一种工作频率可调的锁定放大电路在液体微弱电导测量中的应用

Frequency Programmable Lock-in Amplification Circuit for the Measurement of Liquid Low Electrical Conductivity

提出了一种基于直接数字合成（DDS）技术的锁定放大电路设计。该电路工作频率可在0～1．25MHz范围内调整，并具有自动相位跟踪的特点。该电路成功应用于液体微弱电导的高分辨率测量。实验结果表明，在1～50μS的测量范围内，电路的分辨率高于0．01μs。此电路作为一种通用锁定放大电路也适用其它类似的微弱信号检测应用。

Based on Direct Digital Synthesis （DDS） technique, a lock-in amplification circuit was designed with programmable working frequency between 0 and 1.25 MHz and automatic phase tracing ability. It was used for the measurement of liquid electrical conductivity. Experimental results show its resolution is better than 0. 001μS at the measurement range of 1-20μS. As a general lock-in amplifier design, this circuit can also be used for other applications where weak signals are to be measured.