Design of a remote monitoring system for hydrological information based on GPRS

　　0 Introduction

　　Hydrological information is an important indicator for measuring water resources. The change of groundwater level is closely related to the amount of groundwater extraction and ground subsidence, which is of great significance for controlling ground subsidence. Traditional hydrological monitoring mainly relies on manual and semi-manual monitoring methods, resulting in problems such as heavy workload, low efficiency, complicated and error-prone data processing, and poor timeliness of information transmission. It is neither adapted to the development of informatization nor able to meet the needs of modern management. In addition, the labor intensity is also very high, and the measurement accuracy cannot be guaranteed, especially when monitoring some remote or scattered monitoring points, the work is more difficult.

　　In order to rationally utilize water resources, fully understand the status of water resources in each river basin, realize the automated monitoring and remote management of hydrological information, and rationally utilize computer technology, high-precision measuring instruments, public communication platforms and other tools, it is of great significance to realize remote real-time synchronous dynamic monitoring of hydrological information.

　　With the development of wireless communication technology, my country's informatization process is constantly advancing, and all walks of life have higher and higher requirements for informatization. In terms of the understanding of informatization, it has been upgraded from the previous simple digitization to the unity of digitization, networking and wireless. Compared with the current requirements of informatization, although the original wired system has basically completed digitization and networking, its complex wiring and high maintenance costs make it impossible to popularize and promote network nodes on a large scale, which has greatly restricted the in-depth and development of informatization. Therefore, the demand for wireless data transmission technology in informatization is increasing. Nowadays, the mobile network has a wide coverage, and the various data services it provides enable many smart devices and instruments to realize remote transmission of wireless data. GPRS, the general system wireless service, has high reliability and relatively low charges. In addition, the system based on GPRS can effectively simplify the ground facilities of the monitoring system.

　　Therefore, using GPRS as a communication medium is an effective way to realize a dynamic monitoring system of hydrological information.

　　To realize large-scale automatic monitoring of hydrological information, two problems need to be solved:

　　(1) How to accurately measure water level information in harsh environments;

　　(2) Find a data communication method that can be used in remote areas with sparse populations as well as in densely populated cities with complex building conditions for long-distance and real-time data communication, which is low-cost, easy to promote and manage through computer networks.

　　The design of the wireless remote monitoring system for hydrological information based on the GPRS network can realize automated monitoring, greatly improve the level and quality of groundwater dynamic monitoring, and lay a solid foundation for the scientific and rational development and utilization of water resources and the protection of the ecological environment. Through the application of the system, it provides necessary decision-making support and diversified services for urban sustainable development and disaster reduction and prevention.

　　1 Overall structure and working process of the system solution

　　The system uses GPRS communication, with embedded single-chip control technology and GPRS wireless module communication as the core, and transmits data to the user terminal of the monitoring center after data collection and processing, to achieve real-time dynamic monitoring of water level. The system is divided into three parts: intelligent information collection terminal, information comprehensive server and user terminal.

　　The overall structural diagram of the scheme is shown in Figure 1.

　　The intelligent information collection terminal in Figure 1 consists of a single-chip microcomputer, a GPRS wireless module, a sensor, a transmitter, etc. It is mainly responsible for collecting water level information and sending it to the information comprehensive server; the information comprehensive server is mainly divided into three modules: data reception and transmission, control management, and terminal processing, which are used to receive, process, store and display data; the user terminal includes a computer user terminal and a GPRS mobile phone user terminal. Users who use computer terminals need to install terminal applications on their computers, and then they can go online to view detailed water level data stored in the information comprehensive server; mobile phone users can obtain real-time hydrological information through their mobile phones after obtaining authorization.

　　The working process of the system is as follows: the information collection terminal collects the on-site water level data, uses sensors and transmitters to convert the data into standard signals, and then converts them into digital signals through analog-to-digital converters (A/D). The main control program of the single-chip microcomputer and the data sending subroutine send the collected data through the GPRS modem in the form of short messages. After receiving the data-encoded short message from the collection terminal, the information comprehensive server processes the water level elevation and related information, and stores it in the database for user reference. Once the user needs it, the transceiver module can be started, and the water level information and related information in the database will be sent to the user terminal.

