The infl uence of bulk density of wheat grain on the accuracy of moisture measuring by the microwave method
Аннотация
The effect of the density of wheat grain on the accuracy of measuring its moisture content by the ultra-high frequency method is considered. The method is based on amplitude dielectric metrology, in which the attenuation of an electromagnetic wave passing through the grain is analyzed. A single-parameter moisture meter operating at ultra-high frequencies and intended for use in grain processing production has been developed. The structural diagram of the moisture meter and the principles of its operation are presented The device's design incorporates a mathematical model that takes into account the electrophysical properties of grain material and its interaction with ultra-high frequency radiation at a fixed frequency. A prototype of the device has been manufactured and tested in real production conditions. Grain with different densities, such as 87, 116, and 145 kg/m3, has been investigated. It has been experimentally established that as the grain density decreases, the relative error in measuring its moisture content increases, especially at high moisture contents exceeding 14 %. At a moisture content of 18 % and a grain density of 145 and 87 kg/m3, the relative error in measurement was 9.8 % and 44.7 %, respectively. The calculated partial derivatives of the signal amplitude with respect to density are significantly higher in conditions of high humidity, which indicates a strong dependence of the moisture meter readings on the density of the material in these conditions: even a small change in density can significantly increase the measurement error at high humidity. Graphs of the moisture meter signal amplitude dependence on humidity at different values of density and the results of regression analysis confirming the need to take into account the density during the instrument calibration are presented. The absolute and relative errors of moisture measurement are estimated depending on the sample density. The results of the studies confirm the effectiveness of the ultra-high frequency method of rapid moisture assessment and the developed moisture meter, provided that the infl uence of density is corrected.