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.

脉冲涡流缺陷检测理论与技术研究综述

由于具有非接触、效率高、检测信号的信息含量丰富等诸多优点,脉冲涡流技术被广泛应用工业产品的缺陷检测,尤其是带包覆层、异质、以及多层导电结构等检测难度极大的工业产品。脉冲涡流探头结构的设计和优化是提高检测灵敏度和准确度的关键,目前大量的研究工作围绕探头结构的设计和优化开展;不同材质、结构、以及缺陷类型或形状需要选用合适特征量表征,特征量的选取与分析也是脉冲涡流技术研究的关键;另外,由于脉冲涡流检测信号受提离高度影响极大,未知提离高度的缺陷准确检测面临极大的挑战,因此提离效应的抑制也是研究的重点之一。本文从探头的设计与开发、特征量的选取与分析、提离效应的抑制等方面,对脉冲涡流检测技术的研究进展进行综述。同时,为更好的推动脉冲涡流检测技术发展,论文在现有的研究基础上,对脉冲涡流探头设计、特征量分析、以及提离效应抑制等进行了展望。

基于直流电位降法的缺陷区域多探针检测

油气管道在服役过程中由于制造过程、环境复杂等因素容易产生缺陷,造成管道破裂等事故,因此对管道的无损检测具有重要意义。通过直流电位降法研究裂纹缺陷对电位场的影响规律,建立了多探针缺陷检测方法。首先采用有限元法对含有缺陷的平板试样进行电位分析,缺陷区域的电位差明显高于无缺陷区域,通过多探针的检测范围对试样区域进行划分后,提出了多探针缺陷区域检测方法。检测到区域存在缺陷后,对缺陷影响因子k进行计算,无缺陷区域k值基本在0.8~1.2之间,而缺陷周围的k值都超过了2,根据k值的分布可以得到缺陷的大致位置和尺寸。并搭建了多探针检测试验平台进行试验,结果表明,缺陷附近的电势差显著高于其他区域,与有限元结果相符。缺陷区域电势差明显高于其他区域,无缺陷区域k值在0.75~1.2之间,缺陷区域k值基本大于1.5。通过k值分布对缺陷位置和尺寸进行分析,与实际尺寸相差在3~5 mm左右。

基于COMSOL仿真软件的电涡流传感器教学探索

为了提升课堂教学效果,辅助学生理解电涡流传感器的检测原理及相关抽象概念,采用COMSOL仿真软件,构建了电涡流传感器探头线圈的仿真模型,并采用有限元的分析方法对其进行求解计算。通过对仿真结果的分析,学生可以直观地看到,当涡流线圈激励频率、提离距离、线圈内径、线圈外径和线圈厚度变化时,电涡流传感器的检测灵敏度将随之发生变化,有助于学生对电涡流传感器相关知识的理解和掌握,提高了学生的学习热情和思考深度。

预混火焰离子/电子电流区域性差异研究

研究预混火焰不同区域离子电流与电子电流分布对分析火焰燃烧状态具有重要作用.在探针测量预混火焰的实验中,发现了预混火焰不同区域两种电流分布存在差异.为了进一步对离子电流与电子电流产生差异的原因进行分析,基于FLUENT通过数值模拟仿真得到了影响电流的因素——正负极性带电粒子及其迁移率的分布,并在此基础上结合电离反应机理、带电粒子性质以及火焰流场速度对带电粒子的分布进行了解释.研究发现,由于电子迁移率远大于其他带电粒子,导致预混火焰整体区域的电子电流高于离子电流,其中,中性物质的分布是影响电子迁移率最重要的因素.电子电流与离子电流的差值随着与本生灯距离的增加表现为类似“M”状变化趋势,并在预混火焰反应区附近出现了极小值.不同极性带电粒子在火焰中的分布存在差异,该差异反映了化学反应、对流和带电粒子自身性质等多种因素的共同作用,其中,电子与正离子均在反应区产生,导致正离子集中存在于反应区,而电子由于具有极小的质量,导致其扩散到火焰的其他区域,负离子分布在中性物质与电子共同存在的区域.由于火焰中不同极性带电粒子分布存在差异,因此火焰的局部区域可能表现出单一的电极性,这为基于静电感应原理的火焰非接触式电学测量提供了可能.

