【作者】 于亚婷；

【导师】 杜平安；

【作者基本信息】 电子科技大学 ， 机械电子工程， 2007， 博士

【摘要】 为消除被测材料电磁特性对电涡流传感器输出的影响、提高传感器的灵敏度和线性范围,本文以电涡流传感器基本理论、时谐电磁场理论和有限元建模理论为基础,研究了被测材料电磁特性和传感器线圈阻抗之间的关系,提出通过矢量投影方法和幅值/相位混合调制思想消除被测材料电磁特性对传感器输出的影响;同时研究了探头结构及其几何参数与线圈阻抗的关系,从而得出探头结构及其几何参数和线圈阻抗的关系,并以此指导探头结构的优化设计。本文主要对以下几个方面进行了深入研究:1.线圈阻抗理论计算方法的研究根据研究需要建立了磁性/非磁性被测体下线圈阻抗的理论求解模型,从理论上推导了磁性被测体下线圈的阻抗积分表达式,在利用贝赛尔级数将阻抗积分表达式展开成级数表达式后利用Mathematic^TM得到了线圈阻抗值。2.线圈阻抗数值计算方法研究根据电涡流传感器的几何特征和边界条件,结合有限元建模理论,建立了电涡流传感器的2D和3D数值计算模型,根据电磁场时谐分析结果得到了线圈阻抗值的数值计算方法,并获得线圈阻抗值。3.与被测材料无关的电涡流传感器基础理论研究提出同时获取线圈电阻和感抗两个信号,通过矢量投影法消除被测材料电磁特性对传感器输出的影响;采用有限元法和试验法验证了提出的方法的正确性和可行性;根据验证结论提出了对传感器进行非线性校正的方法。4.与被测材料无关的电涡流传感器功能电路的设计与仿真在验证的基础上,根据提出的消除被测材料电磁特性对传感器输出影响的方法和非线性校正方法,采用幅值/相位混合调制的设计思想,利用Multisim对功能电路进行设计与仿真。5.功能电路的功能测试试验研究根据电路设计的特点和关键器件的性能特征,在protel DXP中进行布局和布线;制板和元器件焊接后对PCB电路进行调试。利用调试好的电路板搭建了实验平台并对电路功能进行了测试。6.探头线圈结构及其几何参数对传感器性能影响研究通过理论推导和有限元法从线圈形状及其几何参数和铁氧体磁芯及其几何参数两个角度研究了探头线圈结构及其几何参数对传感器阻抗与检测距离的关系曲线的影响。以上研究不仅消除了被测材料电磁特性对传感器输出的影响,而且对线圈阻抗的研究也从非磁性被测体发展到磁性被测体;从线圈阻抗的角度探索探头结构及其几何参数对传感器性能的影响,使研究结果对探头结构的优化更具指导意义。本文的创新点概括如下:1.建立了磁性/非磁性被测体下传感器线圈阻抗的统一计算模型电涡流传感器测量中被测量的变化通过线圈阻抗的变化来体现,因此线圈阻抗是传感器测量中的重要物理量。而目前关于线圈阻抗的研究主要针对非磁性被测体,对磁性被测体下线圈阻抗计算方法的研究较少。文中建立了磁性/非磁性被测体下传感器线圈阻抗的统一计算数学模型和有限元分析模型。通过数学模型详细推导了磁性/非磁性被测体下线圈阻抗的积分表达式,并针对线圈阻抗积分表达式的特点,提出采用贝塞尔级数展开并截取空气边界的方法获取线圈阻抗的理论计算值;通过有限元分析模型得到了传感器的磁场分布、被测体中的涡流分布和线圈阻抗值。该项研究使关于线圈阻抗计算方法的研究从非磁性被测体向磁性被测体拓展,进一步完善了涡流检测理论。2.提出消除被测体电磁特性对传感器输出影响的方法根据磁场能量守恒定理和对不同电磁特性被测体对传感器输出影响的研究,得出在相同检测距离、不同被测体下线圈电阻和感抗之间存在线性关系,据此提出采用矢量投影法消除传感器测量中被测体电磁特性影响的方法;通过试验法和有限元仿真方法验证了该方法的可行性和正确性;最后通过线圈阻抗幅值/相位混合调制思想实现了传感器输出和被测材料无关的功能。3.通过线圈阻抗研究探头结构及其几何参数和传感器性能之间的关系在被测参数一定的情况下,线圈阻抗变化不仅直接体现了探头结构及其参数的变化,而且阻抗变化趋势也体现了传感器性能的好坏。目前关于这方面的研究主要是通过探头结构及线圈参数对传感器的磁场分布的影响进行,而关于线圈磁场分布的理论推导存在大量假设,实验测量较困难且仪器昂贵,测量不便。与此相比,线圈阻抗的计算和测量更为方便和准确。因此提出通过线圈阻抗确定探头结构及其几何参数对传感器性能的影响关系。更多还原

