Abstract: This paper presents a multi-point remote automatic water level measurement mode based on industrial application frequency bands and GSM SMS platform. The entire system consists of three parts: measurement site, measurement front-end, and monitoring center. Multiple measurement sites transmit water level information through drop-in transmitters using a same-frequency time-series addressing encoding method, which features high receiving sensitivity, long transmission distance, strong anti-interference capability, and low investment cost. The measurement front-end collects water level data of the monitored river section in near real-time, and transmits it to the monitoring center in the form of GSM SMS after encoding for storage, query, analysis, and statistics. Keywords: remote data transmission; automatic measurement; data acquisition; wireless communication 1 Introduction Currently, China has approximately 300,000 kilometers of secondary flood control dikes, 300,000 small and medium-sized reservoirs, and 2,000 large and medium-sized drainage pumping stations. Due to bottlenecks such as instrument technology, equipment price, and funding, the hydrological information of reservoirs, river networks, and small and medium-sized reservoirs required for flood control and drainage scheduling is scarce and delayed. We developed a remote, multi-point, fully automated water level measurement system by employing submersible water level measurement, data encoding and wireless transmission, a time-series distributed access (TSA) receiving scheme, and utilizing the short message transmission platform in the GSM system, combined with a network database. This system has been successfully applied to the real-time hydrological data acquisition system for flood control and drainage in the Dongting Lake area of ​​Hunan Province, achieving large-area networked real-time hydrological data acquisition. 2. System Overall Structure and Functions of Each Component The overall system block diagram is shown in Figure 1. The entire system consists of three parts: the measurement site, the measurement front-end, and the monitoring center. The measurement site is distributed at various locations upstream and downstream of the water body, collecting water level data and transmitting it to the measurement front-end via an industrial 315MHz channel using a time-series distributed access (TSA) encoding method. The measurement front-end is distributed at various observation stations in the water body, achieving multi-point reception, storing the water level information from the measurement site, and displaying it digitally in real-time using LEDs. Simultaneously, it encodes the data in a specific way, encapsulates it according to the short message format, and sends it to the monitoring center via a GSM module. The front-end receives instructions from the monitoring center and modifies its own operating parameters. The monitoring center can set the working mode and related initialization parameters of the measurement front end, obtain the working status of the measurement front end, receive SMS data from the measurement front end, extract water level data collected at the measurement site, record the water level data in the network database, and query, statistically analyze, process, and print relevant reports. [align=center] Figure 1 Overall block diagram of the remote automatic water level measurement system[/align] 3 Design and Implementation 3.1 Implementation of measurement site functions. The block diagram of the measurement front end is shown in Figure 2: [align=center] Figure 2 Block diagram of the measurement site[/align] 3.1.1 Water level signal acquisition and processing The submersible water pressure transmitter measures the water level using a pressure conversion method. This system uses the MPX2100 diffused silicon force-sensitive piezoresistive device. The MPX2100 has temperature compensation characteristics, good linearity, and the output voltage is precisely proportional to the applied pressure. The MPX2100 converts the water level pressure into a millivolt differential voltage signal. Due to signal conditioning and output requirements, the XTR115 chip is used to operationally amplify the millivolt-level voltage output from the MPX2100 into a 1-5V standard signal voltage. Because ASK modulation is required for transmission, this voltage must undergo A/D conversion. This system uses the LM331 chip to perform the A/D (V/F) conversion, transforming the 1-5V water level voltage into a 1-5kHz frequency signal. 3.1.2 Water Level Data Encoding and Transmission: The encoding and transmission mainly consists of a PT2262 encoding IC and high-frequency modulation and power amplification circuits, as shown in Figure 2. The PT2262 is a low-power, low-cost general-purpose encoding circuit manufactured using CMOS technology. It has 12 tri-state address pins (A0-A11) (floating, high-level, low-level), which can be combined to generate an address code of 531441. The PT2262 can have up to 6 data pins (D0-D5), with the address code and data code serially output from pin 17. The PT2262 encoding chip outputs an encoded signal consisting of an address code, a data code, and a synchronization code, forming a complete codeword. Simultaneously, the corresponding data pin outputs a high level, and pin 17 outputs a modulated serial data signal. When pin 17 is high, the 315MHz high-frequency transmitting circuit oscillates and transmits a constant-amplitude high-frequency signal. When pin 17 is low, the 315MHz high-frequency transmitting circuit stops oscillating. Therefore, the high-frequency transmitting circuit is completely controlled by the digital signal output from pin 17 of the PT2262, thus performing amplitude keying (ASK modulation) on the high-frequency circuit, equivalent to 100% amplitude modulation. The effective operating distance of the encoding transmitting module can reach 3-4 km outdoors. If necessary, a repeater can be added between it and the measurement site, significantly increasing the communication distance. 