Modelling and performance improvement of phase-angle-based conductivity sensor

In a previous work [1], a phase angle based conductivity sensing is reported, using a polymer (DQN-70) coated epoxy probe. That reported sensor is robust, light weight and low cost and its sensing technology is a simple and novel one. But, the sensing range is limited to low value (10 μS/cm to 1 mS/cm) and it needs high frequency excitation (200 kHz, 2 MHz and more). This paper aims to overcome those limitations. This work proposes an electrical equivalent model for the reported sensing system. Through this modeling, this paper analyses different aspects of said phase-based-sensing. The modelling also explains how the distributive capacitance of the system plays a key role in such sensing. It is shown that, the sensor performance (range and operating frequency) is improved by increasing the effective capacitance. The system is then modified accordingly and the concept is validated experimentally. The modified system senses higher range (10 μS/cm to 2.5 mS/cm) at only 200 kHz frequency.