The Portable Measurement Instrument Of Grain's Moisture Content

Grain, as one of material base for the existing of mankind, is very important for all of us. The moisture content of the grain shall be taken as main basis for choices of safe storing and processing technology. Therefore, Test for moisture content is quite significant. Currently, direct and indirect test methods have been used very common. While, given the limited conditions (such as bulk size, long-time examination and expensive price), the two ways are not able to be applied universally in process of storing, purchasing and transporting for grain. It's especially true for individual transaction, when subjective judgement is adopt usually. But the inexactness of this subjective way cannot assure proper moisture in grain and causes enormous losses because too much moisture in grain will lead to heat. Accordingly, based on the results of previous studies, this paper takes mung bean as experimental subjects, searches the influence of the moisture content, temperature and bulk density on dielectric properties. AT89S52 is used as microcontroller core, the coaxial cylindrical capacitor is used as device to detect capacitance, DS18B20 to detect temperature and strain gauge sensors to detect weight, Keil C51 is used as the development of software to design a portable grain moisture content. At last, test the instrument precision.Based on the results of previous studies, this paper takes mung bean as experimental subjects. The instrument uses the device of coaxial cylindrical capacitor detection to design a new portable machine to test moisture of mung bean. Through the status of domestic and foreign research with the detection of grain moisture, analysis of various detection methods and technical characteristics of these detection ways, this paper take capacitance detection as the theoretical for this instrument. Because of it's low price and high sensitivity.Mung bean is used as experimental subjects, analyse the mathematical relationship of it's capacitance, moisture content, temperature and bulk density. In this paper, we put the mung bean by way of a free fall into the sensor and establish the mathematical model with its capacitance, temperature and moisture content under the no influence of test frequency.Design the hardware detection system as the core processor of AT89S52 microcontroller to measure capacitance, temperature and bulk density of mung bean and calculate it's moisture. The coaxial cylindrical capacitor was used to measure capacitance, digital temperature sensor DS18B20 was used to detect temperature, and the bridge circuit made by strain gauges was applied to detect mass, then the bulk density was calculated. However, this system contains A / D conversion circuit, liquid crystal display circuit and keyboard control circuit.Use C language to write the whole system software, which can combine the hardware circuit to achieve the full functionality of mung beans moisture content detection.Draw PCB by software of Protel, buy components and manufacture the instrument. Mung bean with moisture content from 10.0% to 20.0% is used as experimental subjects and is put by way of a free fall into the sensor. And test the instrument's precision at the temperature from 5 to 40℃. The instrument has a certain accuracy and it's absolute error is±1%.