| Moisture content is one of the important parameters that affect the quality of grain storage,transportation,and processing.Bulk density and multiple reflections of electromagnetic waves are two main interference factors that affect the accuracy of microwave method for measuring grain moisture content.A method for measuring grain moisture content based on microwave spatial traveling standing waves is proposed,which eliminates related interference.A grain moisture content detection system has been developed to achieve rapid,non-destructive,and high-precision detection of grain moisture content.The device has a simple structure and does not require the use of a vector network analyzer.The measurement system is divided into three parts:a microwave detection unit,a signal analysis unit,and an interactive interface for grain moisture content.The system consists of a microwave cavity oscillator,a transmitting and receiving horn antenna,a slide rail,a stepper motor,a motor driver,and modules such as weight detection and temperature detection.The microwave detection unit uses X-band microwave and transmits the obtained microwave signal through a zeroing amplification circuit designed by the device;The signal analysis unit uses the GD32F303RCT6 chip as the core controller,and implements microwave data acquisition,system control,data processing,and data transmission functions for grains through hardware circuit and software programming.The interactive interface for grain moisture content is implemented through C#language and the.Net core framework to display relevant data to users,and through RS-232 protocol to achieve data communication and device control between the upper computer and the single chip microcomputer.In this paper,wheat and soybean were selected as research objects.Based on the phase shift and attenuation of traveling wave standing wave nodes caused by multiple reflections during microwave transmission,a moisture density independent equation for grain was established through multiple regression analysis.For wheat with a moisture content between9.3%and 25.3%,the goodness of fit R~2of the measurement equation is 0.975.Compared with the direct drying method,the measurement result has a performance standard error SEP of0.983%;For soybeans with a moisture content between 10.3%and 27.7%,the goodness of fit R~2is 0.995,and the performance standard error SEP is 0.564%.The detection method proposed in this paper can achieve fast,non-destructive,and high-precision detection of grain moisture content;The measurement system can complete the measurement in a few seconds,and the portable structure of the device enables it to be flexibly applied in fields such as agriculture and industry. |
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