| "Hunger breeds discontentment,food safety first".Food security is also a great event related to national economy and people's livelihood.Rice planting area of China is about 330 million hectares.China is the world's largest rice growing country and rice is the main food.Rice moisture content is big after harvesting,if not timely and fully dry,easy to mildew.In recent years,due to the rapid popularization of agricultural mechanization and the spontaneous transfer of rural labor to the city in wide range,traditional artificial drying methods have been unable to meet the concentrate drying requirements of a large number of high moisture paddy,resulting in huge loss of rice.In order to improve the rice planting benefit,ensure national health and national food security,there is a urgent need to promote the mechanization of rice drying mode.In order to ensure the economic efficiency of rice drying process and the accurate and reliable of rice drying results,it is necessary to develop an economical and reliable rice moisture sensor.In this paper,a grain moisture sensor is designed to solve the problems of grain moisture measurement,such as cost,online,continuous.The concrete research content is as follows:(1)The determination of detection method for grain moisture.Through comparison of the basic principle,advantages and disadvantages of different grain moisture,analyzing the research status of grain moisture sensor designed by experts and scholars at home and abroad,and based on the design requirements of online measurement of grain moisture,choose capacitive grain moisture measurement method which has the advantages of simple structure,low cost,high reliability,convenient on-site maintenance,and suitable for on line continuous measurement of grain moisture.(2)Determination and optimization of grain moisture sensor structure.Through the comparative analysis of the advantages and disadvantages of different capacitive sensor structure,according to the test requirements of rice moisture,choose the coaxial cylindrical capacitive sensor.Through structure analysis of capacitive sensor,the optimization design scheme of coaxial cylindrical capacitance sensor is given.(3)Analyzing the influential factors of grain moisture detection and determining the best excitation frequency of grain moisture detection.Based on the influencing factors of grain moisture detection-the rice grain variety,density and temperature,a riceelectrical impedance spectroscopy experiment is designed.The change of the detection capacitance value with the excitation frequency(1Hz~1MHz),rice moisture(14%~28%)and temperature(40~80 ?)is obtained.The optimum excitation frequency of rice moisture is 2kHz,which provides a theoretical basis and data support for the determination of grain moisture detection model.(4)Determination of grain moisture detection model.Based on the multiple regression analysis method,using the experimental results of rice electrical impedance spectroscopy experiment,the the multivariate regression model is established by using SPSS,and the fitting degree is tested.The fitting procedure was good(933.02R(28))and the rice moisture detection model was established.(5)Hardware and Software design of grain moisture sensor detection circuit.Based on the principle of capacitive grain moisture measurement and the requirement of rice moisture detection,the hardware design composed of capacitance detection module,temperature detection module,control and display module and the software design composed of capacitance data acquisition,temperature data acquisition,data processing and display of capacitive grain moisture sensor detection circuit is completed by modular design.(6)Grain moisture sensor performance test.The moisture content of the rice is measured by the self-designed grain moisture sensor,and the results was tested by 105?constant temperature drying method.The results showed that the standard deviation of the absolute value of the detection error of the rice moisture sensor and the detection circuit is 1.514%,there is still a large detection error,need to be further optimized design. |
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