The Design And Research On Grain Mositure Content On-line Measurig System Based On Pressure

Food is the major topic of people’s livelihood, food security storage is particularly important. Use of grain drying equipment to reduce grain moisture is an important part of safe storage of food. While in the process of grain drying, on-line monitoring of water is a main restricting issue. As the impact of complex factors, for conventional methods, fast online measuring and accurate control of moisture during drying are difficult.Therefore,using the application of modern new technology and theory method to detect the grain moisture content,solving the problems of the grain moisture detection and ensuring the drying process of food quality and economic benefits has very important significance.This research is based on the grain moistute measurement by the the pressure changes in the drying cabin,based on a large number of experiments discussing and proving the feasibiltiy and the theoretical relationship of measurement of grain moisure content by the lateral pressure coefficient.I developed the intelligent on-line measuring system of moisture content,the hardware includes the pressure sensor and MCU detection circuit and the software systmen inclueds the MCU program based on the C language and the PC software developed by the vitrual language of LABVIEW.At the same time,on the basement of a large number of experiments of the relations between lateral pressure coefficient and the grain moisutre,I establish a mositure prediction model based on BP neural network,it realize the temperature compensation and the nonlinear correction,improves the detection accuracy of the system. This paper studies the following:(1) Theoretical study of the lateral pressure coefficient measurement of grain moisture content.From the granary effect in the simulation of rectangular silos,make the experiments of the relations between the grain height and the different pressure changes in the bottom,the experimental results show tha:with the filling height increases, the trend of positive pressure and the lateral pressure is gradually becoming saturated,it is nearly the same as the trend in the circular silo. Through the experiment,it provied a feasible basis of grain mositure content by the lateral pressure coefficient. By carring out the experiment of the relations between the grain moisture content and the angle of repose,analysing the results of the experiment of the angle of repose under different mositure content conditions,the results show that:angle of repose for grain with grain moisture content increases monotonically increasing,while angle of repose is a grain internal friction characteristics of external performance.so,according to the coefficient of lateral pressure formula, grain internal friction angle is increased with mositure content. Therefore, the grain moisture content and lateral pressure coefficient is negative correlation, the lateral pressure coefficient with the grain moisture content increases.Finaly through the experiment based on the lateral pressure coefficient provided the academic basis to measure moisture content.(2) Design and research on on-line moisture detection system based on the lateral pressure coefficient,mainly to complete structure and circuit design of pressure moisture sensor.The hardware circuit includes the resistance strain gauge bridge circuit, the signal amplifying circuit, the analogue-digital conversion circuit, the linear photoelectric,the isolation circuit,the MCU data acquisition and serial communication circuit and so on;and the software system is composed by two parts,they are the master machine and slave machine,while the slave machine program is development by MCU C language, it complished the signal pretreatment and the communication function with PC,and the PC software is based on LabVIEW software platform,the it is the software who has the advantages of friendly man-machine interface and the simple and visual operation.This system realized the on-line grain moisture detection.(3) Establish the moisture prediction model based on the lateral pressure coefficient. By using the intelligent moisture measurement system,acquise the vertical pressure and lateral pressure frequence value under different conditions of grain height and moisture content,analyse the relations between lateral pressure coefficient and water content,the experimental results show that:the lateral pressure coefficient with the decreaseing of corn moisture content firstly decreases and then increases,it presents a trend like "V".During the range of corn moisture content from29%to23.7%, the trend of lateral pressure coefficient is declined,and during range the moisture content from23.7%to14.6%, the lateral pressure coefficient is monotonically increasing with rising curve.In the second phase,the trend of K which is lateral pressure coefficient is bascically the same as the trend of grain storage characteristic formula of lateral pressure coefficient with the changes of the moisture in theory. Under the conditions of grain height that is1.2meters and the moisture content that is14.6%～23.7%,making the experimental data regression analysis,the crrelation between the lateral pressure coefficient and c grain moisture content is very significant,the logarithmic relationship is one of the most significant whose R2reached0.957among them.Depending on a large number of data,establish a BP artificial neural network moisture prediction model based on the data merging technology,the model realized the non-linear correction and temperature compensation, made grain moisture measurement become more precise.(4) According to5HSZ small cross-flow grain dryer manufactured by Scientific Equipment Co., Ltd in Changchun, Jilin University,I made a field test of the system,the system is easy to operate, stable operation, and has a certain anti interference ability. It provides a new method and means for online moisture detection on the dryer.