29-03-2012, 03:26 PM
Remote real-time monitoring soil water potential system based on GSM
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INTRODUCTION
With the development of the planting area in Xinjiang, the
crop needs a great deal of water to grow. Water source
shortage is 38.6 × 10 m3 every year (Yi Q et al., 2002). In
general speaking, the efficiency of using the irrigation water
is still quite lower in China, average about 0.4 (Honglie,
2002). Faced to the situation, we should develop the
precise irrigation.
In 1996, drip technology under membrane was firstly
introduced and applied in Xinjiang. It was very critical for
crop manager (Fuyu et al., 1999; Fuyu and Yisui, 2002).
In 2001, the automatic control management system was
introduced from Australia and used to irrigate crop in Xinjiang
(Fuyu et al., 2004). Following, some irrigation control
management systems were developed in China
(Xiuzhen et al., 2006; Li et al., 2006).
Basic structures of an information system
The information system (Figure 1) may realize a series of
functions including collecting, transporting, storing, centralization
management, statistical analysis, forecast and
browning of soil water potential data. Making the classification
according to the function, the system is composed
of monitoring center, data transmission channel and
data detection terminal.
Design of information system
Module of application software
The monitoring software is developed by visual-c language
and access database. It mainly includes several
modules, which are short message processing module,
remote communication processing module, instruction
processing module, Modbus agreement processing module,
task arrangement module and system error processing
module. As follows, make a briefly explanation for
the function of these modules.
Data collecting and management
Data is collected by three pathways in the information
system. The first pathway according to the feature and
request for the parameters measured by the meter, the
data is automatically input into the software at the timeboxed
everyday. For example, soil water potential data is
input into the information system at am 9:00 daily.
Data signal transmission
The electrical cable of four cores connects the measuring
station with pressure resistance sensor. The measuring
station is composed of multi-way switch array controlled
by program, constant current source, isolation amplifier
and 12 bites A/D converter. The sensor is periodical cycle
detected by the station system, which is actuated by the
application program in the computer. Output signal is sent
to isolation amplifier by multi-way switch array, weak signal
measured is amplified. The output range of signal volt
is between -5 to 5V. The signal volt is transformed into 12
bites numerical signal by A/D converter, which is collected,
treated, analyzed and stored in the memory by the
computer. The result measured can be showed and duplicated
by the form or curve form.