电容式土壤水分传感器的电导变异性试验研究

为评估电容式土壤水分传感器受土壤电导率的影响及其对农田土壤电导率变化范围的适用性,配制了一系列土壤等效含水率为40.6%、电导率为0~1.91dS/m的土壤等效介电溶液,分别对激励信号频率为40,50,60,70,80,90,100MHz的7种传感器进行了电导变异性试验,并且配制了相同含水率但电导率分别为0,0.31,0.46和0.61dS/m的4种土样进行了验证试验。试验结果表明:1)土样中的测试结果基本上与介电溶液吻合,可采用等效介电溶液评估传感器的电导变异性;2)传感器的电导变异率随待测介质电导率的升高而近似线性增大,相同电导率下,传感器激励信号频率越高其电导变异率越小;3)在农田土壤电导率基本变化区域0.239~0.650 dS/m内,当传感器激励信号频率从不低于80MHz时,其最大电导变异率为9.2%,能满足工程上的实际应用要求。

Experimental study of capacitive soil conductance variability of moisture sensor

In order to evaluate influence of soil conductivity on capacitive soil moisture sensor and applicability of sensor to variation range of agricultural soil, a series of soil equivalent dielectric solutions whose soil equivalent water content is 40.6 % and conductivity is at the range of 0 - 1.91 dS/m is prepared, and experiments of variability conductance on seven kinds of sensors whose excitation signal frequency of 40,50,60,70,80,90 and 100 MHz are performed by using the prepared equivalent dielectric solutions, and then four kinds of soil samples whose moisture content is 40.6% and soil conductivity of 0,0.31,0.46 and 0.61 dS/m respectively are prepared to verify the results tested in equivalent dielectric solutions. Test results show that 1 ） test results in soil samples are basically in accordance with that in the equivalent dielectric solutions, so it can employ equivalent dielectric solutions to assess variability for conductivity of sensor; 2 ） variation rate for conductivity of sensor has an approximately linear increase with rising of conductivity of the tested medium, and the higher the frequency of excitation signal of sensor is the smaller variation rate for conductivity of sensor is in the tested medium of same conductivity ; 3） maximum variation rate for conductivity of sensor is 9.2 % , when its excitation signal frequency is not less than 80 MHz at the range of 0. 239 ~ 0. 650 dS/m, which is the basic conductivity variation range of agricultural soil, which can meet the requirements of engineering application.