We present a methodology and a circuit to extract liquid resistance and capacitance simultaneously from the same output signal\nusing interdigitated sensing electrodes. The principle consists in the generation of a current square wave and its application to the\nsensor to create a triangular output voltage which contains both the conductivity and permittivity parameters in a single periodic\nsegment. This concept extends the Triangular Waveform Voltage (TWV) signal generation technique and is implemented by a\nsystem which consists in a closed-loop current-controlled oscillator and only requires DC power to operate. The system interface\nis portable and only a small number of electrical components are used to generate the expected signal. Conductivities of saline\nNaCl and KCl solutions, being first calibrated by commercial equipment, are characterized by a system prototype. The results show\nexcellent linearity and prove the repeatability of the measurements. Experiments on water-glycerol mixtures validate the proposed\nsensing approach to measure the permittivity and the conductivity simultaneously. We discussed and identified the sources of\nmeasurement errors as circuit parasitic capacitances, switching clock feedthrough, charge injection, bandwidth, and control-current\nquality.
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