自动双环入渗仪设计与试验

为克服传统双环入渗仪的供水不稳定、读取和记录数据工作量大的问题,该文基于定水头法测量导水率的原理,设计了一种高效的自动双环入渗仪。该入渗仪采用非接触式电容感应液位传感器来监测内环和外环内的水位(精度<1.5mm);将激光测距传感器(精度<1mm)安装在圆柱形蓄水器的顶部,以连续自动监测供水量;高精度液位控制系统与电磁阀组合以保持恒定水头。通过理论分析,增大蓄水器中的液面与双环中的液面之间的压力差,可使自动双环入渗仪的初始供水速率远高于马氏瓶的初始供水速率。自动双环入渗仪的精度和可靠性试验于2019年7月至2019年10月在中国农业大学绿苑试验场进行,并进行了该自动双环入渗仪和传统双环入渗仪之间的比较。试验结果显示,在选定土壤的稳定入渗阶段,用马氏瓶测量的稳定入渗速率为0.0685 cm/min,该自动双环入渗仪的稳定入渗速率为0.0687 cm/min,自动双环入渗仪实测数据与Philip的理论入渗模型计算结果吻合(R^2>0.99)。结果表明,该自动双环入渗仪的自动化测量结果可靠,对今后土壤水分入渗过程研究提供了更加高效的手段。

Design and experiment of automatic double-ring infiltrometer

Double-ring infiltrationmeter is widely used to combine with the Mariotte bottle for measuring soil hydraulic conductivity. However, there are various kinds of measurement error and shortcomings using the traditional double-ring infiltrometer, particularly on unstable water supply, high labor intense when reading and recording of data. In this study, a new automatic double-ring infiltration meter was designed to improve the measurement precision, while reduce various sorts of errors. A fixed water level method was develop a low-cost and efficient automatic double-ring infiltration meter according to the measuring theory of hydraulic conductivity. The new-developed double-ring infiltrometer was mainly composed of inner (diameter of 17.6 cm) and outer rings(diameter of 30 cm), non-contact liquid induction capacitor level sensor (accuracy <1.5 mm), cylindrical water container, laser ranging sensor module (accuracy <1 mm), solenoid valve and other components. A non-contact capacitor induction liquid level sensor was selected for monitoring the water level, in order to keep the water level constant inside the both inner and outer ring. A cylindrical water reservoir was served as water source for the container of infiltration meter, and a sensor module with laser ranging was installed on the top cover of the reservoir. A laptop was connected the laser ranging sensor module to automatically monitor the volume of water supplied continuously. The combination of the high-precision liquid level control system with the non-contact inductive capacitive liquid level sensor and solenoid valves can be used to maintain a fixed water level in the water reservoir. Therefore, it is possible to increase the pressure difference of liquid level between the water reservoir and the double-ring, and thereby to make the initial rate of water supply in the double-ring infiltration meter much higher than that in the Mariotte reservoir. The new infiltration meter can match the initial rate of water supply, thereby to improve the measuring accuracy of hydraulic conductivity. The accuracy and reliability of the automatic double-ring infiltration meter were verified from July 2019 to October 2019, in the Lvyuan experiment field of China Agricultural University. The experiment was also performed on comparison between the new infiltration meter and the traditional infiltration meter with fixed water level method (double-ring combined with the Mariotte reservoir, collecting data manually). The field experiment results demonstrated that, the stable hydraulic conductivity measured by the Mariotte reservoir was 0.0685 cm min-1, and the stable hydraulic conductivity measured by our new automatic double-ring infiltration meter was 0.0687 cm min-1. The data measured by new designed double-ring infiltration meter agreed with the theoretical infiltration model of Philip, where the corresponding R2 was greater than 0.99. In addition, the new double-ring infiltration meter can continuously and automatically measure the infiltration process, which significantly reduced error caused by traditional double-ring infiltration meter. The new infiltration measurement system can be expected to extend for automatic data sampling with high precision, and low cost, efficient, and easy to use in the field.