GMR电涡流探头的零电势自动补偿技术研究

Research on Automatic Compensation of Remnant-voltage of GMR Eddy Current Probe

研究了以单片机为核心的GMR电涡流探头零电势自动补偿新方法。首先采用锁相放大技术获得零电势的幅值及其与基准信号的相位差;接着应用单片机控制数控移相器和数控幅值调节器改变基准信号的相位和幅值,获得与零电势一致的补偿信号;最后应用该补偿信号与零电势相减,使得此时的输出接近于零,实现了零电势的自动补偿功能。以铝板试件进行了检测实验验证。应用该技术进行零电势自动补偿之后,电涡流探头零电势的输出值约为补偿前的4.05%,补偿精度达到了检测实验系统的要求。表明该技术很好地实现了探头零电势的自动补偿,显著地提高电涡流检测系统的灵敏度,同时也增强了电涡流检测系统对深层缺陷的检测能力。

A new micro-controller based compensation method for remnant-voltage of the GMR eddy current probe was analyzed. Firstly, lock-in amplifier （LIA） technique was used to attain the amplitude of remnant-voltage and the phase difference between the remnant-voltage and the reference signal; Then, the micro-controller was applied to control NC phase-shifter and amplitude regulator to change the amplitude and phase of the reference signal, in order to obtain a compensation signal which was consistent with remnant-voltage; Finally, the output was close to zero after the subtraction between the compensation signal and remnant-voltage, and automatic compensation of remnant-voltage was achieved. Specimen aluminium was used in the detective experimental verification. After the automatic compen- sation of remnant-voltage by the technique, the output of the remnant-voltage of eddy current probe is about 4.05% of the one before compensation, the compensation accuracy fulfils the requirements of the detection system, which shows that the remnant-voltage compensation of eddy current probe can be realized by the technique and the technique improve the sensitivity of the eddy current system. Furthermore, it also can enhance the detection ability for deep-seated flaws of eddy current system.