根据活塞合金ZL108的变质质量与材料电导率呈单调函数关系的规律，利用电涡流原理检测ZL108的变质质量。研究应用移相、混频和滤波技术将电涡流传感器阻抗中的电阻分量和电感分量分离出来。设计的测量电路使传感器信号一方面与电源信号混频，另一方面与移相π/2的电源信号混频，并从前者获得电涡流传感器阻抗中的电阻分量，从后者中获得电感分量。最终确定根据电涡流传感器电阻的改变获得ZL108合金的变质信息，消除了电感分量的影响，提高了测量的准确性。

According to the monotone function relations laws between the metamorphic quality of piston alloy ZL108 and the material conductivity, eddy current testing was used to test the metamorphic quality. The research was proceeded by applying phase shifters, mixing, filtering technology to separate the resistance and inductance component from the signal tested by eddy current testing sensor. The circuit was designed to mix the sensor signal to power signal, so as to separate the impedance component; and also mix the sensor signal to π/2 phase shifter signal, so as to separate inductance component. Finally it was determined to use the resistance component to get the metamorphic quality information, thus eliminating the impact of inductance components and improved the measuring accuracy.