　　The basic functions of the system are as follows:

　　(1) Automatically collect and store water level data at regular intervals;

　　(2) Manual entry of basic data and editing and modification of related data;

　　(3) Conduct statistical analysis on the collected data and prepare tables and graphs;

　　(4) Using computers and special software, the observation substation can be directly set up, debugged and monitored through the mobile phone text messaging function provided by the GPRS system;

　　(5) Capable of remote data transmission.

　　2 Design of Intelligent Information Collection Terminal

　　2.1 Intelligent Information Collection Terminal Hardware

　　The hardware of the intelligent information collection terminal is mainly composed of a liquid level transmitter, a temperature transmitter, a connecting cable and a hydrological information intelligent monitoring instrument, as shown in Figure 2. [page]

　　The scheme design adopts corrosion-resistant submersible level transmitter and platinum resistance temperature transmitter. The front end of the transmitter adopts a stainless steel shell to prevent interference from impurities in the water in the observation well. The connecting cable refers to the cable connecting the transmitter and the hydrological information intelligent monitoring instrument. Since the liquid level measurement adopts the pressure comparison form, the connecting cable adopts a special cable with a ventilation duct in the center. The hydrological information intelligent monitoring instrument is based on a single-chip microcomputer, with analog-to-digital conversion, clock chip, data storage, data display, backup power supply and other parts.

　　The working principle of the observation substation is as follows: the measured liquid level and temperature variables are converted into standardized output signals that can be transmitted using the liquid level and temperature transmitters dispersedly set at the observation points. The system uses a 4~20 mA current signal transmission method to send the signal to the information acquisition terminal. The analog-to-digital conversion part converts the analog signal into a digital signal to reduce signal attenuation and wiring complexity, and then the converted digital signal is analyzed and processed by the single-chip microcomputer. The data storage part uses a large-capacity storage chip to store the processed data.

　　The calendar clock has a real-time clock counting function and can also provide accurate date and clock signals for the monitor. The data display part displays real-time monitoring data on site. Finally, the data communication module uses its built-in modem to realize data exchange between the on-site monitor and the computer of the central monitoring station of water affairs departments at all levels. The backup power supply part can ensure the normal use of the monitor when the mains power cannot be provided normally, and the backup power supply can automatically switch with the mains power.

　　2.2 Intelligent Information Collection Terminal Software Process

　　Filtering can filter out specific frequency bands in the signal, which is an important measure to suppress and prevent interference. Based on the advantages of digital filtering, such as high precision, strong reliability, programmable change characteristics and easy integration, this system uses digital filtering to improve the authenticity of water level sampling signals.

　　When measuring water level, the impact of waves in rivers, lakes and reservoirs may cause instantaneous pulse interference with large amplitude in the sampling signal. Once such interference occurs at the sampling time, the system cannot work normally, so it is necessary to filter the sampled data. The intelligent information collection terminal adopts the median filtering method, that is, an odd number of data is taken out from the sampling window for sorting, and the sorted median is used to replace the data to be processed. The system software program arranges "redundant instructions" to enable the program to quickly return to the right track when the PC fails due to interference, the program deviates from the normal track, and "flies randomly". It also arranges "software traps" to play a role when the flying program enters the non-program area or the table area and the redundant instructions cannot be used to put the program on track. The data acquisition extension software includes a main program and a data transmission subroutine. The data transmission subroutine flow is shown in Figure 3.

　　The intelligent information collection terminal software is written in C++ language and uses the programming framework of object-oriented programming to build the main functional components of the application software in the form of components to improve the visibility of the system and facilitate data aggregation and data exchange. The Microsoft Access database is used to save and process data to improve the reliability and operation efficiency of the system.

