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

Abstract

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 °C to 80 °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 R2 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.

Free space traveling–standing wave attenuation method for microwave sensing of grain moisture content

“…The electric field in the space between the sample container interface and the radar receiving antenna has obvious characteristics of traveling-standing wave. The detection signal shows periodic changes as the antenna distance increased to approximately 14.3 mm (approximately equal to half the wavelength of microwave), and this finding is consistent with the conclusion of equation (7). In the process of grain measurement, the antenna needs to move more than 14.3 mm on the slide rail each time, and the maximum voltage value of traveling-standing wave in the first cycle can be obtained.…”

“…For the capacitance moisture meter, the sample is placed between two capacitor plates, which can be used for on-line detection. 7 However, the measurement results are affected by the structure and density of materials, and the accuracy will be reduced when the moisture content is low. The spectral moisture meter is designed according to the principle that water absorbs the infrared radiation strongly in the corresponding band.…”

Grain Moisture Measurement System With Robust Transfer Function, Invariant to the Change of a Physico-Chemical Grain Composition

“…Currently, a significant part of the means of measurement, which control substances' properties and composition, is occupied with measuring instruments that use capacitive sensors (Zambrano et al, 2019;Flor et al, 2022). It is pretty evident that the widespread introduction of versatile and accurate grain moisture meters and their proper operation will have a tangible technical and economic effect (Casada and Armstrong, 2009;Song et al, 2020;Li et al, 2021;Klomklao et al, 2017). 'Successful' modifications of capacitive sensors appeared years ago (Hegg and Mamishev, 2004).…”