Principle and application of remote meter reading monitoring system

　　Automatic meter reading (AMR) system refers to a system that uses sensing technology, automatic control technology and computer network technology to automatically read and process the water, electricity and gas meter data of urban residents, and comprehensively process the information. Automatic meter reading technology is accurate and convenient, which can not only improve the work efficiency of the management department, but also meet the needs of modern users for water, electricity and gas payment.

　　With the rapid development of electronic technology, especially communication technology, people begin to use new ideas and new methods to solve the problem of automatic meter reading. The main ways are special line mode, public channel mode, wireless mode and so on. It has clear provisions on the definition, function and technical indicators of residential remote meter reading system. The remote meter reading system has greatly promoted the standardization of residential remote meter reading system products.

　　1. Current table end data acquisition method

　　People know that to convert a mechanical meter into a digital meter, the angle of mechanical rotation (angular displacement) must be converted into a countable signal.

　　The original conversion was to use mechanical contact switches to form pulses. In the 1980s, photoelectric technology was gradually popularized,

　　It has been widely used. In the primary stage of meter reading system, photodiodes and photosensitive triodes are mostly used, including visible light and infrared light. Their application modes are penetrating and reflective.

　　Photoelectric direct reading is one of the modes of reading meter end data in recent years. Its basic principle is to encode the word wheel according to the angle and read out the number of the position of the word wheel through photoelectric. The biggest advantage of photoelectric direct reading is that it does not have to supply power for a long time. It can only supply power when reading data. However, its structure is complex and easy to be polluted by water, oil and gas, resulting in inaccurate meter reading data. The most important problem at the meter end is to solve the problem that the signal increment must maintain a one-to-one correspondence with the mechanical rotation, which is very reliable.

　　It is precisely because each manufacturer of automatic meter reading system has different solutions to the meter end, and the response effect in the market is naturally different.

　　2. Problems caused by signal transmission

　　There are many ways of signal transmission in remote meter reading system, wired and wireless. In each mode, its topology and communication protocol directly affect its communication quality.

　　According to the current technological development level, the vast majority of remote meter reading systems adopt wired mode, or some wired mode. The initial construction investment of wired mode is large and the project is difficult, but the communication quality is good. However, due to the increase of high-rise buildings and high-end houses in recent years, the wiring work is facing new problems. In addition to the engineering difficulties, it is difficult to solve the user satisfaction, especially for the existing users, it is difficult to achieve household satisfaction if they want to drill holes in the indoor wall. Wiring in the residential area will also affect the cultural landscape of the residential area. In general, the property management and owners of the residential area are not allowed to break the ground or set up wires in the air.

　　Wireless transmission communication has developed rapidly in recent years, especially after the opening of 433MHz frequency band, many manufacturers have introduced this technical advantage into the automatic meter reading system, and some enterprises have even directly introduced the finished module integrated with data acquisition and transmission in western developed countries, but it involves many problems such as signal link and networking, which is not ideal, Promotion is difficult to continue.

　　GPRS technology is a hot spot in the current automatic meter reading system. Its advantage is that it borrows the ready-made communication platform of China mobile communication and does not need users to maintain and manage themselves. However, there are many manufacturers of GPRS communication equipment. Although some systems choose GPRS, they do not choose a GPRS with excellent performance, or the GPRS parameter setting does not reach the best state, which makes the data transmission quality and efficiency low, and directly affects the working efficiency of the automatic meter reading system.

　　3. Further optimize the system platform

　　The central control software and working platform are the core of the automatic meter reading system. It determines whether the system platform is efficient, reliable and freely applied.

　　Over the past ten years, the automatic meter reading system has made great progress through the promotion of scientific research institutions and enterprises and the efforts of engineers and technicians. The new automatic meter reading system scheme has been mature and has been gradually popularized and applied in the market.

　　The second chapter is the overall design outline of gas remote meter reading system

　　1、 General criteria for the design of gas remote meter reading system

　　When designing products, we must focus on the following aspects.

　　Safety: most of the gas meters are installed indoors. Due to the manufacturing reasons of the base meter (membrane gas meter) or the mistakes in pipeline installation, the gas leakage can not be underestimated. It is required that the remote meter collector in the meter reading system must eliminate the possibility of causing sparks and ensure the personal and property safety of residents.

　　Accuracy: in the process of data acquisition and data transmission, the reliability of data must be guaranteed. In case of power failure, the data cannot be lost.

　　Reliability: from the data collector to the monitoring center, it involves multiple links and facilities. Each operation equipment and storage equipment must be safe and reliable.

　　One time meter reading success rate: meter reading success rate is an important symbol to measure the reliability and efficiency of meter reading system.

　　Environmental adaptability: environmental adaptability includes the climatic environment and anti-interference environment in which the system works. It must work reliably under the temperature difference of 60 ℃ in winter and summer and 90% humidity. It can work safely and reliably under the conditions of power interference, external RF interference and electrostatic interference.

　　System self inspection function: the meter reading system involves a wide range, large quantity and dispersion. The system must have automatic diagnosis function and disconnection alarm function to facilitate the repair of the system.

　　2、 Working principle of the system

　　The remote meter reading monitoring system uses the remote transmission gas meter to realize the collection and measurement of gas consumption.

