高低频双频激励土壤含水率传感器设计与试验  

Design and Experiment of Soil Moisture Sensor Based on Dual Frequency Excitation

作　　者：盛庆元[1] 张西良[2] 杨越[1] 李萍萍[3] 倪梦瑶 SHENG Qingyuan;ZHANG Xiliang;YANG Yue;LI Pingping;NI Mengyao(School of Mechanical and Electrical Engineering and Transportation,Shaoxing Vocational and Technical College,Shaoxing 312000,China;School of Mechanical Engineering,Jiangsu University,Zhenjiang 212013,China;College of Forest Resources and Environment,Nanjing Forestry University,Nanjing 210037,China)

机构地区：[1]绍兴职业技术学院机电工程与交通学院,绍兴312000 [2]江苏大学机械工程学院,镇江212013 [3]南京林业大学森林资源与环境学院,南京210037

出　　处：《农业机械学报》2022年第4期228-234,共7页Transactions of the Chinese Society for Agricultural Machinery

基　　金：浙江省自然科学基金项目(LGN18E090001)。

摘　　要：针对现有电容式土壤含水率传感器对电导率敏感等问题,从电阻电容串联阶跃响应原理出发,采用峰值检测技术,设计高低频(100、50 MHz)激励下的数字型土壤含水率传感器,并提供一种融合高低频响应信号分析土壤等效相对介电常数的反函数模型。试验结果表明,传感器的高低频响应稳定时间在338~464 ms,建议传感器高低频切换间隔大于500 ms。在非导电液体介质中标定结果表明,高低工作频率下各自输出信号与液体相对介电常数符合指数模型,决定系数R^(2)大于0.98。在0~1000μS/cm范围内的溶液试剂中,基于反函数模型的高低频数据融合处理,电导率引起的测量相对介电常数的最大误差为1.775,对应最大引用误差2.16%。土壤实测表明,单频率传感器输出信号易受土壤电导率的影响,其引起的信号误差可大于100 mV,对应的体积含水率误差大于10%;而双频输出信号经反函数模型的数据融合处理后,结合Topp模型,电导率对传感器的影响最大误差为3.2%。In agricultural production,capacitive soil moisture sensor(CSMS)has received considerable attention,for it is relatively inexpensive and easy to operate,and can meet the application requirements of wireless sensor network.But CSMS is vulnerable to the soil temperature and salinity in the measurement process.Therefore,a CSMS was designed based on the principle of resistance capacitance series step response.It had two frequency square wave excitation signals,adopted peak detection technology,and took digital signal as output.An inverse function model was proposed to analyze the soil equivalent relative permittivity by fusing high and low frequency response signals.The experimental results in air and distilled water showed that the high and low frequency response stability time of the sensor was within 338~464 ms,and it was suggested that the high and low frequency switching interval of the sensor was greater than 500 ms.The calibration results in non-conductive liquid medium showed that the exponential model can well fit the relationship between the output signal and the relative permittivity of liquid at high and low operating frequencies,and the coefficient of determination R^(2) was greater than 0.98.In the range of 0~1000μS/cm,the maximum error of relative permittivity measurement caused by conductivity was 1.775 and the corresponding maximum quote error was 2.16%.The results of soil measurement showed that the output signals of high frequency and low frequency sensors were affected by soil conductivity respectively,and the change of output voltage signal can be greater than 100 mV,and the corresponding volumetric water content error was greater than 10%.After the proposed data fusion processing of the high-frequency and low-frequency output signals,combined with the Topp model,the influence error of conductivity on the sensor was controlled within 3.2%.

关 键 词：土壤含水率 峰值检测 双频激励 传感器 

分 类 号：TP212.2[自动化与计算机技术—检测技术与自动化装置]