基于无线传感器网络的温室栽培营养液电导率监测系统

温室营养液无土栽培,具有节约种植成本、生产效率高等优点.监测营养液的电导率、pH值等特性参数,是实现营养液无土栽培信息化与自动化的基础.为了实现温室无土栽培营养液的实时监测,开发了基于无线传感器网络(wireless sensor network, WSN)的营养液电导率实时监测系统.系统以JN5139为中央控制器同时控制营养液电导率信息采集单元和无线通讯单元,实现了营养液电导率信息的实时采集与处理、LCD显示和键盘输入等人机交互操作以及基于WSN的营养液电导率实时测量自组织网络,同时系统集成了GPRS模块,实现了营养液电导率与温度信息的远程传输与监控等功能.系统采用星型网络拓扑结构,并进行定时休眠、传感器掉电控制来节省能源消耗.针对系统的实用性和可靠性进行了系统标定、温度补偿以及温室试验,分析比较了电导率测量线性与非线性模型.试验结果表明分段线性模型建模效果较好,分段拟合R2均在0.97以上.系统的测量范围为0.5~2.9 mS/cm,测量结果能够精确到0.01 mS/cm,总体测量相对误差为2.10%,较好地满足了温室营养液电导率实时监测的要求,为无土栽培的科学管理提供技术手段.

Monitoring system for electrical conductivity of greenhouse nutrient solutions based on WSN

The application of hydroponics and a substrate-based culture in a greenhouse has been paid much attention to by more and more people for its environmental protection and high efficiency in the production. In order to promote automation of the soilless culture in a greenhouse, it is necessary to monitor the electrical conductivity (EC) of the nutrient solution used in greenhouse. Therefore, a monitoring system for EC of the nutrient solution in a greenhouse based on WSN was developed. The system consisted of a measurement section, a transmission control section, and a terminal server. The measurement section, including a conductivity electrode (DJS-1C) and a digital temperature sensor (DS18B20), could measure the EC and temperature of nutrient solution and then send the data to the transmission control section. The transmission control section could collect and process the data from different sensor nodes, and then display the result on the LCD screen to satisfy the needs of human-device interaction. It could also transmit the data of EC and temperature to the terminal server. The core controller of the whole system was a JN5139 module, which was responsible for collecting data in the measurement section, connecting with a GPRS module in the transmission control section through serial ports, and controlling GPRS by using AT commands. In this way, the system realized the remote transmission and management of soilless culture information. The data transmission was performed based on the IEEE802.15.4 standard and TCP/IP protocol. To save the consumption of power, the system was developed in a star network topology, combining with regular sleep and switches of the power of information collecting modules. Calibration tests were done in the laboratory to verify the accuracy of the system. Several estimation models were built and verified such as Piecewise linear model, Power function model, Logarithmic model, and Polynomial model. The results showed that the Piecewise linear model was the best choice, and the R2 for fitting was greater than 0.97. In addition, experiments in greenhouse were conducted from June, 2012 to July, 2012 to monitor the EC of the nutrient solution of tomatoes. The precision reached to 0.01 mS/cm with a relative error of 2.10% and the range of the measurement was from 0.5 mS/cm up to 2.9 mS/cm. It was proved that the system could satisfy the requirements of real-time EC measurement in greenhouse.