电涡流传感器中变压器型等效电路的适用性研究

Study on applicability of transformer equivalent circuit in eddy current non-destructive evaluation

为考察电涡流传感器中等效电路的适用性,本文从被测体材料角度出发,在分析等效电路基础上,采用分离变量法和数值计算法,得到不同被测材料下探头线圈阻抗与提离高度的关系,并与从等效电路得出的结论比较,确定等效电路的适用性,同时考察被测体厚度对线圈阻抗的影响,最后对得出的结论进行理论分析。结果表明,等效电路的适用性与被测体的涡流渗透厚度无关;对非磁性材料作用下的检测系统,等效电路适用,对铁磁性材料则不适用;同时在计算线圈阻抗时,应保证被测体厚度大于其涡流渗透厚度的20%。

In this paper, the study on the applicability of the equivalent circuit in eddy current sensor is performed. Firstly, the equivalent circuit is analyzed in details. Secondly, the relationship between the coil impedance and its liftoff for different materials are obtained using separation of variables and numerical calculation methods. Comparing with the results from equivalent circuit, the applicability of the equivalent circuit can be determined. Moreover, the influence of the thickness of the measured material on the coil impedance is also investigated. Finally, the conclusion is analyzed theoretically. Through study and analysis, the following conclusion is derived： the applicability of the equivalent circuit is not related to the penetration thickness of measured material; the equivalent circuit is applicable for non-magnetic material, and it is not applicable for ferromagnetic material. Furthermore, due to the influence of skin effect, the coil impedance is calculated accurately only when the thickness of measured material is greater than 20% of its penetration thickness.