本文關鍵詞： 平行板電容 頻率特性 土壤濕度 檢測　出處：《太原理工大學》2017年碩士論文　論文類型：學位論文

【摘要】：土壤濕度是土壤的重要物理參數(shù)之一,在整個地球上的水循環(huán)中,土壤水分是地表-大氣間物質交換和能量循環(huán)過程中的關鍵因素。土壤濕度值影響著農業(yè)工程、深林植被、生態(tài)保護、氣象預報、水文研究、災害防護、土木工程等眾多領域,因此檢測土壤濕度具有重要意義。檢測土壤濕度的方法很多,由于土壤本身的復雜性和測量條件的限制,各種檢測方法都存在一定的局限。基于介電特性法的檢測技術是目前相比其它種類方法更為廣泛應用的檢測手段,其原理是根據(jù)土壤的相對介電常數(shù)主要由其中的水分含量決定,通過測量土壤相對介電常數(shù)值或與其具有確定函數(shù)關系的物理量大小可以間接得到土壤濕度值。作為介電特性方法中的一種,電容法與其它方法如TDR、FDR、SWR相比具有成本低,電路簡單,測量準確,便攜性好,操作方便等突出優(yōu)點,其探頭可以適應多種土壤。因此電容法具有很大的推廣價值,其核心在于檢測探頭與檢測電路的設計以及土壤濕度與輸出信號的對應關系的確定。本文對土壤介電特性進行分析研究,以電容法為原理設計了一種平行板結構的電容式土壤濕度檢測裝置,并進行了相關試驗以驗證其性能。本項研究的主要內容和研究成果主要體現(xiàn)在:(1)對土壤等效介電模型進行了分析,選擇阻容并聯(lián)電路為土壤等效電氣模型。本文將傳遞函數(shù)的概念引入土壤等效電路的檢測中,提出了基于傳遞函數(shù)頻率響應特性的土壤濕度測量方法,該方法有效降低了測量結果容易受到輸出信號自身誤差影響的風險,數(shù)學模型穩(wěn)定可靠、計算結果精確。(2)設計并制作了平行板電容式土壤濕度傳感器裝置,包括平行板探頭及電路部分。平行板式結構的探頭插入土壤更方便,對地面平整度要求較低,單次檢測范圍更大,維護保養(yǎng)簡單。探頭材料采用不銹鋼,結構堅固,耐用性好,可適用于大多數(shù)質地的土壤。該裝置一次最大可以檢測2.5×3.5×13cm3體積范圍內土壤的平均濕度。(3)本文采用無水乙醇與去離子水配比溶液和沙土作為介質進行多組試驗。乙醇溶液作為土壤的等效介質可用于實驗室替代土壤的材料,大大降低減少實驗室標定土壤濕度傳感器時采樣難度,節(jié)省了實驗時間。試驗采用選定頻率段內多組頻率信號重復掃描的測試方法,根據(jù)實驗數(shù)據(jù)對被測介質等效介電模型進行了驗證,顯示用一階RC并聯(lián)網絡能較好的表示土壤介電性質。(4)理論電容值測量時平行板電容的邊緣效應不能忽略,本文提出了簡化的包含邊緣電容在內的理論電容計算公式,并利用Cosmol軟件對實驗過程進行模擬,仿真所得電容值同實驗結果相比呈比例相似,即兩者隨含水率變化的規(guī)律相似,證明了本文設計的試驗裝置和提出的檢測方法可行性良好。針對理論電容值與測試電容值的偏差,本文提出用理論計算電容值乘以比例系數(shù)(比例系數(shù)值與介質材料有關)的方法對傳感器測量結果進行標定。標定后的理論電容值與試驗電容值擬合良好。該研究對開發(fā)成本低、準確度高、抗干擾能力強、可應用于戶外測量的平行板電容式土壤濕度傳感器有良好的參考價值。
[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.

【學位授予單位】：太原理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：S152.71

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