针对金属管道的内、外壁缺陷的区分难题，采用脉冲涡流检测技术来区分内、外壁缺陷，设计了一套涡流检测系统。系统采用占空比为50%的矩形波作为涡流激励信号；设计了分别由涡流线圈和串联电阻组成的测量桥臂和参考桥臂；通过中央处理器（CPLD）进行除法运算得到差分电导，根据差分电导的不同波形，可以判断缺陷是位于管道内壁还是外壁。设计了信号采样时序，利用内检测器动态测试机构来评价涡流检测系统对内、外壁缺陷的识别程度。测试结果表明该脉冲涡流检测系统能准确区分出金属管道的内、外壁缺陷。

To solve the problem of distinguishing corrosion defects inside and outside the metal pipeline, a brand-new pulsed eddy current (PEC) system based on differential conductivity is established. The 50% duty cycle square wave is used as driving signal. A measuring bridge arm and a reference bridge arm composed of eddy current coil and series resistance are designed respectively. Complex programmable logic device (CPLD) is used to get differential conductance by using differential current divided by differential voltage. At last the eddy current signal sampling sequence is developed. A dynamic testing fixture with artificial defects carved on the pipeline is used to validate PEC system's accuracy. The differential conductance signal is displayed on the oscilloscope. Results show that the inside defect had two peaks, positive peak and negative peak, but the outside defect only had one positive peak. We can conclude that the brand-new PEC system has high accuracy in distinguishing inside and outside defects.