| Grain moisture detection technology is a technology involves a variety of disciplines. Now, China’s grain moisture measurement or rely on manual testing, or dependence on imported equipment. The existing grain moisture meters most are laboratory applications moisture meter and portable moisture meter, but the practical application of higher-value-line measurement of moisture meter. It is really able to achieve online moisture measurement, and accuracy and stability to achieve the national requirements of the food line measurement of moisture meter and even fewer. In view of this situation, this paper designed a system of online testing of grain moisture.In this graduation project, the author makes a systematic study on the grain moisture online detection technology. Analysis of The theory of the dielectric properties of grain was analysised and capacitance method measurement of grain moisture was used. The direct-current charge and discharge small capacitance measurement method was chosen, after Comparing several common small capacitance measurement methods. On this basis, the author designed a grain moisture online testing system.At first, this article studied the differences of dielectric properties between grain and water. Then the variable dielectric capacitance sensor method was chosen to measure grain moisture. The hardware and software design on grain moisture detection system was systematic introduced. The hardware design included two parts, analog circuit design and digital circuit design. The analog circuits design related to the small capacitance detection circuit design, the clock signal circuit design, zero adjustment circuit design and real-time control interface design. The digital circuit design included sampling limiter circuit design, digital display circuit design, single-bus digital temperature sensor circuit design and RS485communication circuit design. The software design section contained a temperature acquisition module, water sampling module, the data processing module, the digital display module and PC communication module. Secondly, with the experimental design and a large number of experiments, the law of the capacitance sensor temperature drift was founded, and a software compensation method was designed for temperature compensation, by which the reliability of temperature drift law was verified. The author prepared grain samples of various moisture, the relationship between output voltage and moisture changes was obtained. Finally, the error analysis of experimental results was achieved, and future research directions of grain moisture online measurement were put forward.In this paper, the grain moisture detection system designed by the author can easily test different grain moisture content under the premise, and measurement repeatability is better. |
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