Study On Soil Moisture Measuring Technique Based On Standing-Wave Ratio Theory

This thesis is supported by the foundation of National Advanced Technology Development Project(863 project, No. 2002AA2Z4071) and the conversion project of science and technology production of Science & Technology Ministry(No. 02EFN216901258). At first, through theoretical analysis on the soil dielectric property, it's proved that the real part of the dielectric constant in high frequency or microwave region can be used to measure soil moisture. It's a fast measurement method with high accuracy, wide applicability and little influence by the spatial variation of soil property. Then this thesis analyses the principle of the soil moisture sensor based on the standing wave ratio theory by standing wave and transmission line theory in microwave thechnology. At same time, the impedance model of probe with equaling length is built up that provides the theory basis for development of SWR soil moisture sensor circuit. For the sake of studying the characteristics of SWR soil moisture sensor, the soil cylindrical tube experiment is designed and the experiment modeling and performance analysis are done in this thesis.For the application of soil moisture measurement, the TSC-1 portable soil moisture measuring meter based on P89LPC925 MCU is developed. This meter not only can measure volumetric soil moisture fast but also can store data, communicate with PC and intelligently fast charge. Additionally to meet the demand of intelligence, digital and network communication in soil moisture monitor or irrigation control system, the intelligent soil moisture sensor based on RS-485 bus and information fusion technology is designed. The accuracy and reliability of the sensor are improved and the cost of installation is reduced.