On-line Monitoring Device Of Grain Moisture Content In Combine Harvester In Using High Frequency Capacitance

The moisture content of grain is one of the important indexes for assessing whether grain can be harvested.Through the analysis of moisture content,the crop can be harvested at the best state and the quality of the grain can be improved.At the same time,grain moisture content is an important data that affects the accuracy of intelligent production system.Only when the weight of the harvested grain is converted to the weight of the grain with a fixed moisture content the yield information can be measured more accurate,and the cause of loss rate can be analyzed more comprehensively.Compared the domestic machine with other countries,the fact is that some latest combine harvesters designed in other states have installed the real-time grain moisture content monitoring system,while the majority of the domestic combine harvesters have not yet use this technology in practice.By virtue of the huge cost of introducing the measurement systems from other nations,the import of this machine cannot been applied in agriculture industry universally.Therefore,in the light of this situation,the research on the on-line monitoring of the grain moisture content of the combine harvester will be of great value in the domestic area to some extent.In this thesis,an on-line monitoring device of grain moisture content in combine harvester in using high frequency capacitance was designed.The device could monitor the moisture content in real time,and the monitoring results were displayed through the display module of the combined harvester's cab.At the same time,the CAN bus was used to transmit the data to the host computer for data processing.Moreover,the data was stored in SD card,which was convenient for subsequent data processing and analysis.The main research works of this thesis are as follows:(1)Based on the analysis of the working principle and harvesting process of combine harvester,the grain dynamic acquisition device was designed.The device realized the periodic sampling and discard of grain by utilizing the state of powerfailure of the electromagnetic circuit.And it was installed on the grain outlet of the combine harvester,so that grain could enter the sampling box continuously,thus ensuring the randomness of sampling samples.Study on the monitoring method of grain moisture content.In view of the special phenomenon of the operating environment of the combined harvester,the detection method and principle of grain moisture content were analyzed,and the detection principle of the charge and discharge of the capacitor plate with high frequency excitation signal was proposed.For the aim of simplify the circuit structure and reduce the cost,the high-frequency square wave signal was used instead of the traditional CMOS switching method.Especially,in order to improve the measurement precision of the monitoring device,the combination of software simulation and test verification was used to analyze the low frequency,intermediate frequency and high frequency excitation signals respectively.The high frequency signal with the frequency of 10 MHz was selected as the excitation signal of the monitoring device.(2)The hardware design of the grain moisture content monitoring system.It mainly included the selection of the microprocessor and the design of the peripheral circuit,the design of the high frequency capacitance grain moisture content sensor,the temperature sensor,the pressure sensor and the design of the anti-interference circuit.In order to analyze the influence of edge effect on the capacitive plate,the feasible approaches could be take advantage of a finite element analysis software COMSOL Multiphysics,established the capacitive plate and its working environment model.The orthogonal experiment optimization simulation of three-factor and three-level was carried out,by using capacitance ratio and sensitivity as the evaluation indicator.(3)The software design of the grain moisture content monitoring system.It mainly included the main program,the data acquisition and processing program,the storage and reading program of the SD card module data,the touch screen program and the CAN bus communication program.(4)The experimental study on grain moisture content monitoring system.The study could be divided into two parts: indoor static monitoring and on-field monitoring test.The indoor static monitoring test mainly included sensor calibration test,monitoring range analysis,static error analysis and system repeatability test.The indoor static monitoring test showed that the monitoring range of the moisture content sensor was 10%~30%,the maximum relative error was 1.57%,and the resolution was0.01%.The on-field monitoring test mainly included on-line monitoring accuracy test and system stability test.Among them,the maximum relative error of on-line monitoring for 2.07%,in accordance with the project design requirements(less than 5%).