Design of Capacitive Paddy Moisture Sensor Based on Electrical Impedance Spectroscopy Analysis

The intelligent control of the paddy drying process is an prominent development trend and the accurate detection of paddy moisture content is the basis for the intelligent control of the paddy drying process. For the design of a paddy moisture sensor, electrical impedance spectroscopy experiments of the paddy variety Wu Yu Jing 3 (Oryza sativa L.) were conducted to optimize the excitation frequency and establish a paddy moisture detection model. By analyzing the change of paddy capacitance in moisture ranging from 14% to 29% over the frequency ranging from 100 Hz to 1 MHz with temperature ranging from 40 degrees C to 80 degrees C, 2 kHz is selected as the excitation frequency for paddy moisture detection in this study. Two-thirds of the experimental data points (i.e., 55 experiments points) at 2 kHz were modeled by regression analysis and the remaining one-third of the experimental data points (i.e., 28 experiments points) were used to evaluate the paddy moisture detection models. The R-2 of the paddy moisture detection model was 0.933 and the standard deviation of fitting test was 1.14%. A paddy moisture sensor was designed, and the standard deviation of the detection residual was 1.23%, which was close to the standard deviation 1.14% in the fitting test.