Liu Ze, Koffman Andrew D, Waltrip Bryan C, Wang Yicheng
Beijing Jiaotong University, Beijing, P.R. China , 100044 ; National Institute of Standards and Technology, Gaithersburg, MD 20899.
National Institute of Standards and Technology, Gaithersburg, MD 20899.
J Res Natl Inst Stand Technol. 2013 Feb 26;118:140-9. doi: 10.6028/jres.118.007. eCollection 2013.
AC bridge techniques commonly used for precision impedance measurements have been adapted to develop an eddy current sensor for rail defect detection. By using two detection coils instead of just one as in a conventional sensor, we can balance out the large baseline signals corresponding to a normal rail. We have significantly enhanced the detection sensitivity of the eddy current method by detecting and demodulating the differential signal of the two coils induced by rail defects, using a digital lock-in amplifier algorithm. We have also explored compensating for the lift-off effect of the eddy current sensor due to vibrations by using the summing signal of the detection coils to measure the lift-off distance. The dominant component of the summing signal is a constant resulting from direct coupling from the excitation coil, which can be experimentally determined. The remainder of the summing signal, which decreases as the lift-off distance increases, is induced by the secondary eddy current. This dependence on the lift-off distance is used to calibrate the differential signal, allowing for a more accurate characterization of the defects. Simulated experiments on a sample rail have been performed using a computer controlled X-Y moving table with the X-axis mimicking the train's motion and the Y-axis mimicking the train's vibrational bumping. Experimental results demonstrate the effectiveness of the new detection method.
常用于精密阻抗测量的交流电桥技术已被应用于开发一种用于铁轨缺陷检测的涡流传感器。与传统传感器仅使用一个检测线圈不同，我们使用两个检测线圈，这样就能平衡掉对应正常铁轨的大基线信号。通过使用数字锁相放大器算法检测和解调由铁轨缺陷引起的两个线圈的差分信号，我们显著提高了涡流检测方法的灵敏度。我们还探索了通过使用检测线圈的求和信号来测量提离距离，以补偿由于振动导致的涡流传感器提离效应。求和信号的主要成分是由激励线圈直接耦合产生的常数，可通过实验确定。求和信号的其余部分随着提离距离的增加而减小，是由二次涡流感应产生的。这种对提离距离的依赖关系用于校准差分信号，从而更准确地表征缺陷。使用计算机控制的X-Y移动台在样本铁轨上进行了模拟实验，X轴模拟火车的运动，Y轴模拟火车的振动颠簸。实验结果证明了这种新检测方法的有效性。
