The Research On RF Technology Grain Moisture On-Line Detector

As a big agricultural country with a large population, food production and safety are directly related to the stable development of China’s national economy and the people’s livelihood and society. Food is the fundamental guarantee for the country all the time. The moisture of grain is an important standard of food safety. When the moisture of grain is too high, it will make the chemical reaction internal and make the grain cell metabolism strong, producing heat, which also leads to metamorphism and causes serious losses. On the contrary, when the moisture of grain is too low, it may lead to the destruction of the organic in the grain and reduce the grain quality.The traditional grain moisture detection method has the disadvantages of long testing period, low precision, low stability, being difficult to realize online detection and so on. Based on the above problems, a set of Grain Moisture On-line Detector based on RF technology was developed in this paper. The main contents are as follows:(1)The design of structure and function of the system: The system mainly included moisture meter in radio frequency type, master computer, sending and receiving module of GSM wireless short message. Moisture content of the grain was detected By RF type of moisture meter and then the information collected by serial port was transmitted to the host computer. Moisture content detected by RF type moisture meter was transmitted to the user mobile phone by sending and receiving module of GSM wireless short message.(2)The hardware design of the system: The hardware part included host computer and lower computer. Lower computer using modular designing method and STC89C52 RC single-chip microcomputer was chosen as the core model, designed the hardware circuit of the system lower computer. Radio-frequency signal source, Power divider, reflection bridge, phase comparator, signal amplification, V/F conversion circuit and other signal generation and processing units are combined. Power supply circuit, serial communication circuit, and so on were combined to form a complete moisture detection circuit, while the system can be connected with the GTM900-C wireless GSM module, and realize the wireless communication function of short message transceiver. The host computer mainly realized the function of receiving, processing, displaying data and so on.(3)The software design of the system.:According to the function of lower computer, the software design of system mainly consisted of host computer and lower computer. Lower computer also used the modular design method and C Keil programming software was used to writing program for Single-chip, whose main functions were collecting signal, sent signal to the host computer and receiving the command of the host computer. The command included the main program, initialization subprogram, signal acquisition procedure, SMS rounds of program and serial communication program, main program and subprogram combination. The whole ECU software forms. The functions of host computer were displaying and processing the data collected by the lower computer, LabVIEW was used for graphical programming, achieving communication with the next bit machine through the serial port. It mainly included the next bit machine frequency, data acquisition and data processing, storage and serial communication and so on. The host computer and the lower computer program were interacted with each other, forming a complete software system.(4) Calibration of moisture sensor: In the process of calibration, the determination method of grain moisture content was strictly followed by Inspection of grain and oilseeds& Methods for determination of moisture content. The value measured through Standard secondary drying method was chosen as the standard moisture value and the average value of the stored value of the upper computer was obtained after the abnormal data was removed, which were also compared with the standard value of the corresponding samples. Finally, the mathematical model of frequency and grain moisture content was established.(5) The performance test of the system: The purpose of performance experiment was to test the stability of the online detection and accuracy of the system. The moisture meter in radio frequency type was installed on the test device and grain dryer to test the static and dynamic moisture content of grain. The absolute error of the sensor and the performance of the online detection were obtained by the comparison between measured value and standard value. Besides, the function of receiving and sending short message was tested through the performance test. The test shows that the moisture content detected by this system compared with the oven method is less than 0.5% and the function of short message sending and receiving can be realized.(6) Conclusion: The stability and accuracy of the test system were tested by the performance test. Finally, the conclusion was drawn and the improvement of the system was determined.