不同频率激励信号下土壤水分传感器性能试验

激励信号频率是影响高频电容式土壤水分传感器性能的重要因素。利用去离子水和2—异丙氧基乙醇(2—isoproxyethanol)或二氧六环(dioxane)2种溶液混合,配制了一系列等效土壤体积含水率为0.9%~51.8%的待测介电溶液来替代土样。从与土壤含水率的函数关系、温度变异性2个方面,分别对激励信号频率为40,50,60,70,80,90,100 MHz的7种土壤水分传感器进行了性能测试与分析。结果表明:7种频率的传感器的输出电压均与土壤体积含水率呈线性负相关,其相关系数R2均大于0.94;激励信号频率不影响传感器输出电压的温度变异性,温差是影响温度变异性的主要因素,其最大变异率均小于4%。试验结果可为设计高频电容式土壤水分传感器时选择激励信号频率提供依据。

Performance experiments of soil water content sensor in different frequency of excitation signal

The frequency of excitation signal is an important factor that affects performance of high-frequency capacitive soil moisture sensor. A series of tested dielectric solution whose equivalent soil volumetric water content is 0.9 %-51.8 % ,is prepared by deionized water mixing with 2-isoproxyethanol or dioxane, instead of soil sample to test performance of soil water content sensor. Performance test and analysis are carried out from two aspects which are the relationship with soil water content and temperature variability with seven sensors whose excitation frequency is 40,50,60,70,80,90,100 MHzl The results show that the output voltage of seven kinds of frequency of sensor has linear negative correlation with volumetric soil moisture, and the coefficient of correlation R2 is greater than 0.94, and the temperature variability of output voltage of the sensors is not affected by excitation signal frequency, the temperature difference is the main factor that affects temperature variability, and the maximum variation is less than 4 %. The test results can provide guidance for choosing the frequency of excitation signal when designing a high-frequency capacitive soil water content sensor.