基于时域传输原理的土壤水分测试仪研究  

Soil Moisture Meter Based on Time Domain Transmission Principle

作　　者：冯磊[1] 杨卫中[1] 石庆兰[1] 董乔雪[1] 徐云[1] 高红菊[1] 

机构地区：[1]中国农业大学大学信息与电气工程学院,北京100083

出　　处：《农业机械学报》2017年第3期181-187,共7页Transactions of the Chinese Society for Agricultural Machinery

基　　金：国家自然科学基金项目(31371531)

摘　　要：为利用时域测量技术实时、快速、准确地测量土壤水分,设计了一种低成本的基于时域传输(TDT)原理的土壤水分测试仪。仪器的探头采用末端封闭的回路结构,信号在探头上单程传输,通过测量电磁波在土壤介质中的传输时间测量出土壤的介电常数,再通过土壤标定方程得到土壤水分。时域传输仪由高频脉冲信号源、同轴传输线、U型回路结构探头、以TDC-GP2时间间隔测量芯片为核心的传输时间测量电路和以LPC2132 ARM微控制器为核心的控制电路组成。通过标准溶液测试和土壤测试试验,验证了双U型探头的测量结果好于单U型探头,仪器使用双U型探头测量传输时间的均方根误差为43.9 ps,测量介电常数的均方根误差为0.791,使用TOPP方程测量砂土土壤含水率的均方根误差为0.029 cm^3/cm^3,测量壤土土壤含水率的均方根误差为0.039 cm^3/cm^3。结果表明设计的时域传输土壤水分测试仪可以准确地测量土壤介电常数和土壤体积含水率。In order to measure the soil moisture in real time, quickly and accurately by using time domain measurement technique, a low cost soil moisture measuring meter was designed based on time domain transmission （TDT） principle. The probe of TDT meter adopted structure of closed loop, so that the signal was transmitted on the probe in one way. The permittivity of soil was measured by measuring the transmission time of electromagnetic wave in soil medium, and the soil moisture was obtained through soil calibration equation. TDT meter was composed of a high frequency pulse signal source, a coaxial transmission line, a probe in U-shaped loop structure, a transmission time measuring circuit using TDC - GP2 time interval measurement chip as the key component and a control circuit using LPC2132 ARM micro controller unit as key component. Through the standard solution test and soil test, it was proved that the measurement results of TDT meter with double U-shaped probe were better than those of single U-shaped probe. The root mean square error （RMSE） of transmission time measurements by using TDT meter with double U-shaped probe was 43.9 ps, and the RMSE of dielectric constant measurements was 0. 791. Using TOPP equation, the RMSE of soil moisture measurements in sand soil determined by TDT meter was 0. 029 cm^3/cm^3 , and the RMSE of soil moisture measurements in loam soil determined by TDT meter was 0. 039 cm^3/cm^3. The results showed that the soil permittivity and soil moisture could be measured accurately by using TDT soil moisture measuring meter.

关 键 词：土壤水分 时域传输 时间差测量 介电常数 

分 类 号：S237[农业科学—农业机械化工程]