Design of Orthogonal Lock-In Amplifier for Weak Eddy Current Signal Detection
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摘要: 涡流检测是一种广泛应用的常规无损检测技术, 涡流传感器输出微弱信号的检测是整个系统的关键。设计了一种基于互相关原理的模拟正交锁定放大器, 其采用数字频率合成器AD9854发生正交参考信号, 通过模拟乘法器AD734进行互相关运算, 利用低通滤波器MAX291获得的同相直流分量和正交直流分量。对两路直流分量进行运算, 可以得到涡流信号幅度和相位的变化量, 从而判定待测对象的特征。通过涡流检测试验应用, 结果表明, 该放大器可方便地应用于涡流检测系统中, 性能可靠, 工作频率可达5 MHz。Abstract: Eddy current test is a kind of general non-destructive test technique which is widely adopted in a range of industrial applications and the detection of the output weak signal of eddy current sensors is a key element in test system. An analogy orthogonal lock-in amplifier was designed based on cross correlation theory. It applied direct digital synthesizer AD9854 to generate orthogonal reference signals, analogy multiplier AD734 to conduct cross correlation operation and low pass filter MAX291 to get the in-phase direct current component and the orthogonal direct current component. By processing these two direct current components, variations of eddy current signal amplitude and phase could be gotten, then, the character of UUT could be judged according to these variations. The eddy current test experiments showed that this amplifier could be applied in eddy current test system conveniently and reliably, and the work frequency could approach to 5 MHz.
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