Application of communication technology in remote meter reading system

　　introduction

　　While the information society is gradually changing people's lifestyle and working habits, it also challenges some traditional ideas. With the progress of science and technology and the improvement of people's living standards, remote meter reading system has become an important part of "intelligent construction" in communities and universities. Remote meter reading system is produced to measure and manage the consumption of energy and resources such as water, electricity and gas, and provide basis for charging. At the same time, with the improvement of living standards, people's consumption of resources is increasing day by day, and the measurement, management and charging of resource consumption are becoming more and more complicated. Products that improve the management level and automation level are bound to emerge as the times require.

　　In order to solve the problems of traditional meter reading methods, such as cost loss, huge management cost, heavy workload of data statistics and calculation, difficult to guarantee the accuracy of billing, and great inconvenience to users caused by human statistical errors, the realization of automatic meter reading and automatic billing has become a necessary condition for the digital management of logistics in new intelligent communities or colleges and universities. The advent of remote intelligent meter reading system has completely changed the traditional time-consuming and laborious manual meter reading method. Without leaving home, the management department can accurately know the use of water, electricity and gas of users at all levels through the computer network automatic meter reading system. It can realize the functions of automatic meter reading, billing, statistics and remote on-off control. Through the networking with bank data, it can realize the functions of automatic transfer and charging, which reflects the high-tech and intelligent scientific management mode.

　　In foreign countries, the research on remote meter reading technology started earlier and more in-depth. From the formulation of standards to the production of special chip for meter reading, a variety of remote meter reading technologies have been relatively widely and successfully applied. In China, due to different national conditions, we can't copy it. We can only take our own development path on the basis of using foreign advanced technology. Although various remote meter reading technologies have been applied, they are not large in quantity and less successful. There is a large development space for the research of remote meter reading technology.

　　1、 Composition and structure of remote meter reading system

　　Remote meter reading is a kind of meter reading method, which is mainly through the measurement and data collection of remote intelligent terminal and transmitted to a specific system through network or other transmission methods, and completes other forms of operation in the system. It has the characteristics of accuracy, speed and real-time, and can complete the whole task of meter reading. Remote meter reading system is generally a network system composed of handheld terminal or central station computer, concentrator, acquisition terminal (or carrier meter) and meter. According to investigation and research, most remote meter reading systems are similar in structure, and have established a general structure as shown in Figure 1.

　　Note: the transmission medium is generally wireless transmission (such as GPRS / CDMA, GSM communication, etc.) or wired transmission (such as can, PSTN, RS485, optical fiber and TCP / IP communication, etc.).

　　1.1 meter

　　At present, electric meters in China are divided into mechanical meters and electronic meters. Because the electronic meter is higher than the mechanical meter in stability, accuracy, sensitivity, power consumption and anti-theft effect, the electronic meter is used in the centralized meter reading system. At present, most electronic meters on the market use advanced special chips for electric energy measurement, which are designed in combination with mature multi rate technology. They are designed and manufactured according to the actual power consumption of residents by using digital sampling processing technology and SMT process, and generally have a variety of functions. It can store electricity for many months; With calendar, timing and leap year automatic switching function, programmable rate and time period; Infrared communication or 485 communication, programming and meter reading can be carried out through handheld terminal or PC; Manual programming and manual meter reading can also be completed through the infrared remote control.

　　According to the data acquisition characteristics of the meter, the remote meter can be divided into three types: pulse output type, IC card type and word wheel recognition type:

　　(1) Pulse output meter. It is required that the meter must be powered on for a long time. Once the power is cut off, the meter will be unable to measure;

　　(2) IC card type. The measurement is similar to the measurement method of bus and telephone card. A certain fee is pre deposited on the card, which is purchased first and then used, so as to avoid the phenomenon of arrears.

　　(3) Word wheel recognition type. This kind of meter is similar to other mechanical meters (mechanical meters are relatively mature products at present, and the state also has relevant acceptance standards). It only adds an identifier on the basis of the original mechanical meters. There are no disadvantages of the above two meters. It is an ideal product with relatively mature remote meter reading at present.