3.2 Measurement Front-End Function Implementation. The measurement front-end block diagram is shown in Figure 3: [align=center] Figure 3 Measurement front-end block diagram[/align] 3.2.1 Decoding and Receiving The PT2272 uses a dual-row 18-pin connector, where A0～A5: encrypted address encoding output terminals, with the same state as A0～A5 in the PT2262. D0～D5: control data output terminals, which are six-bit binary codes, latched output. VT: decoding valid indicator terminal. When decoding is valid, the VT terminal changes from low level to high level. When a 315MHz radio signal is received, it first performs two checks. If the address matches the address encoding of the transmitting circuit, the decoding indicator terminal VT outputs 1, and at the same time, the data output terminals D0～D2 of the transmitting circuit 2262 are output in parallel to the D0～D2 terminals of the 2272 to achieve decoding output. The receiving and demodulation module and the STC89C52 microcontroller are connected together to form a multi-point to one-point open receiving system. After separating (decoding) the address and data codes of the signals from each measurement point, the multiple data streams are packaged and sent to the GSM module. The GSM module then transmits the data remotely in the form of SMS messages. 3.2.2 Wireless Digital Display Receiving: The measurement site transmits a 315MHz signal. The decoded serial pulses are sent to the STC89C52 microcontroller. The STC89C52 microcontroller reads the data in frequency counting mode, processes it, and displays it. To facilitate the conversion of the measured water level to altitude, the wireless intelligent digital display dial has initial reading and full-range setting keys for random setting. 3.2.3 SMS Sending and Receiving: This system uses the DTR2006 GSM module to realize remote data transmission. This module provides multiple data interfaces such as RS232/RS485/TTL and uses SMS service based on the GSM network, which is stable, secure, and reliable. Due to the needs of measurement work, it is required that the real-time data acquisition time be attached to the SMS message sent to the monitoring center each time. For this reason, we added a standard time generator to the design and adopted the industrial-grade high-precision real-time clock chip SD2203AP. This chip has a built-in crystal oscillator, supports I2C bus, and has an annual error of less than 2.5 minutes. 4 Monitoring Center Function Implementation 4.1 SMS Encoding and Decoding The DTR2006 GSM module has a master station and a slave station working mode. The monitoring center GSM module should be set as the master station, and the measurement front-end GSM module should be set as the slave station. Its SMS sending and receiving format is specified as follows: Fn + NUM + DCS + UDL + UD + 03 (1) Fn n is the length of the telephone number (1 Byte), usually "00001011". (2) NUM Telephone number (recipient number) (1-8 Bytes). (3) DCS encoding method (1 Byte) 00: 7-Bit ASCII code; 04: 8-Bit byte; 08: UNICODE code. (4) UDL data length (1 Byte) Value range: 01～8cH. (5) UD data (1-140 Byte), data encoding format: collection time (year, month, day, hour, minute, 5 bytes in total) + measurement site number (1 Byte) + water level data (pressure value, 2 bytes) + measurement site number (1 Byte) + water level data (pressure value, 2 bytes) + …. (6) 03 end mark (1 Byte). 4.2 Water level data storage Considering that the system collects a large amount of data, has high requirements for database performance, and has great value in preserving historical data, the large-scale network database system Oracle9i was selected and equipped with a dedicated database server. The monitoring center computer connects to the database server through the local area network where the center is located to complete the storage and retrieval of water level data. The business database construction standard adopts the "Flood Control Engineering Database Design Report" of the National Flood Control Command System Engineering, and the real-time rainfall and water information database standard adopts the "Real-time Water and Rainfall Information Database Table Structure" of the National Flood Control Command System Engineering. For fields that lack national or industry standards but are frequently used, have large data volumes, or frequently require sorting and statistics, a unified code compilation rule and code table are defined within this system. 4.3 Application Software Design We developed the application software required by the monitoring center using VC++, employing a standard Windows graphical user interface. The main functional modules include: parameter settings, permission settings, query statistics, report output, and automatic alarm functions. Due to space limitations, this section is omitted. 5. Conclusion This system adopts a remote data acquisition scheme based on wireless and SMS platforms, possessing advantages such as advanced technology, high accuracy, high automation, low cost, convenient installation, simple use, and adaptability to harsh outdoor environments. The system has been verified by the Hunan Provincial Institute of Metrology and Testing, achieving a comprehensive measurement accuracy of 1‰. Under the legally permitted wireless transmission power, the effective transmission distance can reach 2km. The product has been used in multiple drainage pumping stations in the Dongting Lake area of ​​Hunan Province with good results. The author's innovations: 1. To reduce project costs, a wireless connection is used between the data acquisition site and the measurement front end, with data and instructions transmitted remotely and automatically via SMS. 2. To facilitate widespread application, the measurement front-end requires no computer (PC) support and is fully unattended. 3. To reduce investment, the data front-end can wirelessly receive data from multiple locations and display it digitally, making installation and use extremely convenient. 4. To achieve economical system operation: A. Multiple sets of data are bundled and sent; B. The data acquisition interval can be set by the monitoring center. References: [1] Shen Zhaojun, Mao Min. Realization of smart home using GSM SMS service [J]. Microcomputer Information, 2006, 22 (1-3): 211-213 [2] Yuan Tianyou, Xie Yue. Design and implementation of remote residential intelligent monitoring system based on GSM [J]. Microcomputer Information, 2006, 22 (5-1): 95-96 [3] Wang Qiben, Liu Jingao. 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