基于频率响应特性的平行板电容式土壤湿度检测研究

发布时间：2018-03-02 09:34

本文关键词： 平行板电容频率特性土壤湿度检测　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：土壤湿度是土壤的重要物理参数之一,在整个地球上的水循环中,土壤水分是地表-大气间物质交换和能量循环过程中的关键因素。土壤湿度值影响着农业工程、深林植被、生态保护、气象预报、水文研究、灾害防护、土木工程等众多领域,因此检测土壤湿度具有重要意义。检测土壤湿度的方法很多,由于土壤本身的复杂性和测量条件的限制,各种检测方法都存在一定的局限。基于介电特性法的检测技术是目前相比其它种类方法更为广泛应用的检测手段,其原理是根据土壤的相对介电常数主要由其中的水分含量决定,通过测量土壤相对介电常数值或与其具有确定函数关系的物理量大小可以间接得到土壤湿度值。作为介电特性方法中的一种,电容法与其它方法如TDR、FDR、SWR相比具有成本低,电路简单,测量准确,便携性好,操作方便等突出优点,其探头可以适应多种土壤。因此电容法具有很大的推广价值,其核心在于检测探头与检测电路的设计以及土壤湿度与输出信号的对应关系的确定。本文对土壤介电特性进行分析研究,以电容法为原理设计了一种平行板结构的电容式土壤湿度检测装置,并进行了相关试验以验证其性能。本项研究的主要内容和研究成果主要体现在:(1)对土壤等效介电模型进行了分析,选择阻容并联电路为土壤等效电气模型。本文将传递函数的概念引入土壤等效电路的检测中,提出了基于传递函数频率响应特性的土壤湿度测量方法,该方法有效降低了测量结果容易受到输出信号自身误差影响的风险,数学模型稳定可靠、计算结果精确。(2)设计并制作了平行板电容式土壤湿度传感器装置,包括平行板探头及电路部分。平行板式结构的探头插入土壤更方便,对地面平整度要求较低,单次检测范围更大,维护保养简单。探头材料采用不锈钢,结构坚固,耐用性好,可适用于大多数质地的土壤。该装置一次最大可以检测2.5×3.5×13cm3体积范围内土壤的平均湿度。(3)本文采用无水乙醇与去离子水配比溶液和沙土作为介质进行多组试验。乙醇溶液作为土壤的等效介质可用于实验室替代土壤的材料,大大降低减少实验室标定土壤湿度传感器时采样难度,节省了实验时间。试验采用选定频率段内多组频率信号重复扫描的测试方法,根据实验数据对被测介质等效介电模型进行了验证,显示用一阶RC并联网络能较好的表示土壤介电性质。(4)理论电容值测量时平行板电容的边缘效应不能忽略,本文提出了简化的包含边缘电容在内的理论电容计算公式,并利用Cosmol软件对实验过程进行模拟,仿真所得电容值同实验结果相比呈比例相似,即两者随含水率变化的规律相似,证明了本文设计的试验装置和提出的检测方法可行性良好。针对理论电容值与测试电容值的偏差,本文提出用理论计算电容值乘以比例系数(比例系数值与介质材料有关)的方法对传感器测量结果进行标定。标定后的理论电容值与试验电容值拟合良好。该研究对开发成本低、准确度高、抗干扰能力强、可应用于户外测量的平行板电容式土壤湿度传感器有良好的参考价值。
[Abstract]:Soil moisture is one of the important physical parameters of the soil, the earth's water cycle, soil moisture is the key factor of surface atmosphere exchange of material and energy cycles. Soil moisture values affect agricultural engineering, forest vegetation, ecological protection, weather forecasting, hydrological research, disaster protection, many areas of civil engineering the project, therefore soil humidity detection has important significance. Many methods of soil humidity detection, because of the complexity of soil itself and the measurement conditions, various testing methods have some limitations. Based on the detection technology of dielectric characteristics of the method is the current detection means compared to other types of methods are more widely used, its principle is according to the relative dielectric constant of the soil moisture content mainly by the decision, by measuring the soil relative dielectric constant or its determined physical quantity function. The relationship between the size of In order to get indirect soil moisture values. As a kind of dielectric characteristic method, capacitance method and other methods such as TDR, FDR, SWR compared with low cost, simple circuit, accurate measurement, good portability, has the advantages of convenient operation, the probe can adapt to a variety of soil. So the electrical capacitance method has great popularization the value of its core lies in the detection probe and the detection circuit design and determine the relation between soil moisture and the output signal. The analysis on the soil dielectric properties in this paper, the design principle of capacitive soil moisture detection device of a parallel plate structure with capacitance method, and tested to verify its performance. The main contents and results of this study is mainly reflected in: (1) on the soil dielectric model is analyzed, selection of RC parallel circuit for soil. The concept of equivalent electrical model of the transfer function of the lead Detection in soil equivalent circuit, put forward the measurement of soil moisture transfer function method based on frequency response characteristics, the method can effectively reduce the risk measurement results are easily influenced by the output signal of its error, the mathematical model is stable and reliable, accurate calculation results. (2) the design and fabrication of the parallel plate capacitive soil moisture sensor device. The probe includes a parallel plate and a circuit part. The parallel plate structure of the probe inserted into the soil more convenient, on the surface flatness requirement is low, a single larger detection range, simple maintenance. The probe is made of stainless steel material, solid structure, good durability, can be applied to most soil texture. The device can be one of the largest detection of 2.5 * 3.5 * 13cm3 soil volume range. The average relative humidity (3) by using anhydrous ethanol and deionized water solution ratio and sand as the medium for multiple testing. Ethanol solution As the equivalent medium soil can be used to substitute the soil laboratory, greatly reduce the laboratory calibration of soil moisture sensor sampling difficulty, save the experimental time. In the experiment the selected test method frequency multiple frequency signal repeat scan, according to the verification of the measured medium dielectric model experimental data, with a display order RC parallel network can better represent the soil dielectric properties. (4) the theory of capacitance ignored edge effect of parallel plate capacitance measurement, this paper presents a simplified containing edge capacitance theory, capacitance calculation formula, and the experimental process was simulated by using Cosmol software, the simulation results compared with experimental values obtained capacitance a similar proportion of the two, with the change of water content of the similar law, to prove the feasibility of the experimental equipment and method for detecting the good in science. The capacitance value of the capacitance value and deviation test, put forward to calculate the capacitance value multiplied by proportional coefficient (proportion coefficient theory related to dielectric material method) calibration of the sensor measurement results. The theory of capacitance after calibration values agree well with the experimental values. The study on the capacitance of the development of low cost, high accuracy, anti-jamming the ability is strong, can parallel plate capacitive soil moisture sensor used in outdoor measurement has a good reference value.

【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S152.71

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