摘要本文在驻波原理的基础上设计出了一种成本低、精度高、稳定性好、适应性强的土壤水分速测仪。通过对介电物理学的理论分析，提出了土壤水分介电测量的等效电路和电磁波的最佳测试频率。在此基础上，建立了土壤水分传感器的测量装置模型，并通过计算传输线的特征阻抗建立了土壤水分探头的特征阻抗数学模型。为了获得SWR型土壤水分传感器的输入(土壤含水率)/输出(电压)静态数学模型,本文设计了土柱试验方案，并探究了传感器对土壤类型、土壤容重及土壤含盐量等的敏感程度。49538

本文选取大容量的微控制器STC12C5A60S2、四位串行液晶显示器EDM1990A、通信接口芯片MAX232、快速充电管理芯片MAX712(对镍氢电池进行智能充电)等作为核心硬件，与传感器配套使用，从而完成信息的测量、存储、显示及传送等。结果表明：该速测仪结构简单、测量便捷，便于推广应用。

毕业论文关键词：驻波原理；传感器；传输线；微控制器STC12C5A60S2

Abstract

This paper presents a soil moisture speed measuring instrument of low cost, high accuracy, good stability and strong adaptivity, based on standing-wave ratio theory. Through theoretical analysis of dielectric physics, it proposes a equivalent circuit of soil moisture dielectric measurement and the best test frequency. On this basis, it builds the structure of soil moisture transducer; And it builds the characteristic impedance mathematical model of soil moisture probe, through calculates the characteristic impedance of transmission line. In order to get the input (soil moisture content)/output (voltage)static mathematical model of soil moisture impedance, it designs soil column test plan and explores the sensitivity of transducer to soil types, soil bulk density，and soil salinity. 

The large capacity micro controller STC12C5A60S, four serial LCD monitor EDM1990A.communication interface MAX232.fast charging management chip charging management chip MAX712 (to intelligent charging the NiMH batteries) as a core part of the hardware, supporting the use of the sensor and complete information measurement, display, transmission and storage. On above, the instrument has simple structure, convenient measurement and it is easy to application. 

keywords:Standing-Wave Ratio；Transducer；Transmission Line；Micro Controller STC12C5A60S2        

目  录

第一章  绪论 1

1.1 课题研究的背景和意义 1

1.2 各种土壤水分测量方法总览 1

1.2.1 烘干法 1

1.2.2 张力计法 2

1.2.3 中子仪法 2

1.2.4 红外法 2

1.2.5 电阻法 2

1.2.6 时域反射法（TDR） 2

1.2.7 频域反射法（FDR） 3

1.2.8 驻波比法（SWR） 3

1.3 本文主要研究内容 3

第二章  SWR型土壤水分传感器的测量原理 4

2.1 引言 4

2.2 介电法测量土壤含水率的理论分析 4

2.2.1 土壤水分介电测量的等效电路 5

2.2.2 土壤水分介电测量的频域分析 7

2.2.3 确定最佳测试频率 11

2.3 基于驻波比原理的土壤水分测量法