基于RC峰值检测的土壤水分传感器设计与性能试验

针对现有电容式土壤水分传感器精度低、功耗高、价格高、标定过程复杂等问题,基于RC稳态响应峰值检测原理,设计了一款土壤水分传感器,并对传感器敏感区域、电学特性、标定模型、温度和电导率特性进行了测试。实验结果表明,传感器测量体积含水率平均灵敏度为12.187 mV,敏感区域为3.8 cm×2.5 cm×7.2 cm;输出信号不受供电电压影响,消耗电流仅为3~4 mA;通过在不同介电常数溶液中标定,结合TOPP经验公式,建立的指数标定模型的决定系数R^2均大于0.96;传感器温漂引起的测量误差约为0.5%,在0~2000μS/cm范围内电导率引起的最大测量误差小于4.2%,传感器最大实测误差为2.17%。

Design and Experiment of Soil Moisture Sensor Based on RC Peak Detection

For the modern intelligent irrigation system,a moisture sensor with high measurement accuracy,low power consumption,low price,small structure and simple calibration process is urgently needed.A capacitive low-cost soil moisture sensor and its signal processing circuit was presented based on the principle of RC steady-state response peak detection.The characteristic of the sensor circuit was that a RC series circuit realized slow charge and fast discharge by adding a discharge diode.The influence of the sensor's sensitive area,electrical characteristics,calibration model,temperature drift and conductivity on the output signal was tested.Experimental data analysis showed that the average sensitivity of the sensor for measuring volumetric water content was 12.187 mV,and the sensitive area was 3.8 cm×2.5 cm×7.2 cm;the output signal of the sensor was not affected by the supply voltage,and the current consumption was only 3~4 mA;by calibrating in different dielectric constant solutions and combining TOPP's empirical formula,based on working principle the exponential calibration model of the sensor can be well fitted to the relationship between relative dielectric constant and soil volumetric moisture content,and the determination coefficient R^2 was greater than 0.96.In the range of 5~50℃,the measurement error caused by the temperature drift of the sensor was about 0.5%.In the range of 0~2000μS/cm,the maximum measurement error of the sensor caused by conductivity was less than 4.2%.The measured data in Loess and cinnamon soil showed that the maximum error of the sensor was 2.17%.Compared with similar sensors,the test accuracy was comparable,and the cost-effective advantage was obvious.It was especially suitable for large-scale wireless soil moisture sensor detection systems.