Capacitively coupled contactless conductivity detection based on phase-sensitive demodulation principle

Based on the phase-sensitive demodulation (PSD) principle, a novel capacitively coupled contactless conductivity detection (C⁴D) system is developed to improve the measurement resolution and the detection range. The coupling capacitances formed by the metal electrodes, insulating pipe and electrolyte solution and the resistance formed by the electrolyte solution between the two metal electrodes can be measured. The influence of coupling capacitances on conductivity measurement is greatly reduced and the information of the coupling capacitance can also be obtained separately with the new system. Test results show that compared with the conventional C⁴D methods, the proposed method has the advantages of high resolution and wide measurement range.