【Abstract】 Aimed at eliminating the influence of the electromagnetic properties of measured material on the output voltage of eddy current sensor and improving the sensor’s performances, this thesis focuses on studying the relationship between the electromagnetic properties of measured material and the coil impedance; presents the approach that the coil impedance vectors are projected onto the projection plane and the amplitude/phase mixed modulation approach to eliminate the influence of the electromagnetic properties of measured material on the output voltage of eddy current sensor. In addition, this thesis also researches the influences of the probe structure and its geometric parameters on the coil impedance, which are helpful to optimize the probe and improve the sensor’s performances.To sum up, the following works are carried out:1. Research on the theoretical computational method to the coil impedanceThe theoretical computational model of eddy current sensor with the non-magneticand magnetic measured material is constructed, the coil impedance integral expression is deduced, and the coil impedance value is obtained by the Bessel series expansion using software package Mathematic?.2. Research on the numerical computation method to the coil impedanceBased on the geometric characteristics and boundary conditions of eddy currentsensor, 2D and 3D finite element models of eddy current sensor are built, respectively. The coil current is obtained by the time-harmonic electromagnetic analysis, and the coil impedance value is got according to the coil current obtained before.3. Fundamental theory for material-independent eddy current sensorThe approach that the coil impedance vectors are projected onto the projection plane is presented to eliminate the influence of the electromagnetic properties of measured material on the output voltage of eddy current sensor by extracting two signals: coil resistance signal and inductance signal; the effectivity and feasibility of the approach above is validated by finite element method and experiment method. Meanwhile, the nonlinear errors compensation approaches are presented according to the validated conclusions.4. The functional circuit design and simulation of material-independent eddy current sensorAccording to the validation conclusions and the presented approach eliminating the influence of the electromagnetic properties of measured material on the output voltage of eddy current sensor, the amplitude/phase mixed modulation approach are adopted to design, the designed circuit is simulated in software package Multisim, and the functional circuit and the fitting function method is used to compensate the nonlinear errors.5. The experiment on the functional circuitBased on the characteristics of designed circuit and the properties of key components, the layout and wiring of PCB is performed in software package Protel DXP; The circuit is debugged after the components are welded; The experiment platform is constructed and the function of the circuit is experimented.6. Research on the influence of the probe structures and its geometric parameters on the sensor’s performancesThe influences of the probe structure and its geometric parameters on the coil impedance are investigated in terms of coil shape and its geometric parameters, the ferrite core and its geometric parameters by the theoretical deduction and finite element method. The influences of them on the sensor’s performances are determined further.The researches above can eliminate the influence of the electromagnetic properties of measured material on the output voltage of eddy current sensor, as well as result in that the study on coil impedance from the nonmagnetic measured material to the magnetic one, that the conclusions on the influence of the probe structure and its geometric parameters arrived from the coil impedance is more effective to instruct the design of probe than those from the magnetic flux distribution.The originalities in this thesis can be summarized as follows:1. The computational models of coil impedance under a magnetic and nonmagnetic measured material are builtThe measurand of eddy current testing is embodied by the change of coil impedance. Therefore, the coil impedance is a very important physical quantity in eddy current testing. However, the present studies mainly focus on the nonmagnetic measured material, and the researches on the coil impedance under the magnetic one are limited. The mathematical model of coil impedance and finite element model under a magnetic and nonmagnetic measured material are built, respectively. Based on the mathematical model, the integral expression of coil impedance under the magnetic and nonmagnetic measured material is deduced in detail. To obtain the coil impedance value conveniently, the integral expression of coil impedance is expanded as the Bessel series and the air domain is truncated, and the impedance value is obtained by Mathematic^TM. Based on the finite element model, the magnetic flux distribution of sensor, the eddy current distribution in measured and the coil impedance value are computed, respectively. The above research develops the research on the coil impedance computational methods from the nonmagnetic measured material to the magnetic one, which promotes the eddy current testing theory perfect.2. The approach to eliminate the influence of the electromagnetic properties of measured material on the output voltage of sensor is presented.According to the energy conservation principle and the conclusions arrived from the analysis to the change of coil impedance under different measured material, the phenomenon that the coil resistance and inductance under different materials and the same measurement distance is linear is discovered. Therefore, the approach that the coil impedance vectors are projected onto the projection plane is put forward to eliminate the influence of the electromagnetic properties of measured material on the output voltage of sensor, and finite element method and experiment method validate the above approach is feasible and effective. Finally, the amplitude/phase mixed modulation approach is used to design the functional circuit.3. The relationships between the probe structure, geometric parameters and the sensor’s performances are investigated in terms of coil impedance.When the measurand is constant, the changes of the probe structure and its geometric parameters not only show the changes of coil impedance, but also affect the sensor’s performances. The present studies mainly pay attention to the influence of the probe structure and its geometric parameters on the electromagnetic field distribution of eddy current sensor. However, there are many hypotheses in the theoretical deduction about the electromagnetic field distribution, it is difficult and inaccurate to measure the electromagnetic field distribution. In addition, the instrument measuring the electromagnetic field distribution is expansive. Compared with the electromagnetic field distribution, the computation and measurement to the coil impedance is more accurate and convenient. Hence, the conclusions arrived from the influences of the probe structure and its geometric parameters on the sensor’s performances are more effective to instruct the design of probe and improve the sensor’s performances.更多还原