Research on the soil moisture sensor of three-probe structure

Soil water sensors based on the theory of transmission line impedance are widely used in measuring soil water content. Therefore, it is critical to study structure and design methods of this kind of sampling probe in order to improve the measuring accuracy and sensitivity of the soil water sensor. Through studying on Parallel three-probe probe structure, the theory of impedance transform of transmission line and a mathematic analysis of a line quality from the parallel, a mathematical model for the impedance of the three-probe probe is developed. But it is impossible to accurately calculate the impedance value because the probe impedance is a multi-variable function. The optimal structure of three-parallel probe is designed by using the variance and range analysis of the orthogonal experiment of four factors and three levels. The experimental results show that the correlation of the optimal probe structure was close to linear, and provided a method for making sampling probe.