An Integrated Sensor Array for Water Quality Monitoring

Four important quantities in water quality monitoring are temperature, specific electrical conductivity (EC), total dissolved solids (TDS), and pH. In this paper, three sensors for precisely detecting these parameters were designed and fabricated in one structure. Spiral electrodes were made as temperature sensors and circular toothed electrodes were made as EC sensors. The pH sensor comprises two electrodes: the reference electrode (Ag/AgCl) and the working electrode (carbon black/highly porous polyaniline). The response time of the temperature sensor is 13.2 s, and the stability of the sensor is −0.031$\Omega {}^{\circ }{C}^{-1}$, and the sensitivity of the sensor is 0.003 $\Delta R{R}^{-1}{}^{\circ }{C}^{-1}$. The response time of the pH sensor was reported as 136.2 $s$ and the sensor's sensitivity was 8.8 $\mathrm{mV}p{H}^{-1}$ in the pH range of 4 to 10. Also, the best excitation frequency of 30 kHz and the best reference resistance of 1 $k\Omega$ were measured in the range of 100 to 2000$\mu Sc{m}^{-1}$ and the sensitivity of the EC sensor is ${10}^{-3}$ $\mathrm{cm}\mu S^{-1}$. TDS was also calculated from the specific electrical conductivity using the conversion factor of 0.66 $\mathrm{mg}\mathrm{cm}{L}^{-1}\mu S^{-1}$. Considering the electrical output of all sensors, a circuit was designed and built to receive their information. Operational amplifiers with different functions were used to create the reading circuit.