CAJ | 학술논문

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*=1.9412×108 Hz,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%.
토양중적수분영향토양양분적용해、전이화미생물적활동,시작물뢰이생존적기본요소.토양함수솔적쾌속준학감측대우농업생산구유중요의의.해문설계료일충기우 RC 망락상빈특성적토양함수솔전감기.불동함수솔적토양적개전상수적변화회도치 RC 전로망락적상빈특성적변화.전감기통과감지저충변화진이학정토양함수솔.차외,침대 RC 망락전로원건삼수화공작빈솔선택적문제,해문채용최우화방법구해종이사전감기재량정범위내구유최가적령민도.기중최우적공작빈솔위f*=1.9412×108 Hz,최우적천련전조R*=13.1Ω.시험표명,해전감기대전홍양토함수솔적예측모형적결정계수R2위0.9889,실제예측오차≤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 f and R;4) Solving the objective function by Genetic Algorithm (GA) to obtain the optimal f*=1.9412×108 Hz and R*=13.1Ω, making the sensor achieve the highest sensitivity and accuracy of the measurement of the changes of C due to the variations of the water content in soil. Experiments on the sensor are divided in the following two steps. First, the sensor is calibrated in a series of tested solution with different equivalent soil gravimetric water content, and the gravimetric water content prediction model is built as y=-79133x3-18141x2-1418x+0.5926 with the coefficients of determination R2=0.9889. Second, the sensor is evaluated in the soil samples with different gravimetric water content. The maximum prediction and average errors are 4.58%and 1.63%, respectively.