Design On Moisture Content Meter Of Coarse Cereals Based On Dielectric Properties

Coarse cereals, containing necessary nutrition elements for human bodies which are lackin major grains and beans, could be developed as healthy foods. Not only the quality ofcoarse cereals, but also the choises of technique of deep processing of them are affected bytheir moisture contents in the course of purchasing, transportation and storing. It is verymeaningful of moisture detecting of coarse cereals. There are some devices developed todetect the moisture contents of major grains, which are not suitable for coarse cereals. As aresult, it is very necessary to develop a moisture content meter which is high-precision andaimed at coarse cereals.It is feasible to detect the moisture contents indirectly by testing the dielectric constantof grains because the dielectric properties of grains have a close relationship with theirmoisture contents. The dielectric constants of grains are not only decided by their moisturecontents, but also related with some other factors such as variety, temperature and bulkdensity. Based on the above reasons, a moisture content meter of coarse cereals is designedbased on dielectric properties in this paper, considering the impact of bulk density andtemperature on detection accuracy. The main research contents and the results are as follows.(1) The hardware system of moisture content meter was designed. The system consistedof8-bit Single-chip Microcomputer AT89S52, capacitance detection module using directcurrent charging/discharging circuit, temperature detection module, mass detection module,analog-to-digital conversion module and input-output module. The system could show themoisture content of coarse cereals calculated on the base of detecting capacitance,temperature and bulk density.(2) The software system of moisture content meter was programmed using C51language,including main procedure, keyboard circulation scanning procedure, temperaturemeasurement procedurs, Liquid Crystal Display procedure, analog-to-digital conversionprocedure and moisture content calculation procedure.(3) The Printed Circuit Board of moisture content meter was designed by AltiumDesigner. Then the hardware system was made and the software system was debugged. Thetesting results showed that the moisture content meter running well. The detection accuracies of capacitance, temperature and mass detection were±2pF,±0.3℃and±0.2%F.S.(4) Millet was used to establish the mathematical model among capacitance, moisturecontent and temperature based on researching the influence on capacitance by moisturecontent, temperature and bulk density. The rationality of the model was tested. The resultsshowed that coefficient of determination of the model R~2was0.9852.(5) In the range of5~40℃, taking seven different millet samples in different moisturecontent (within11~20%wet.basis.) as test objects, the detection accuracy of coarse cerealsmoisture content meter was verified. Compared with the standard drying method, the resultsshowed that the detection absolute error of the self-designed moisture content detector wasless than0.5%and the respond time was less than3s.