　　1.2 collector

　　The acquisition terminal is designed for centralized meter loading in the meter box. It is used to collect the electric energy information of multiple user electric energy meters and transmit the data to the upper level of the system through the channel after processing. The development of intelligent collector is one of the core tasks of the development of remote meter reading system. The collector is mainly responsible for the management and measurement of the user's terminal meters. It is the core controller of the system. Its main functions generally include: communication node, energy consumption meter measurement, data storage, system parameter setting and storage, data conversion, self inspection and meter status inspection, remote on-off control, alarm management, etc.

　　In fact, the meter used in the general system to measure the energy consumption of electricity, water and gas is a new meter that can not only visually display the relevant energy consumption measurement data, but also generate the relevant energy consumption measurement pulse signal. In fact, it is an electricity meter, water meter and gas meter equipped with sensors. The sensor is essentially a pulse circuit unit based on magnetoelectric conversion technology and photoelectric conversion technology.

　　1.3 concentrator

　　Remote meter reading system is a network system with relatively many communication node modules. In order to improve the network speed and reliability of the system, the concentrator is the bridge of the meter reading system. It should not only complete the data communication with the front-end collector, but also complete the data transmission with the superior meter reading host. The main function of concentrator is to divide the whole meter reading network into several subnets, and each concentrator is a subnet. The concentrator is usually set in the unit of distribution transformer. Each distribution station area is a subsystem, and the concentrator is the main station end of this subsystem. The concentrator manages all equipment (acquisition module and acquisition terminal) on the low-voltage side through the low-voltage power line. The concentrator can complete data acquisition, storage, processing and reporting, receive the command frame of the master station and respond, such as parameter setting, clock calibration, etc., and local setting functions, such as setting system parameters, meter reading parameters, etc.

　　Concentrators are installed in residential buildings. The concentrator is connected with the computer in the control center through some communication mode (such as LAN, GPRS, can bus, GSM, optical fiber, etc.) and is responsible for managing the collector in the subnet. Under normal circumstances, each concentrator can manage up to 128 intelligent collectors, read and store the user's meter data according to the time interval set by the operation station. When idle, the system will patrol the status of each collector in turn.

　　1.4 handheld terminal and central station computer

　　In case of sudden communication failure, it is necessary to conduct local meter reading or manual on-site inspection due to abnormal power consumption, and set the parameters of the new meter for replacing the old meter, or use infrared handheld computer or portable computer from the acquisition terminal when the communication system is short of project funds and high operation cost, The data is read from the meter and then directly downloaded to the computer master station system.

　　Computer master station system is generally composed of server, printer and PC. It mainly receives the data transmitted from each concentrator and maintains and manages the data. To set various operating parameters of field equipment. It can also monitor the power consumption of each user in each station area, judge abnormal phenomena and prevent theft.

　　2、 Communication application technology of remote meter reading system

　　Remote automatic meter reading system is a system that does not require personnel to arrive at the scene, uses a specific communication mode to transmit all kinds of data recorded by the smart meter at the user to the computer network at the remote control end, and the software counts, analyzes and calculates the data. Automatic meter reading system is a new and advanced meter reading method, which integrates the most advanced computer and communication technology, and is updated with the continuous development of hardware and software of communication technology system. Therefore, it can be said that it is a developing technology. In principle, there is no relatively fixed way and concept, but in practical application, it is usually the comprehensive use of a variety of communication technologies to achieve the most ideal goal.

　　At present, there are many kinds of technologies used for remote meter reading in China, mainly including: automatic meter reading system for wired bus communication, automatic meter reading system for telephone line communication, automatic meter reading system for optical cable communication, automatic meter reading system for power line carrier communication, automatic meter reading system for wireless communication, automatic meter reading system for satellite communication, automatic meter reading system for cable TV communication, automatic meter reading system for cellular communication Infrared communication automatic meter reading system and other methods. When determining the communication mode, it is necessary to comprehensively consider the object faced by the system, the distribution of users, the number of users, geographical conditions, economic conditions, the expected goal, the expansion and upgrading of the system, and the compatibility with other networks. The following is a comparative study of several common communication methods.