不同类型涡流探头对蒸汽发生器传热管缺陷检测能力的对比分析

为研究不同类型涡流探头对蒸汽发生器传热管缺陷的检测能力,分别采用轴绕式探头、旋转探头与阵列探头,对位于自由段的孔形、槽形、磨损缺陷和疲劳裂纹进行试验、对胀管过渡区孔形和槽形缺陷进行试验,还进行了缺陷分辨力试验,发现旋转探头与阵列探头具有相近的缺陷检出能力,对于间距较小的缺陷和胀管过渡段上的缺陷等复合缺陷,旋转探头与阵列探头的缺陷检出能力均明显优于轴绕式探头的。

The Effect of Ion Current Density on Target Etching in Radio Frequency-Magnetron Sputtering Process

The effect of ion current density of argon plasma on target sputtering in magnetron sputtering process was investigated. Using home-made ion probe with computer-based data acquisition system, the ion current density as functions of discharge power, gas pressure and positions was measured. A double-hump shape was found in ion current density curve after the analysis of the effects of power and pressure. The data demonstrate that ion current density increases with the increase in gas pressure in spite of slightly at the double-hump site, sharply at wave-trough and side positions. Simultaneously, the ion current density increases upon increase in power. Es- pecially, the ion current density steeply increases at the double-hump site. The highest energy of the secondary electrons arising from Larmor precession was found at the double-hump position, which results in high ion density. The target was etched seriously at the double-hump position due to the high ion density there. The data indicates that the increase in power can lead to a high sputtering speed rate.

基于电流探头法的环天线校准系统研究

为解决电磁兼容检测领域环天线溯源的问题,根据电流探头法的校准原理,利用数字电磁学代码(NEC)建模分析了环天线校准系统的关键影响因素,推导了校准系统的天线系数计算公式。在3米法半电波暗室建立了基于电流探头法的环天线校准系统,并校准了辐射骚扰试验常用的两款环天线,校准结果与标称值最大误差为0.56 dB,且在天线系数的最大允差范围内,验证了环天线校准系统的可信性和精确性。为表征校准结果的区间半宽度,根据推导的天线系数计算公式,阐述了标准不确定度分量的评定过程,校准系统的扩展不确定度为1.3 dB(k=2)。

实验室传导发射电磁环境噪声超标案例分析

试验场地传导发射电流法环境噪声测试时出现了尖峰毛刺、鼓包等骚扰信号。根据排查流程,从被试品的辐射和传导耦合路径入手进行分析,显示器电源适配器使用滤波器组插排时,测试数据正常,骚扰源定位在显示器电源适配器。进一步验证发现,不接滤波器组插排,分别更换为笔记本电脑适配器、ViewSonic显示器,也能消除骚扰信号。问题的分析思路、分析方法可供试验室人员解决类似试验场地电磁环境噪声问题时参考。

碳钢件焊缝缺陷检测用正交涡流探头研究

由于传统涡流探头具有明显的提离效应,难以检测表面不平整的焊缝。为此,基于均匀涡流检测原理,设计一种用于焊缝缺陷检测的正交涡流探头。采用理论计算方法,研究正交探头检测原理,设计探头有限元仿真模型,分析探头结构和线圈尺寸对检测灵敏度的影响。利用设计的正交涡流探头对碳钢件焊缝开展探伤检测试验。当提离量不大于2 mm时,有效检测出宽度为0.25 mm、深度为1 mm的碳钢板焊缝表面人工开口裂纹。试验结果表明,正交涡流探头能有效抑制检测过程中提离效应的影响,验证了探头用于焊缝表面缺陷检测的可行性。

直流电弧等离子体炬数值模拟与诊断

直流电弧等离子体炬内部物理过程复杂且具动态性,较难对其进行准确描述与深入研究,且其工作温度较高,其状态参数难以使用常规方式测量。针对直流电弧等离子体炬,建立流动、传热和电磁相互耦合的数值模型,基于Fluent软件对直流电弧等离子体炬进行三维数值模拟和特性分析,设计并搭建了一套热焓探针实验系统,完成对直流电弧等离子体炬射流参数的测量分析。结果表明:建立的数值模型模拟结果与实验测量结果吻合较好,误差在10%以内;炬内温度与速度最大值与工作气流量呈正相关,均出现在靠近阴极区域,且沿轴线逐渐降低;等离子体炬内高温区与高电流密度区重合。

应用于涡流无损检测的柔性磁阻传感器

为了研究平面探头和曲面探头在检测平面缺陷和曲面缺陷方面的差异,本文分别使用刚性印刷电路板和柔性印刷电路板(FPC)设计了刚性探头和柔性探头。实验结果表明,在平面铝板上,刚性探头和柔性探头的信噪比分别为30.2 dB和24.6 dB。在弯曲缺陷中,刚性探头的信噪比最低为14.8 dB,柔性探头的信噪比最低为27.1 dB。综合考虑温度稳定性、信噪比、价格等因素,刚性探头适用于小曲率的平面缺陷检测,柔性探头适用于曲面检测。

