A liquid conductivity measurement system based on electromagnetic induction

Electromagnetic measurement method was a non-contact biological tissue conductivity measurement technology. This paper presented a liquid conductivity measurement system based on electromagnetic induction; phase difference information of induced magnetic field was used as detection signal in the system. Firstly, the system was composed of excitation source based on directly digital synthesis, phase detector based on SR844 RF lock-in amplifier, excitation-detection coils sensor and signal processing circuit. Secondly, the maximum error of exciting source frequency accuracy was 2.4%, the phase drift of system was 0.001° /min, the phase resolution was 0.02°, the minimum conductivity could be detected by this system was 0.004S/m. Finally, the saline solution experiments of different concentration and different kinds of drinking water were made by this system, the experimental results demonstrated that the system could obviously identify category of water, and measurement results were consistent with the theory of electromagnetic field.