| Coarse cereals, including oats, buckwheat, red beans, black beans, lentils, beans and other minor miscellaneous crops do good to people health. Besides, coarse cereals contain not only the high nutritional value, but also some special nutrients which are important health food at present. As the special crops, it is essential that coarse cereals play the important role in the planting structure adjustment. Detecting of coarse cereals moisture is of great significance for the efficient utilization of coarse cereals resources. In spite that the drying method is of stable measurement and high accuracy, it is the traditional method for detecting of moisture of coarse cereals, which also has limitations in the need of quick measurement of moisture of coarse cereals. At the same time, the existing testing instruments of moisture mainly come from Japanese products and the price are very high. As a result, it is quite necessary to develop a kind of moisture meter that is high-precision. Based on the electric properties of agricultural production measurement of moisture, a moisture meter of the coarse cereals was developed successfully with low price, simple and convenient operation, quick and continuous measurement, considering the impact of temperature on detecting accuracy. In addition, the moisture prediction model was used to realize the detection of coarse cereals moisture. The main research contents and achievements are as follows:(1) The hardware system was designed in this paper. The whole system, whose core was8-bit Single-chip Microcomputer AT89S52and which was based on detecting capacitance, consisted of detecting capacitance circuit, detecting temperature circuit, A/D conversion circuit, MCU control circuit, keyboard input circuit, liquid crystal display circuit and lithium battery charging power supply circuit, achieving the hardware functions.(2) The software system which was developed by C51language, including main program, A/D conversion subprogram, temperature acquisition subprogram, liquid crystal display subprogram, and moisture calculating subprogram.(3) The PCB of moisture content meter was designed and manufactured by Altium Designer. After SMD components were soldered on the PCB, the hardware and software system were debugged together, and the detection range and accuracy of each detection module was tested at the same time. The results showed that the moisture content meter operated well, for example the range of capacitance detection was about20pF-160pF, and the accuracy of detecting temperature was±0.9℃; Rechargeable lithium battery is full after charging3h, which can be used continuously for about2.5h, finally, the charging module is fully able to meet the demand of portable instruments and daily working time performance.(4) The integrated shell of moisture content meter based on detecting capacitance was programmed by ProE for3D overall design, and it was combined with PCB board size in order that PCB board could match the instrument manufactured at last, and ultimately the two matched objects were installed successfully.(5) The oat was used as the sample to do the research about the influence of moisture content on capacitance. Those tests were conducted at different moisture content, from12.64%～20.73%, temperature range from5℃to40℃with5℃interval, and proved the effects of temperature and moisture content for the capacitor, meantime, established the relationship models between capacitor with temperature and water content. All the researches had examined the detection range and accuracy of moisture meter, by analysis a lot of testing data, which showed the coefficient of determination of the model R2was0.9897. At last, the testing results showed that, compared with the drying method, the absolute error of this designed moisture meter to measure the moisture content was±1.5%, and the response time was less than5seconds. |
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