针对大型称重式蒸渗仪测控系统常见的缺乏通用性、扩展性不足和可靠性差等问题，该文提出了一种基于LabVIEW和ARM处理器的分布式大型称重式蒸渗仪测控系统。底层测控单元全部采用ARM处理器LPC1768开发设计，所有单元均通过RS485方式MODBUS协议与上位机进行通信，上位机测控软件采用LabVIEW设计开发，支持对除称重参数以外的其它测量参数的选择。同时采取了中值滤波和滑动窗口平均滤波等信号处理算法，提高称重测量精度。运行试验表明，在称重分辨率达到0.1 g，杠杆系数为277.7时，蒸发量或降雨量的分辨率达到了0.0072 mm水深。%With the great developments of agricultural productions and concerned research projects needs in China, the use of direct methods using lysimeters for measuring water and solute flow in soils has increased in recent years. Large weighable lysimeters were best suitable for obtaining reliable data about seepage water quantity and quality. The field lysimeters combined the advantages of true field conditions and laboratory possibilities of varying parameters, handling and maintenance. Instrumentation varied due to the specific needs of each application. In order to provide a unified software and hardware platforms and system configuration scheme for the automatic measuring and controlling lysimeters, a new method using the LabVIEW and ARM processors was proposed in this paper. The systems proposed consisted of three sections:the tank holding the main soil body, the weighing and load control system, the supervisory control and data acquisition system. The weighing and load control system, which were the core parts in the lysimeter, consisted of a precise electric balance with high resolution, multi-stage lever systems and an intelligent load control system. The balance, with resolution up to 0.1 g, connected with the host computer by RS232 bi-directional interface. To improve the reliability and accuracy of weighing system further, an intelligent load control system was developed based on the LPC1768 MCU, which communicated with the host computer via the RS485 interface. The supervisory control and data acquisition system mainly consisted of the data acquisition units, the communication module and the host computer. Also the data acquisition units controlling the digital sensors were developed based on the LPC1768 MCU. In the whole monitoring system, theses data acquisition units functioned as the bottom nodes, which receiving commands from the host computer, collecting sampled data from various sensors and sending data back to the host computer in real time. Considering the reliability of the measuring system, advanced digital sensors from Decagon were selected in this system, which could measure the soil’s temperature, water content, electric conductivity (EC), water potential, etc. These digital sensors with very low power requirements and excellent specifications, connected with the data acquisition units by RS232 interface with 150ms measurement time. Meanwhile, the host computer controlled these data acquisition units via RS485 communication interfaces adopting MODBUS protocol. So under this working mode, theses intelligent units worked in the RTU mode. The measurement system of the seepage and the control system of the drainage were also designed based on the LPC1768 MCU, which connected with the host computer via the RS485 communication interfaces. Considering the actual needs of remote monitoring, a flexible and economical GPRS module with RS485 interface was adopted to let the host computer report its state periodically to the operators via short message. The host computer system consisted of an industrial personal computer and the measure–control software which was developed with LabVIEW and had characteristic of the friendly human-computer interface. In this software, the sensor’s type, quantity and sampling parameters could be configured. Meanwhile, flexible signal processing algorithms,including timed loop technique, moving averaging and median filter, were adopt to improve the accuracy further. Under this two-stage structure, the host computer controlled the whole systems, the data could be displayed and analyzed in real-time. The experimental results showed that the resolution of the Lysimeters was up to 0.0072mm.
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