A comparative study of polymer coated capacitive sensors for soil moisture sensing
Anindita Kalita, Moupali Chakraborty, Karabi Biswas · 2017
In this paper, a comparative performance analysis based on two different types of polymer, namely PMMA (poly methyl methacrylate) and DQN-60 coated capacitive sensor is reported to find out a low-cost sensor for soil moisture measurement. PMMA is readily available and inexpensive polymer which is coated on copper electrodes separated by epoxy to make the sensor. Statistical study shows that the root mean square error (RMSE) and percent normalized RMSE (%NRMSE) for polynomial fit of PMMA coated sensor is quite high. Size optimization of the PMMA coated sensor is studied here for better performance and improved RMSE. A simple signal conditioning circuit is proposed at this point to measure the capacitance change and produce the output in terms of voltage. The voltage to soil moisture calibration is done using thermo-gravimetric method.