　　2.1 RS485 bus

　　In wired bus communication, RS485 bus mode is common. RS485 bus is an international open fieldbus standard. Twisted pair differential transmission mode is adopted, which can be connected into two communication modes: half duplex and full duplex, and the farthest transmission distance is 1200 m. The differential input range is - 7 ~ + 12 v. The input sensitivity of the receiver is ± 200 mV, the input impedance is greater than or equal to 12 K Ω, and the number of standard connection points is 32, that is, the driver of each RS485 interface chip can drive 32 standard RS485 loads. According to the regulations, the input impedance of the standard RS485 interface is greater than or equal to 12 K Ω, and the number of corresponding standard drive nodes is 32. In order to adapt to the communication situation of more nodes, the input impedance of some chips is designed as 1 / 2 load (greater than or equal to 24 K Ω), 1 / 4 load (greater than or equal to 48 K Ω) or even 1 / 8 load (greater than or equal to 96 K Ω), and the number of corresponding nodes can be increased to 64128256.

　　RS485 bus communication mode has the following advantages and disadvantages in the communication process. The advantages are mature and simple technology; Under normal communication conditions, the communication is reliable and stable, and real-time communication can be realized; The disadvantages are that the wiring work is large, the communication channel is vulnerable to man-made damage and large-scale damage, it is difficult to eliminate the fault after damage, the recovery is slow, and the subsequent maintenance of the channel is large.

　　2.2 telephone line communication

　　Telephone line communication mainly depends on renting telephone network. It only needs to install modems on the host station transformer terminals respectively, but due to the long line connection time, it usually takes a few seconds to tens of seconds. Therefore, when the number of concentrators is large, the communication efficiency will be greatly reduced. Automatic meter reading technology based on telephone communication has been used for more than 20 years and is widely used. Its advantage is that the system avoids the shortcomings of high cost and large-scale capital construction of radio, optical fiber, cable and other systems; The disadvantage is that the line connection time is long. When the number of concentrators is large, the communication efficiency from concentrator to control center will be greatly reduced. In addition, if there are many leased telephone lines, the rental fee is also very high, so it is not suitable for high-capacity systems.

　　2.3 power line carrier communication

　　Power carrier communication is divided into high-voltage power carrier communication and low-voltage power carrier communication. Power line carrier communication is a special communication mode that uses the distribution line as the information transmission medium for voice or data transmission. It uses the existing distribution network as the information transmission carrier, so the cost is low. However, due to some time-varying characteristics of user power grid and the impact of sudden noise on data transmission, there is still a problem of "blind area" of meter reading. This problem has hindered the application of power line carrier technology in automatic centralized meter reading system. The advantages and disadvantages of high-voltage power line carrier communication are: the advantages are long transmission distance, simple system structure and good maintenance, so the application effect of high-frequency carrier is very good; The disadvantage is that the transmission of power carrier system on distribution line may encounter many difficulties, and the equipment is complex and difficult to promote. The advantages and disadvantages of low-voltage power line carrier communication are: as the bottom data channel of automatic meter reading system, it has the advantages of low cost, convenience and accuracy. The disadvantage is that the low-voltage distribution line carrier communication transmission performance is poor, which is mainly manifested in high noise, low impedance, large loss, large fluctuation, easy to be disturbed by the outside world, etc.

　　2.4 can bus

　　Controller area network (can) is one of the important field buses. It is a serial communication network developed by Bosch Company of Germany for automotive electrical control system, which effectively supports distributed control and real-time control. It is mainly used for various process detection and control.

　　It follows the OSI model and works in the data link layer and physical layer. Can bus is a fully digital, bidirectional and multi master fieldbus. It has attracted people's attention and is more and more widely used because of its high performance, high reliability and flexible design. At present, can has been gradually applied to other industrial control and has become an ISO l1898 international standard. Its advantage is that can can can be a peer-to-peer structure; Can can adopt non-destructive arbitration technology; Can can send and receive data in the way of point-to-point, point to multipoint and point to network. The communication distance is up to 10 km and the number of nodes can reach 110; The medium adopts cheap twisted pair, no special requirements, simple user interface and easy to form user system. The disadvantage is that multi-layer bus structure can not be adopted generally, which may lead to bus overload; It can not be interconnected with the Internet and can not realize remote information sharing; It is not easy to directly interface with the upper control computer; Communication distance is still limited.

　　2.5 optical fiber communication

　　Optical fiber communication automatic meter reading system adopts optical fiber transmission as the name suggests. Optical fiber communication technology has been greatly developed and widely used in recent years. Its advantages are large capacity, long relay distance, high transmission rate, free from the influence of lightning and switch operation, strong anti electromagnetic interference ability and so on. The disadvantage is that the investment cost is too high.

