Research On Capacitive Corn Moisture Measurement System

Corn moisture content is the main factor of effecting corn safe transportation and storage, and is also an indispensable measurement part when it is used to feed, food and industry. Corn is one of the main grain crops. Due to large particle size, it will produce large gap during measuring moisture content. Because air has much influence on dielectric constant of the device, moisture content is not precision. In all kinds of corn moisture measurement methods, capacitance method becomes the main method with simple structure, low cost and online measurement. This paper designs capacitive corn moisture measurement system, including hardware and software design. According to measurement data, I analyze factors of affecting corn moisture, such as, the capacitance value, temperature and volume weight. Using multiple regressions establishes relationship between corn moisture and influence factors. The research content and the results are as follows:1. Study on basic methods of corn moisture measurement and measurement circuits, design and optimize structure of capacitive moisture sensor.2. According to the requirements of the system corn moisture measurement, design hardware circuit, including peripheral circuit of MSP430F135, capacitance detection circuit, temperature detection circuit and power circuit. Analyze the detail of working principle and draw the relationship of the capacitance detection circuit output voltage and the input capacitance, the relationship of temperature detection circuit output voltage and input temperature.3. Measurement system software is mainly to receive output signals of the capacitance detection circuit and temperature detection circuit, save the results after modulus converting, through the communication interface to the computer for processing the experiment data.4. According to the requirements I deploy twelve corn samples of different moisture content. Acquire experiment data five times in five temperatures, weigh the corn sample and record results. I can use Dixon standards to process the experiment data. The relationship curves and equations of corn moisture content and sensor capacitance at the same temperature, moisture content and volume weight at the different temperatures are obtained by the least square fitting method. Analyze factors of influencing corn moisture measurement system and establish regression equation between the corn moisture content and capacitance value, temperature, and the volume weight.5. Compare with moisture measurement value of dry method and verify the accuracy of the corn moisture measurement system. It will conclude that moisture content ranges from10%to35%, measurement error is less than±0.03. While high moisture content increases measurement error in the system.