Study On Purple Soil Moisture Content Measurement Based On Microwave Transmission Line Theory

The moisture content of soil is one important indicator of soil which plays an indispensable action in the production and irrigation of agriculture and research of basal theory. Take real-time monitoring in the moisture content of soil can promote the growing of corps, raise the operating factor of manure and avoid the wasting of water resource. The rapid and real-time measure of the moisture content of soil is the key in carrying out precision agriculture. China is an agricultural country so it is important in developing and exploiting a measuring technique about soil moisture which have good real time, low costs and high precision.This paper research the method of measuring moisture content of soil based on microwave transmission line theory and design the sensor and measuring system which according to the request of measuring soil moisture. Main work as follows:1. Through inquiring and reading a mass of documents we can obtain that the dielectric constant of soil is up to the soil water content and through the analysis of theory proves that using the microwave transmission line theory to measure the soil moisture is a rapid method of measurement which haves good real time and high precision.2. Through researching the theoretical to determine the relation of high frequency signal and the length of transmission line. The measuring soil sample chooses the purple soil which wide distribute in southwest. Designing different high frequency signal and corresponding transmission line length through theoretical analysis. Through experiments to fix the soil water content indoor and filter a least measurement error and higher precision frequency signal and corresponding transmission line length in sensor by contrastive analysis.3. Designs the hardware circuit of measuring system. The circuit of signal source to use MC1648 chip, the detecting circuit to use half-wave rectification smoothing circuit, the microcontroller choose dsPIC30F2010 chip, the video chipset choose HD44780. This hardware circuit haves advantages of simple structure and dependable performance and low cost.4. Using C language to progress software programming and modify it after debugging the hardware circuit.5. Using the measuring system in measuring moisture content of field farmland, comparing measuring result to oven drying method. Result shows that the measurement precision of this system satisfies basic require of design.