On The Online Determining Method Of Water Content Of Grain Based On Non-Uniform Electric Field

The grain-drying machine is one of important implements in the process accomplishing the mechanization of grain production. The mechanization of grain drying has become the bottleneck of the mechanization of whole grain production process in China. Although some tower drying machines have been used at present, but natural drying method has been applied to dry grain in our vast countryside. The thing accounting for the occurrence is that the machines do not tally with our actual situation. In order to accelerate the construction of a new socialist countryside and accomplish the mechanization of agriculture, experts proposed the idea of pin drying machine which tallies with our actual situation and carried out a lot of researches. But the traditional capacitor method of on-line determination of the water content of grain is not applied to that in pin drying machine because of its operating principle and structure. Therefore, the research of a new method of on-line determination of grain water content suitable for pin drying machine has become a task which brooks no delay confronting us.The charging patterns and their characteristics are studied deeply beginning with the research of the electric properties of grain under uniform electric field in this paper. It is put forward that the charging patterns of grain have polarization charging, friction charging and vital charging in light of that the characteristics of grain are between dielectric and organism. The polarization charging is caused by the directional movement of carrier and orientational polarization of dipole jointly. Their contributions are related with the vital characteristics of grain. When the water content of grain is lower, the vital characteristics of grain is weak, it is considered as dielectric. The orientational polarization of dipole is major contributions in the polarization charging. And when the water content of grain is higher, the vital characteristics of grain is strong, it is considered as organism. The concentration polarization increases at this moment. The directional movement of carrier is major contributions in the polarization charging. Friction charging is a charging pattern which exists widely. It exists in relative movement of grain. Although there is not an authoritative explanation of the formation cause of friction charging, but we can find its law by experiments. The charge character of friction charging of grain is related with the dielectric constants of grain and frictional material. When dielectric constant of grain is greater than that of frictional material, grain charges are negative. Whereas dielectric constant of grain is less than that of frictional material, grain charges are positive. The charge quantity of friction charging of grain is related with the quantitative difference between the dielectric constants of grain and frictional material. The larger the difference is, the more the charge quantity is. The vital charging is one of manifestations of biological behavior. It is caused by the potential difference of membrane, which maintains matter exchange between the inner and the outer of cell membrane. Therefore, vital charging has close relation to the water content of grain. Beginning from safe water content of grain, the charge quantity of vital charging increases with the increase of the water content of grain.On the use of the electric properties of grain, the cleaning-grading and water determining of grain are introduced mainly. There are many studies of the cleaning-grading of grain, but its use is not seen basically. There is not a parameter, which reflects separate level and is used to guide the design on the development of the cleaning-grading machine of grain. By using of experiment, the parameter that consists of polarization force and grain mass, the ratio of polarization force to mass is proposed in this paper. The ratio of polarization force to mass should be the quantitative parameter on the design of cleaning-grading machine of grain. The experimental results show that there are the remarkable differences of the polarization force and the ratio of polarization force to mass between good grain and bad one. Determining the ratio of polarization force to mass of some grains is carried out in the paper. The quiescent determining technology matures basically and there are commodity machines on sale on the determining of the water content of grain. Although the on-line determining has been used in some large drying machine, for example tower drying machine, but the error is as high as 1.5% because of the difference of research condition and the lag of corrected measure. It is important that all traditional determining devices of water content based on the electric properties of grain use the structure of parallel flat capacitor. This limits to its use on many drying machines, for example pin grain drying machine. We try to find a new on-line determining method of the water content of grain with the introduction of the uses of the electric properties of grain.In this paper, proceeding from the requirement of the structure of pin grain drying machine, the method of on-line determination of grain water content is proposed based on non-uniform electric field; the theoretical researches and a lot of experiments are carried out on the electric properties of grain under non-uniform electric field; and the sensor of the water content of grain which has the level electrodes at the same plane and its measure system are designed and tested at the same time. The theoretical core of the determining method of the water content of grain based on non-uniform electric field is the electric properties of grain under non-uniform electric field that is produced by double electric axes. Consulting the electric properties of grain under uniform electric field and according to the operating characteristics of pin grain drying machine, 4 influence factors are determined, they are determining frequency, grain water content, electrode gap and grain layer thickness. For convenient research, the special determining device is designed that consists of the sensor of the water content of grain that has the level electrodes at the same plane and its measure system. Author conducted the theoretical researches on the electric properties of grain under non-uniform electric field by the knowledge of dielectric physics and biophysics. The equipotential lines of the electric field caused by double electric axes are 2 eccentric circle family lines that are mutual inversion. The extremum points of the polarization charge density of grain surface appear in the points of tangency that are the circle that the center of circle is at the center of electric axis and grain surface. The influence of determining frequency on electric properties of grain under non-uniform electric field is obviously different from that under uniform electric field. The relationship is not logarithmic function, whereas is inverse function. Author explains the formation cause of the relationship from microstructure by using the theory of phonon and potential barrier and the doctrine of high polymer. And the fitting on the experimental results is carried out. The coherence of fitting results is of high significance. When the determining frequency is higher, the difference of the electric properties of rice is less. The influence of the water content of grain on electric properties of grain under non-uniform electric field is not logarithmic function, whereas is 3 order multinomial. This result is that of dynamic equilibrium that polarization, water content and non-uniform electric field affect together. The results of error analysis show that the error is less than 1%. The influence of the electrode gap on the electric properties of grain is related with the factor of the water content of grain. Theoretically the thinner the electrode gap is, the higher the precision is. But according to operating characteristic and the experimental results, the electrode gap should be moderate. The influence of the grain layer thickness on the electric properties of grain mainly is contact pressure and bulk weight. There is not the difference of the contact pressure in the level electrodes because the electrodes are at the same plane. The influence of the bulk weight only appears in high water content. Therefore, when the grain layer thickness is less than 50cm, its influence on the electric properties of grain is neglectful. According to operating characteristic of pin grain drying machine, the method of on-line determination of grain water content based on non-uniform electric field has the most significant relationship between the electric properties and the water content of grain and best effect at the determining frequency of 9000Hz and the electrode gap of 16mm.In this paper, the device of on-line determination of grain water content based on non-uniform electric field is designed, which consists of the sensor of the water content of grain which has the level electrodes at the same plane, the high frequency power supply, the standard resistance and the data processing system. By means of comparing and choosing, the best objective function is defined, that is potential difference of grain between the electrodes. The relationship between potential difference and water content of grain is 3 order multinomial. The fitting errors are less than 2.6% when the water content of grain is less than 23% and about 0.5% when the water content of grain is the safe water content. This is satisfied with the operating requirement of pin grain drying machine. Author still carries out the experiments of on-line determination of the water content of grain by the sensor of the water content of grain that has the level electrodes at the same plane and its measure system, and conducts the analysis of experimental errors. The grain breeds of 20912, Xudao 3 and Zhoumai 15 are applied in the experiments. By experiments, it is found that there is not a breed difference in the objective function of rice water content at the safe water content of grain, but the objective function of rice water content is different from that of wheat water content. This is good for the simplification of operating determining the water content of grain online in pin drying machine.