　　3 Design of Information Integration Server Program

　　The hydrological remote monitoring network system is mainly composed of a central monitoring station and field observation substations, which are divided into two levels of networking. It consists of three links: field data collection and storage, remote data transmission, and data analysis and database management, as shown in Figure 4.

　　The hydrological information telemetry management system is written in C++ language, and has completed a modular overall design from top to bottom. The system integrates the real-time collection, preprocessing, data storage and management functions of water level information, forming an integrated comprehensive information platform. Through wireless remote transmission technology, the water resource information of the monitoring point is obtained in real time, and the data is stored in the database in different time periods according to the day, month and year. The curve (see Figure 5) is drawn to compare and analyze the data with the histogram, and the results are finally displayed to the user, and reports can be automatically generated according to user needs. The functions of the upper computer software management system are mainly composed of information comprehensive management module, real-time remote monitoring module, water resource decision support system, output module and other auxiliary function groups. [page]

　　3.1 Real-time remote monitoring module

　　The real-time remote monitoring system uses wireless data transmission technology and serial communication technology to collect data information. It can monitor the operation of the monitoring point at any time and collect water level and water temperature data in real time. The water level and water temperature sensors at the monitoring point convert the two physical quantities of water level and water temperature into analog electrical signals and transmit them to the measuring instrument. The analog signals are converted into digital signals through A/D for data processing and storage. When water resource information is needed, the user terminal can send the data to the connected modem according to the specified communication protocol, and then use the GPRS network to send the data in the form of text messages.

　　After the modem of the monitoring center receives the text message, it transmits the received data to the connected host PC through the serial port. When the monitoring center needs to collect real-time data, it can send information to the monitoring station through the real-time data collection module of the telemetry management system.

　　3.2 Water Resources Decision Support System

　　The system uses information fusion technology to analyze and comprehensively process the observation information of multiple sensors. Based on the collected information, the system searches and calculates the maximum, minimum, and average water level data of each measuring point in each year and month in the water resources database to establish a model. Combined with the water environment conditions at the time, the status of regional development, and the requirements of the overall plan, the model is used to comprehensively process and comprehensively analyze the data.

　　3.3 Output Module

　　In this section, users can import data into Excel or Word for review or further processing, and automatically generate electronic reports in the format of their own needs, including one-day, three-day and five-day reports, which can be printed out by printer.

　　4. Functional expansion and innovation of the system

　　At present, the system is only used to monitor water level, but its monitoring terminal provides a multi-channel analog input interface, which can realize the simultaneous access of multiple signals. That is, while monitoring the water level, the water temperature, flow rate, etc. are measured. The system can realize the remote transmission of data and is not restricted by environmental conditions. It can not only be used for remote monitoring of water level, but also for remote monitoring of water level of reservoir dams, river canals, reservoirs, etc. The system conforms to the development trend of the combination of GPRS technology and embedded system technology in the monitoring field. It is easy to use, simple in structure, easy to operate, and has broad application prospects.

　　5 Conclusion

　　With the progress of informatization, the hydrological information monitoring system tends to develop in a networked and technological way, requiring the acquisition of hydrological information to be more accurate and timely, and the number of hydrological observation items and contents is also increasing, which puts forward higher and higher requirements on the research and development and application of observation means and methods and hydrological monitoring technology. The hydrological information wireless remote monitoring system based on GPRS designed in this scheme is a remote data acquisition system developed by single-chip microcomputer module based on GPRS network (implemented by adding GGSN and SGSN to the existing GSM network) using short messages. The combination of long-distance data collection and GPRS wireless data transmission technology has changed the limitations of previous wired networks, and can realize the unattended function of hydrological stations, changing the low accuracy caused by previous manual monitoring. The system has a simple structure, is easy to expand, has a wide network coverage, is not restricted by geographical location, has low communication costs, and has real-time online data. It can be widely used in geology, hydrology and other fields, and can be applied to remote areas with inconvenient transportation and no electricity, and has high application and promotion value.