Specifications

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.
Number of references: 28
Main heading: Soil surveys
Controlled terms: ARM processors - Communication - Computer programming
languages - Computer software - Control systems - Data acquisition -
Evapotranspiration - Interface states - Lysimeters - Measurements - Seepage -
Sensors - Signal processing - Soils - Water supply - Weighing