A Self-Oscillating System to Characterize Liquid Salinities within a Single Triangular Waveform Signal

In this paper, we present a methodology and a circuit to extract liquid mixtures resistance and capacitance simultaneously from the same output signal using interdigitated sensing electrodes. The principle is based on the triangular waveform voltage signal generation technique where a current square wave is applied to the sensor and results in a triangular output voltage that contains both the conductivity and permittivity parameters in a single periodic segment. A closed-loop current controlled oscillator that operates on a single DC power supply implements this concept. The system interface is portable and only a small number of electrical components are used to generate the expected signal. As test examples, the electrical conductivities of saline NaCl and KCl solutions are characterized by a system prototype and benchmarked against a commercially available equipment. The results show excellent linearity and prove the repeatability of the measurements.