Meng Xiaobai, Lu Mingyang, Yin Wuliang, Bennecer Abdeldjalil, Kirk Katherine J
Faculty of Art, Science and Technology, University of Northampton, Northampton NN1 5PH, UK.
School of Electrical and Electronic Engineering, University of Manchester, Sackville Street Building, Manchester M13 9PL, UK.
Sensors (Basel). 2021 Jan 9;21(2):419. doi: 10.3390/s21020419.
Defect detection in ferromagnetic substrates is often hampered by nonmagnetic coating thickness variation when using conventional eddy current testing technique. The lift-off distance between the sample and the sensor is one of the main obstacles for the thickness measurement of nonmagnetic coatings on ferromagnetic substrates when using the eddy current testing technique. Based on the eddy current thin-skin effect and the lift-off insensitive inductance (LII), a simplified iterative algorithm is proposed for reducing the lift-off variation effect using a multifrequency sensor. Compared to the previous techniques on compensating the lift-off error (e.g., the lift-off point of intersection) while retrieving the thickness, the simplified inductance algorithms avoid the computation burden of integration, which are used as embedded algorithms for the online retrieval of lift-offs via each frequency channel. The LII is determined by the dimension and geometry of the sensor, thus eliminating the need for empirical calibration. The method is validated by means of experimental measurements of the inductance of coatings with different materials and thicknesses on ferrous substrates (dual-phase alloy). The error of the calculated coating thickness has been controlled to within 3% for an extended lift-off range of up to 10 mm.
当使用传统的涡流检测技术时，铁磁基体中的缺陷检测常常受到非磁性涂层厚度变化的阻碍。在使用涡流检测技术时，样品与传感器之间的提离距离是测量铁磁基体上非磁性涂层厚度的主要障碍之一。基于涡流趋肤效应和提离不敏感电感（LII），提出了一种简化的迭代算法，用于使用多频传感器减少提离变化的影响。与以往在获取厚度时补偿提离误差（如提离交点）的技术相比，简化的电感算法避免了积分的计算负担，这些算法被用作通过每个频率通道在线获取提离的嵌入式算法。LII由传感器的尺寸和几何形状决定，因此无需进行经验校准。通过对铁基体（双相合金）上不同材料和厚度涂层的电感进行实验测量，验证了该方法的有效性。在高达10mm的扩展提离范围内，计算出的涂层厚度误差已控制在3%以内。
