| Shanxi is known as the kingdom of minor grain crops at home and abroad.And vigorously developing its superior grains is of great significance to the development of Shanxi’s characteristic agriculture.Moisture content is an important indicator of routine inspection in all links of grain purchase and storage.If the moisture content of minor grain crops is too low,its organic matter will be destroyed and its weight will be reduced.If the moisture content of minor grain crops is too high,the respiration of minor grain crops will be strengthened,causing problems such as heating,mildewing and insects.At present,there are many mature commercial moisture detectors on the market,but they are mainly used for main large cereal crops such as wheat and rice,and special moisture detectors for minor grain crops such as oats and quinoa are still relatively rare.Therefore,it is necessary to develop a minor grain crops moisture detector with good accuracy and reliable performance,which can achieve rapid on-site detection.In this paper,oats and quinoa are taken as the research objects.Based on the capacitance method,the design of the moisture detector for minor grain crops is designed.The principal research contents are as follows:1.The change of capacitance of minor grain crops with different moisture content(oats(8.83~ 29.14%))and quinoa(10.14 ~ 29.55%)at different frequencies(1~100k HZ)were measured by LCR meter,which was tested under the temperature conditions of 5~40℃.Under every excitation frequency,the multivariate regression mathematical model of capacitance,temperature and moisture content of minor grain crops was established by SPSS.The optimal excitation frequencies of oat and quinoa were 81 k Hz and 21 k Hz respectively.2.According to the capacitance measurement principle and the mathematical model of moisture content detection,the software and hardware of capacitive minor grain crops moisture detector is designed.MSP430F149 microcontroller is the core of the detection system.The AD5933 impedance measurement chip and the self-made concentric circle capacitance sensor constitute the capacitance detection module,the TFT touch screen is the display and control module,the DS18B20 temperature sensor is the temperature detection module,and the IAR software is the development platform.3.The accuracy of capacitive minor grain crops moisture detector tested by 105℃ constant weight method.10 samples of oats with different water content and 10 samples of quinoa with different water content were prepared respectively.Three temperatures were randomly selected within the temperature range of 5℃~40℃ to detect the moisture content of minor grain crops using the capacitive moisture detector designed in this paper.The results showed the average relative errors of the moisture content test results of oats and quinoa were 2.95% and 4.17% respectively.And the measurement time is less than 2s.The performance of capacitive minor grain crops moisture detector is satisfactory. |
