涡流检测多层平板导体参数的频率选择方法

涡流检测多层平板导体参数具有重要意义,其中激励频率的选择是关键。针对正弦涡流法检测多层平板导体厚度与电导率问题,以被测导体上方空心圆柱线圈散射场电感为测量量,提出通过求解灵敏度函数选择激励频率的方法。对于检测线圈尺寸参数已知、被测多层平板导体参数可估计的情况,利用灵敏度函数曲线可以得到任意被测参数检测灵敏度最大值及所对应的频率,在各参数灵敏度函数最大值所对应的频率附近分别选取3～4个频率点,实现激励频率的选择。最后进行三层平板导体厚度与电导率检测实验,在相同的频率区间内,分别利用灵敏度函数选频法和平均选频法对散射场电感扫频测量结果进行频率选择,实验结果显示前者各参数检测误差普遍小于后者,验证了灵敏度函数选频法的有效性。

A Frequency Selection Method for Parameter Measurement of the Metallic Multi-layer Plate Using Eddy Current

Parameter measurement of the metallic multi-layer plate is of great significance and the frequency selection is the key. With respect to this problem, the eddy current inductance of the air-core cylindrical coil above the metallic multi-layer plate was measured and a frequency selection method was proposed using the sensitivity function of the coil eddy current inductance. When the coil parameters were known and the metallic multi-layer plate parameters could be estimated, both the maximum sensitivity and the corresponding frequency of each parameter were obtained using the sensitivity function curve. Then, 3-4 frequency points were chosen in the vicinity of the frequency corresponding to the maximum value of the sensitivity function of each parameter. Finally, the thickness and conductivity measurement for a metallic three-layer plate was conducted. In the same frequency range, the frequency selection method based on the sensitivity function and the average frequency selection were both utilized to choose the frequency points from the measurement values of the eddy current inductance. The results show that the measurement errors of the former method are mostly smaller than ones of the latter, which verifies the effectiveness of the frequency selection method using the sensitivity function.