涡流X-probe探头的试验及应用

探头是阵列涡流检测的关键部件,介绍了一种新型的内穿过式涡流阵列探头——X-probe。分析了X-probe探头的工作原理,并通过试验研究,归纳了X-probe探头检测的不同类型缺陷信号特征、支撑下缺陷响应以及伤深与相位的关系。并介绍了X-probe探头在核电厂凝汽器传热管涡流检查的应用情况。试验结果表明,X-probe探头能够获取缺陷轮廓并依据AF和CF通道的幅值分辨出缺陷方向。现场应用证实X-probe探头具有良好的管板区缺陷检出能力,能很好地检测分辨并测量周向复合缺陷的伤深。

基于刀片式激励线圈旋转的脉冲涡流探头

脉冲涡流检测裂纹时,微裂纹在感应涡流中产生的扰动微弱,检测信号的信噪比低;另一方面,单向扫查下的常规脉冲涡流探头难以获得多向裂纹检测的最大灵敏度和判断裂纹方向。提出一种采用机电旋转脉冲涡流激励线圈的检测方法,实现了多方向微裂纹的高灵敏度检测。刀片式激励线圈具有明显的聚磁性与方向性,机电旋转激励线圈后可以获得不同转角下的接收信号,将该接收信号与基准信号进行差分,提取出微小的峰值变化量,得到角度与峰值变化量之间的图谱。试验验证与测试结果表明:基于刀片式激励线圈在空心接收线圈内旋转的脉冲涡流探头不仅具有亚毫米级裂纹深度区分的检测能力,且能有效分辨裂纹方向,误差为±5°。

以钢丝绳为例的无损检测——磁化涡流爬壁机器人

设计一种磁化涡流波无损检测爬壁机器人,基于磁化涡流技术和阵列涡流技术的仿真实践,设计并制造出多通路、高精度的MBF滤波互感式探头。仿真结果表明,探头对信号处理和特征提取算法的实际性应用可行性高,并用可调频率BMF滤波器对信号干扰的处理,通过波特图和磁场分布图的对比进行钢丝绳缺陷的判断处理,使无损检测的效率、精准度提高且减少传统的人力、物力资源的浪费。

基于交流电磁场的支管角焊缝表面缺陷检测系统

基于交流电磁场检测(ACFM)技术,开发了一套支管角焊缝表面缺陷检测系统。设计了包含ACFM探头和便携式机箱的硬件检测系统,针对检测信号的特点开发了信号平滑滤波算法,提高了信号的信噪比,并基于LabVIEW平台编写了集信号采集、信号处理和信号显示为一体的检测软件,最后形成一套完整的交流电磁场支管角焊缝表面缺陷检测系统,并采用该系统对Q345材料角焊缝试件进行检测。试验结果表明,所设计的交流电磁场缺陷检测系统能实现支管角焊缝表面缺陷信号的有效降噪和准确识别。

ARRAY PULSED EDDY CURRENT IMAGING SYSTEM USED TO DETECT CORROSION

A theory model is established to describe the voltage-current responsefunction. The peak amplitude and the zero-crossing time of the transient signal is extracted as theimaging features, array pulsed eddy current (PEC) imaging is proposed to detect corrosion. The testresults show that this system has the advantage of fast scanning speed, different imaging mode andquantitative detection, it has a broad application in the aviation nondestructive testing.

The Langmuir Probe onboard CSES: data inversion analysis method and first results

The Langmuir Probe(LAP), onboard the China Seismo-Electromagnetic Satellite(CSES), has been designed for in situ measurements of bulk parameters of the ionosphere plasma, the first Chinese application of in-situ measurement technology in the field of space exploration. The two main parameters measured by LAP are electron density and temperature. In this paper, a brief description of the LAP and its work mode are provided. Based on characteristics of the LAP, and assuming an ideal plasma environment, we introduce in detail a method used to invert the I-V curve; the data products that can be accessed by users are shown. Based on the LAP data available, this paper reports that events such as earthquakes and magnetic storms are preceded and followed by obvious abnormal changes. We suggest that LAP could provide a valuable data set for studies of space weather, seismic events, and the ionospheric environment.

Automatic emissive probe apparatus for accurate plasma and vacuum space potential measurements

We have developed an automatic emissive probe apparatus based on the improved inflection point method of the emissive probe for accurate measurements of both plasma potential and vacuum space potential.The apparatus consists of a computer controlled data acquisition card,a working circuit composed by a biasing unit and a heating unit,as well as an emissive probe.With the set parameters of the probe scanning bias,the probe heating current and the fitting range,the apparatus can automatically execute the improved inflection point method and give the measured result.The validity of the automatic emissive probe apparatus is demonstrated in a test measurement of vacuum potential distribution between two parallel plates,showing an excellent accuracy of 0.1 V.Plasma potential was also measured,exhibiting high efficiency and convenient use of the apparatus for space potential measurements.