Monitoring system of subsurface pipe drainage for improving saline-alkaline soil based on wireless sensor network

Abstract: Soil salinization is a serious environment problem. The subsurface pipe drainage technology is a physical method used to reduce soil salinity in the coastal saline regions. At present, there is a problem that the application effect of subsurface pipe drainage technology is difficult to be evaluated because of the lack of scientific experimental data. In order to solve the problem, a monitoring system of water quality of drainage water was provided based on wireless sensor network to obtain the water quality information on line. The system mainly consisted of 9 sensor nodes, a control node and a central node. The water sensor node was composed of a water conductive sensor, pH sensor, flow meter, power module and wireless network connection module. The control node was used to drive the relay to control the water pump. The sensor nodes of the system could collect information of water conductivity, pH value and pipe drainage flow and send the data to center node. The center node sent the data to computer by RS232 interface. Meanwhile, the information of water level of reservoir was collected on line by using the level sensor and sent to the center node through the wireless transmission module. In order to improve the water level measurement accuracy, the first order inertial filtering algorithm was adopted. The control decision was made based on the acquired water level information and sent to the control node to realize the remote control of the water level of the reservoir. The desired level of reservoir is set at point. At the same time, the upper layer test software was developed based on Labwindows/CVI. The advantages of this software were presented by the process of modular design, including parameters setup, water quality and flow information acquisition and processing, parameter curves real-time display, data storage and replay. The outdoor monitoring nodes were using solar power. In order to obtain an optimal capacity of the solar cell array and lead-acid battery, photovoltaic capacity of the power system was designed. In order to verify the overall performance of the system, practical application experiment for the monitoring system had been taken for more than 8 months. Firstly, the water level control experiments were carried out, and the experiment results showed that the reservoir water level was well controlled between the upper and lower limits. The water quality measurement results showed that the sensors had the high accuracy, and the relative errors of pH value and conductivity were less than 1.81% and 1.89%, respectively. At the same time, the influence of transmission distance and packet loss was studied. According to the experiment data, when the distance exceeded 125 m, the packet loss rate increased significantly. The experiment results provided an effective reference for the layout of wireless nodes. We also tested the communication performance of the whole system, and the maximum relative error of packet loss was less than 2.6%. The system can accurately obtain the information of the water quality and migration change in the alkali dark pipe, and provide favorable data support for the evaluation of the effect of subsurface pipe drainage technology.