Effect of wheat bulk density on the accuracy of moisture measurement via the microwave method
摘要
The article examines the effect of wheat bulk density (grain material density) on the accuracy of microwave moisture measurement. The method of microwave moisture measurement is based on amplitude dielectric metrology that analyzes the attenuation of an electromagnetic wave passing through grain material. A single-parameter moisture meter designed for use in grain processing was developed to operate at microwave frequencies. A block diagram of the moisture meter is provided, and its operating principles are described. The design of the instrument implements a mathematical model that takes into account the electrophysical properties of grain material and the features of its interaction with microwave radiation at a fixed frequency. A prototype of the instrument was manufactured and tested under actual production conditions. Grain material of various densities was analyzed: 87, 116, and 145 kg/m3. It was experimentally found that with decreasing grain density, the relative moisture measurement error increases, especially at moisture levels of above 14%: at 18% moisture content and grain densities of 145 and 87 kg/m3, the relative measurement error amounted to 9.8% and 44.7%, respectively. The calculated partial derivatives of the measurement signal amplitude with respect to density are significantly higher at high moisture levels, which indicates that moisture meter readings are highly dependent on material density under these conditions: at high moisture levels, even a small change in density can significantly increase the measurement error. Graphs are presented showing the dependence between the signal amplitude and moisture at different densities, as well as the results of regression analysis confirming the need to take density into account during instrument calibration. The absolute and relative moisture measurement errors were estimated depending on grain material density. The study confirmed the effectiveness of the microwave method for rapid moisture assessment and the developed moisture meter, provided that the effect of density is corrected.