　　2.6 GSM communication

　　GSM (Global System for mobile communication) system is a relatively mature, perfect and most widely used system in the mobile communication system based on time division multiple access technology. GSM remote meter reading is to realize the remote transmission of intelligent meter data by using the functions provided by the telecommunications department, that is, it is a new idea to realize automatic meter reading by using GSM network short message service. The system is mainly composed of three parts: meter reading master station, GSM network and GSM meter reading terminal equipment. Firstly, the meter reading master station composed of PC and communication module is connected to GSM network, and then uses short message service to send commands to meter reading terminal equipment according to a certain protocol format. Its advantage is that it occupies less system resources, fast network construction speed and less investment cost. The disadvantage is that GSM SMS can only be transmitted in one direction, and the number of characters per time cannot be more than 160 or 70 Chinese characters.

　　2.7 GPRS communication

　　The GPRS based wireless switching system is a wide area wireless switching system. GPRS sends and receives data in packet switching mode through China mobile GPRS service gateway GGSN, and uses the existing wireless communication network to realize remote meter reading. The technology is mature and reliable, but the network front-end communication module and operation cost are high, so this technology is rarely used at present. However, with the continuous reduction of China Mobile tariff, GPRS will certainly provide an efficient and low-cost wireless data transmission method.

　　Its advantage is that it has a wide access range and is not limited by region and location; High transmission rate, support transmission at different rates, and meet the application requirements of remote meter reading; Provide real-time online service, which can provide fast and real-time connection and ensure the real-time communication; Billing by traffic is especially suitable for remote meter reading, which is an intermittent, frequent and small (occasionally large) data transmission mode; It supports TCP / IP protocol and X.25 protocol, and can communicate with the Internet, breaking through the limitation of data flow in GSM communication.

　　The disadvantage is that GPRS is charged by traffic at present, and the operation cost for large amount of data is high; The real-time performance is poor, especially in holidays. The load of the system will reach the peak. The system and network are blocked seriously, the information is not smooth, and the useful information cannot be sent or received in time, thus delaying major events; The system security is poor. Because GPRS sends data through the Internet, but the current network security is not high, it is more and more vulnerable to attack and paralysis; The quality of service is subject to the service of the operator, which may be the problem of GPRS system or network, which is prone to "wrangling".

　　2.8 TCP / IP network communication

　　There is no doubt that TCP / IP (usually it refers to the international protocol of transmission control protocol) is the most successful communication protocol so far. Its success is proved by its application on the Internet, the largest open network system built today. TCP / IP is an open communication protocol. Based on this feature, the data collected by the collector can be transmitted between the upper computer management center computer and the lower computer high-performance chip.

　　TCP / IP is not a physical thing that exists at a certain time and place. It is a set of protocols that enable users of any computer, modem and Internet service provider to access and share information on the Internet. Because of the popularity of TCP / IP, the host computer management system can not only communicate with the concentrator, but also be accessed by the Department at any time. TCP and IP are two independent and closely integrated protocols. TCP is responsible for the connection with the remote host, while IP is responsible for addressing, so that the message is sent to its place. When the lower computer wants to transmit the electric energy data message to the upper computer, it is responsible for connecting the lower computer and the upper computer host, and looking for the address of the upper computer in the network, so that the message can be sent to the upper computer smoothly. Its advantages are platform independence, good damage recovery mechanism, efficient error rate processing, being able to join the network without interrupting existing services, low data overhead and so on. The disadvantage is that in general, the cost will be slightly higher than that of RS485 controller, and it is difficult to ensure the requirements of real-time data and poor data security and reliability.

　　3、 Conclusion

　　To sum up, the remote meter reading system integrates computer technology, communication technology, power consumption and measurement technology. It uses remote transmission technology and today's developed computer technology and network technology to connect each billing terminal and management center, and automatically read the user's consumption data regularly or in real time. Especially in the process of data transmission, choosing what kind of communication mode is suitable or the combination of several communication modes is not only a hot issue in the current research, but also one of the core tasks of the remote meter reading system. Through the above analysis and comparison, according to its advantages and disadvantages, when determining the communication mode, it is necessary to comprehensively consider the object faced by the system, the distribution of users, the number of users, geographical conditions, economic conditions, expected objectives, the expansion and upgrading of the system, and the compatibility with other networks, It is of great and far-reaching significance for the implementation of intelligent community and digital logistics management project in Colleges and universities.