I. INTRODUCTION

II. MEASUREMENT PRINCIPLE AND OPTIMIZATION METHOD

III. SENSOR DESIGN AND FABRICATION

IV. EXPERIMENTS

V. CONCLUSION

REFERENCES

Conductivity is a crucial parameter in water quality detection, which can roughly represent overall concentration of various inorganic ions. However, traditional conductivity sensors can only afford high performance measurement in a relatively low range while the concentration may vary much more in realworld water environment. This paper proposes a high-precision and wide-range measurement method based on a novel planar interdigital electrode sensor array and a self-adaptive algorithm. The array is composed of 3 pairs of planar electrodes with various cell constants aiming at different subdivided conductivity sections. The follow-up circuit and the self-adaptive algorithm keep the optimal electrode pair dominates the output of the array. Numerical simulations were utilized to optimize sensor parameters before fabrication. PCB manufacturing technique was used which guaranteed a relatively low manufacturing cost and stable performance. Experiments were conducted to verify the sensing performance and results showed that the array can maintain precise measurement from 0.5µs/cm to 500ms/cm.

INTRODUCTION

Conductivity is one of the most important parameters in water quality monitoring and aquatic environment protection. Since conductivity reveals amounts of inorganic ions in water [1], [2], it can acts as an indicator for water pollution. For example, if conductivity measured in a lake is much higher than the standard, it may suffer from water pollution like eutrophication. Similarly, sharp changing of conductivity implies a possible pollution event. Consequently, a quick and accurate conductivity measurement is of much help in water quality monitoring that makes some water pollution detectable at its early stage, while conductivity sensor is key device for it. Many forms of sensors for conductivity have been proposed in different research areas. M. Asgari and K. Lee proposed a fully-integrated CMOS electrical conductivity sensor for wet media that incorporated the sensing electrodes and the readout circuitry in the same die [3]. The detection range of the sensor spanned three orders of magnitude from 0.02 mS/cm to 10 mS/cm. Tejaswini et al. designed a capacitive-coupled probe for noncontact measurement of the conductivity of liquids [4]. Lin et al. used microfabricated platinum electrodes for a multifunctional sensor with ability of conductivity measurement [5]. Werner and Dean introduced genetic algorithm for a better performance [6]. Adhikary et al. utilized phase-angle to reduce noise [7].