作　　者： ; ; ; ; ;

机构地区： 教育部

出　　处： 《农业工程学报》 2013年第7期36-43,共8页

摘　　要： 土壤中的水分影响土壤养分的溶解、转移和微生物的活动,是作物赖以生存的基本要素。土壤含水率的快速准确监测对于农业生产具有重要意义。该文设计了一种基于RC网络相频特性的土壤含水率传感器。不同含水率的土壤的介电常数的变化会导致RC电路网络的相频特性的变化。传感器通过感知这种变化进而确定土壤含水率。此外,针对RC网络电路元件参数和工作频率选择的问题,该文采用最优化方法求解从而使传感器在量程范围内具有最佳的灵敏度。其中最优的工作频率为f*=1.9412×108Hz,最优的串联电阻R*=13.1Ω。试验表明,该传感器对砖红壤土含水率的预测模型的决定系数R2为0.9889,实际预测误差≤4.58%。 @@@@Dielectric-based methods are widely used due to their non-destruction, efficiency and accuracy. The capacitance of the probe on the sensor is affected by the soil moisture. Therefore the mathematical model can be built between the capacitance of the sensor and the soil moisture. In this paper, a new soil water content sensor based on the phase-frequency characteristic of RC network is proposed. The sensor consists of four parts, that is a VHF oscillator, a phase-detecting circuit, a first-order RC low-pass circuit, and a probe. The VHF oscillator outputs a frequency-specified f＊ signal to drive the RC network, and the capacitor C of the first-order RC low-pass network is replaced by the capacitance of the probe of the sensor. Moreover, the changes of capacitance of the probe brought by the change of the soil moisture will cause a significant change in the phase-frequency response of the RC network. The AD8302 phase-detector is used to measure the change of the phase-frequency response of the RC network by converting the phase angle of the RC network to a voltage signal. Thus, the relationship between the soil moisture content and the output voltage signal can be built to estimate water content in soil. Compared with existing published works on the theoretical implementation which has low accuracy and sensitivity of the sensor, the proposed sensor is optimized by the following steps：1） The measurement equivalent circuit model of the first-order RC low-pass circuit along with the input equivalent circuit of AD8302 is built;2） The relationship between the output voltage signal of AD8302 with the phase-frequency response of the measurement equivalent circuit with a specified frequency f and the resistor R of RC network is derived; 3） Formulating the optimization problem by maximizing the integration of change of the output voltage of AD8302 in the entire predefined variation range of the capacitor C of the RC circuit, 1 × 10^-12 F〈C〈 1× 10^-8 F, subjecting to fand R; 4） Solving the objective

关 键 词： 传感器 设计 土壤含水率 网络 相频特性

领　　域： [农业科学] [农业科学]