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在磁感应成像系统中,有用的二次磁场十分微弱,都淹没在主磁场中,因此采用微弱信号检测技术中的锁相放大器来提取。本研究以电子开关为相敏检波核心,利用相敏检波、锁相环、直流放大滤波、AD采样等电路模块,构成了精度高的模拟锁相放大器。该系统检测有效值10~1 000μV频率为1kHz的正弦信号,其误差在2.6%以内;输入相同幅值频率为1.05kHz的噪声信号,其误差最大在3%以内;输入10倍幅值1.05kHz的噪声信号,对测量结果有一定影响,其误差最大8.6%。所以,基于电子开关式锁相放大器有很好的噪声抑制能力,能够在强噪声背景下提取出特定频率微弱信号。
In the magnetic induction imaging system, the useful secondary magnetic field is very weak, are submerged in the main magnetic field, so the weak signal detection technology to extract the lock-in amplifier. In this study, the electronic switch is the core of the phase-sensitive detection, and the phase-sensitive detection, phase-locked loop, DC amplification filter, AD sampling and other circuit modules are used to form the analog lock-in amplifier with high precision. The system detects RMS 10 ~ 1000μV frequency of 1kHz sinusoidal signal, the error is less than 2.6%; input the same amplitude frequency of 1.05kHz noise signal, the maximum error of less than 3%; 10 times the input amplitude of 1.05kHz Of the noise signal, the measurement results have a certain impact, the maximum error of 8.6%. Therefore, the electronic switch-based lock-in amplifier has a good noise suppression capability, can be extracted in a strong noise-specific weak signal frequency.