基于LVDS传输线延时检测技术的土壤含水率传感器  

Design of Soil Moisture Sensor Based on Detection of Propagation Delay in LVDS Differential Transmission Lines

作　　者：蔡坤[1,2] 徐兴[1,2] 俞龙[1,2] 岳学军[1,2] 

机构地区：[1]华南农业大学电子工程学院,广州510642 [2]华南农业大学广东省农情信息监测工程技术研究中心,广州510642

出　　处：《农业机械学报》2016年第12期315-322,共8页Transactions of the Chinese Society for Agricultural Machinery

基　　金：广东省科技计划项目(2014A020208110;2016A020210091)

摘　　要：为实现土壤含水率的快速准确监测,设计了一种基于LVDS差分传输线延时检测技术的土壤含水率传感器。该传感器将高频振荡信号分路为两通道LVDS差分信号,一个通道用于测试土壤含水率,另一个通道用于提供参考信号。由于土壤中水分的变化改变土壤介电常数,从而导致测试通道LVDS差分总线上信号传输延时的变化,则传感器检测该通道信号的传输延时就可以确定土壤含水率。为了获得LVDS总线设计线宽和线间距的最优值,以LVDS总线阻抗值均方误差最小化为目标,构建了线宽和线间距的最优化计算模型,并通过遗传算法求解出了最优线宽为0.178 9 mm和最优线间距为0.223 8 mm。试验表明,根据该参数设计的传感器在50 MHz频率时,对体积含水率8.31%以上的砖红壤土和黄壤土的预测模型为线性模型,决定系数R2为0.964 2,绝对预测误差在2.45%以内。Water in soil is vital for plants. Plants utilize the water absorbed from the soil for transpiration and producing necessary carbohydrates for plant growth. Soil moisture measurement is important to agriculture and gardening. Numerous soil moisture testing methods were researched and developed. These methods can approximately be categorized as dielectric-based methods and non-dielectric methods. The dielectric-based methods are widely used due to their non-destruction, efficiency and accuracy. The proposed method belongs to the dielectric-based methods. Since the dielectric permittivity of water is far larger than that of dehydrated soil, the permittivity of the mixture of water and soil is mainly determined by the quantities of water in soil. Moreover, the permittivity of dielectric material affects propagation speed of electromagnetic waves. The velocity of electromagnetic wave will be decreased when it travels in dielectric material with large permittivity value. The decrease of velocity of electromagnetic waves is highly related to the soil moisture. The proposed sensor provides a method for measuring the deceases of electromagnetic speed. The sensor consists of eight parts, which are a HF oscillator, two high-speed comparators, two LVDS transmitters, a LVDS differential transmission line for test, a LVDS differential transmission line for reference, two LVDS receivers, a phase detection circuit, and a mean-responding power detector. HF oscillator gives a signal to the inputs of two high-speed comparators simultaneously.

关 键 词：土壤含水率 LVDS差分传输线 传输延时 传感器 

分 类 号：S274.2[农业科学—农业水土工程]