Design and Implementation of Data Collection Wireless Transmission Management System for Water Meters

Figure 1 System networking mode

This project adopts NH719-1 digital radio station, adopts advanced frequency synthesis technology, CPU phase-locked loop control, and cooperates with modems to provide transparent transmission of voice or data signals, adapting to various point-to-point, point-to-multipoint wireless data communication methods. , With the characteristics of transceiver, easy installation, easy to use, cost-effective, stable and reliable, etc., widely used in a variety of remote data acquisition and control systems.

The Radio Administration Bureau of the Ministry of Information Industry has dedicated 223~235MHz wireless data communication dedicated frequency bands to the SCADA system. According to this NH719-1 digital radio operating frequency selected 230MHz (220 ~ 240MHz adjustable), the maximum transmission power of 25W, can support RS232 and RS485 communication interface, the transmission rate adjustable (1200/2400/4800/9600b/s).

The system master station is located in the central control room. The radio station of the system master station is responsible for receiving field data from each substation. Then through the workstation RS232 serial port to transmit data to the upper system, the upper system for data storage analysis. The system has a total of 50 sub-stations, distributed in various water use. The substation's wireless data radio station is responsible for receiving real-time data collected by the electromagnetic flowmeter and sending the data to the wireless data radio station of the main station.

2.2 Communication protocol System master and slave station communication adopts the master-slave scan type communication protocol, each time the communication process is initiated by the host computer, then the slave machine responds, returns the stipulated information, completes a communication process. The information sent by the master to the slave consists of 4 bytes. The first byte is the start code (0x2A), the second byte is the slave address, and its encoding: 0~127 (the highest bit is defined otherwise). 3 bytes is the data classification command, and the 4th byte is the end code (0x2E). After the slave receives the host command information, it sends back the measurement data according to the command. The slave responds to the host command and sends back 10 bytes of data, which are divided into four parts: command segment, data segment, checksum, and end flag.

2.3 Communication Tests The steps for the communication test are as follows.

1) Slave parameter setting. Slave number and unified communication rate are set for the electromagnetic flowmeter of each slave station.

2) Selected communication band. Each wireless data transmission station is provided with an 8-bit dial switch. By adjusting the dial switch, different frequency bands can be selected for the radio. All radio stations must select the same communication band, that is, the dial switch is set to be the same. Through experiments, non-interfering communication bands are selected for wireless communications.

3) Realize wireless communication. A communication command is issued by the PC of the master station. First, the address code is set to 1 in the message structure sent to the slave, and the function code is set to the number 00 corresponding to the instantaneous traffic. The start code and the end code are added together through the master station. The radio station sent out. After receiving the host command information, slave 1 generates 10 bytes of response information data, fills the requested data in the data segment, and sends it back to the master station. After receiving the master station, the function code in the message data sent to the slave is changed to the number 04 corresponding to the total traffic and sent again. After receiving from the No. 1 slave, the total flow value is filled in the position of the data segment and sent back to the master station again. At this point, the communication between the master station and the slave station No. 1 was completed, and the master station changed the address code to 2 to complete the communication with the slave No. 2 until the completion of the communication with the slave No. 50 was completed. process.

3 Selection and Installation of Digital Radio Antennas As production companies need to run many large-scale production equipment at the same time, the high-power and strong magnetic fields of these equipments affect the quality of wireless digital transmission to a certain extent, so the choice of wireless data transmission radio antennas has changed. It is crucial.

After installing and setting the correct hardware installation method, if it is still not possible to receive accurate and error-free information, check whether the installed antenna is appropriate. The position of the system master station is close to the large-scale production equipment operation workshop. If an ordinary sucker antenna is installed in the control room, the signal cannot be transmitted to the slave station. Therefore, the antenna must be set up in an outdoor, non-interference location to ensure transmission quality. This needs to extend the connection between the data transmission station and the workstation, and extend the data transmission station and the power supply to the outside. Since the length of the location from the outdoor installation point of the antenna to the indoor station is about 10 meters, the number of RS232 interfaces that the master station can use To transmit the radio station, if this distance is too far, the radio station needs to be replaced with an RS485 interface, and communication between the radio station and the workstation is accomplished through the RS485-232 conversion module. In order to obtain more stable and error-free communication data, the main station antenna uses a fiberglass antenna to replace the ordinary sucker antenna, which can reduce signal interference and ensure communication quality. In order to avoid damage to the equipment caused by strong currents during thunderstorms, lightning arresters must be added between the FRP antenna and the data radio.

The system's data transmission station is connected to an electromagnetic flowmeter. The selected electromagnetic flowmeter is an RS485 interface, and the station digital transmission station uses an RS485 interface. Slave stations are mostly installed in open locations outdoors, so using an ordinary sucker antenna can complete accurate data transmission. The sucker antenna needs to be installed on a ferrous object for better communication. Some of the data collection points of the secondary stations are located on the ground floor of large buildings, and the feeders are appropriately extended to ensure that the height of the antenna installation is not less than the height of the two-story building. If the data collection point from the station is placed under the ground, taking into account the underground signal absorption and the shielding of the manhole cover, the radio antenna of the station is placed on the surface of the manhole cover using a small rubber antenna or a custom corresponding antenna. At the same time, properly improving the power supply voltage and radio transmission power of digital radio stations can also improve the communication quality. The system is shown in Figure 2.

Figure 2 Connection of data radio and antenna

4 software design and function realization The software part mainly completes the scene signal acquisition, the processing and the computation, the result demonstration, the preservation and the printing and so on the function. The meter reading period is set to 6 minutes. The system initiates a data collection process every 6 minutes. Each time the data collection process is completed, the instantaneous water flow and cumulative water consumption of 50 water meters are collected in sequence.

4.1 Data Acquisition The control room workstation acquires the on-site signal through the communication between the host RS232 serial port and the wireless data transmission station, which is the core of the software part. VB language is an object-oriented programming language based on Windows operating system. VB has a MSComm control that manages serial communications. Using it requires only a few main parameters to set up a serial communication between the PC and the wireless communication module.

4.2 Database Design SQL Server is powerful and can fully implement all the functions of the database system. The system design database table is as follows: The database name is WXC; the data table is a water meter.

The workstation will display the field data collected from the serial port of the PC on the VB configuration screen and store it in the water meter form of the WXCS database of the SQL server database.

4.3 System Screen Creation The most important function in this system is real-time data display. The real-time data display screen is shown in Figure 3.

Figure 3 Real-time data display

Other functions include historical data query, data graph, report drawing, print operation, duty watch duty records, and other form interfaces.

5 conclusions The system adopts the wireless transmission management system to reduce the overall cost, that is, only one-time investment, no need to dig trenches, and the maintenance cost is low. The system has been commissioned to operate: It ensures the wireless transmission of water meter data in the plant area with a length of 2km and a width of 1km, and has stable operation, strong real-time performance, low BER, and meets all production requirements. The upper system is fully functional, capable of storing historical data for up to 1 year, providing a powerful guarantee for the cost analysis of production, reducing the amount of clean water and production costs, while reducing the labor intensity and improving the management level.