　　When collecting data, the collector collects the gas data through the header collector in the remote meter through RS485 / MBus bus, processes and stores it, and then the collector uploads the data to the concentrator through the wireless data transmission module. The main function of the concentrator is to collect the data uploaded by each collector and upload it to the monitoring center of the meter reading system through GPRS / CDMA after processing. When meter reading is required, the computer of the monitoring center sends the acquisition command. After receiving the command, the collector forwards the acquisition command to all collectors. After receiving the acquisition command, the header acquisition board judges whether it is the command sent to the terminal, If yes, the data stored on the header acquisition board will be transmitted back to the monitoring center, so as to realize remote meter reading. At the same time, the monitoring center analyzes the returned data. If it is abnormal alarm information such as disconnection alarm, it will send an alarm signal. If it is meter reading data, it will store the data in the database. Through the analysis and comparison of historical data, it will judge whether the suspicious user such as abnormal gas is available. If so, it will send an alarm message, So as to complete the collection and monitoring of user table data by the monitoring center.

　　3、 System composition, structure and main functions

　　1. System composition

　　The overall structure of the gas remote meter reading monitoring system is mainly divided into three layers:

　　The first layer: the data acquisition subsystem to realize the data acquisition of gas meter;

　　The second layer: the communication subsystem mainly realizes the function of remote data communication;

　　The third layer: the monitoring and management center that monitors and manages the gas data and equipment at each layer.

　　2. Remote transmission gas meter

　　The mechanical gas meter is refitted and equipped with gas meter collector.

　　3. Collector

　　Each collector can collect and store the data information of gas meter through RS-485 / MBus bus. At the same time, detect whether the gas meter is abnormal, and receive and forward commands.

　　4. Concentrator

　　Collect and store subordinate collector data in real time and regularly; Listen to the communication request signal of the communication subsystem, and carry out data transmission and forwarding commands with the communication subsystem.

　　5. Monitoring and management center software

　　Complete and issue meter reading and control commands; Complete real-time and regular gas meter reading tasks, store and manage gas data; Realize the functions of automatic charging, printing reports, chart analysis and so on; Monitor the status of each layer and deal with abnormal events.

　　Chapter III principle and application of main equipment of the system

　　1、 Concentrator

　　The concentrator is mainly composed of GPRS communication unit, monitoring thread unit, data transmission module unit and main control program. Its main functions include two aspects: one is to issue meter reading monitoring instructions (meter reading, monitoring, timing, etc.), and the other is to collect the data and status information of each collector.

　　Working principle of concentrator

　　In the remote meter reading system, the hardware topology is tree structure. The monitoring center is the root of the system, followed by concentrator, collector and remote gas meter, which is the end of the tree system. The monitoring center supports 1018 concentrators, 60 collectors for each concentrator and 256 remote meters for each collector.

　　The function of the concentrator is to receive commands from the monitoring center, including data acquisition, meter calibration, time calibration, valve opening, valve closing, etc. After receiving the command, the concentrator will send the command to the collector after recognition, and reach their own remote transmission table through the collector. After execution, the collector will summarize the situation of each table and return it to the concentrator, and the concentrator will return the collected information to the monitoring center.

　　As the concentrator is far away from the monitoring center, it is also hundreds of meters away from the collector. In the specific project, GPRS / CDMA public communication platform is adopted for the communication between the concentrator and the monitoring center. Between the concentrator and multiple collectors, the principle and method of wireless communication point-to-multipoint are adopted, and the open wireless frequency band data transmission module is adopted.

　　The concentrator will automatically send meter reading commands to each collector every certain time, and pre store the returned data into the SDRAM memory of the concentrator. When the concentrator receives the meter reading command from the monitoring center, it will directly take out the data from the SDRAM and send it to the monitoring center, which can greatly shorten the meter reading time and meter reading success rate.

　　2、 Collector

　　The function of the collector is similar to that of the concentrator. Its upper end is the concentrator and its lower end is connected with RS485 / MBus bus. 256 remote meters can be connected on the bus. For the lower end, it can be regarded as a hub. Different from the concentrator, the upper end of the collector is the data transmission interface, and the other party of communication is the concentrator; The lower end of the collector is a wired interface, which communicates with multiple remote meters according to RS485 / MBus interface and protocol.

　　The collector sends commands to each remote meter one by one in the form of polling within the specified time. The remote meter receives the commands belonging to this meter and executes meter reading data reporting or other control commands according to the command attributes. The collector receives the data returned from the remote transmission table and saves them all in the order of table number. When the collector receives the concentrator command, it will return the latest data of the polling result to the concentrator. At the same time, the collector is responsible for receiving the command from the monitoring center forwarded by the concentrator in real time and sending it to the execution unit of the gas header collector in time. In case of abnormal conditions such as disconnection, it will be sent to the concentrator in time and forwarded by the concentrator to the monitoring center, so as to realize the real-time monitoring of the user table by the monitoring center.

　　3、 Gas meter collector

　　The gas meter header collector is a key component of the remote gas meter. The problem that the remote meter reading system must solve is to ensure the accuracy of the front-end meter header data.

　　There is a sensing device in the gas meter collector. Its basic principle is to make the magnetic sensor produce switching action under the action of magnetic field array, so as to convert the mechanical rotation into pulse signal.

　　Microprocessor is the core device of the meter board, which controls other parts.

　　RS485 / MBus bus interface is the gateway between the meter board and the system bus. It is the only way in and out of the data. Once it is damaged, the meter board cannot communicate with the collector.

　　As an executive unit, the motor valve drive interface completes the function of opening or closing the valve under the instruction of the microprocessor.

　　The counting pulse conversion interface recognizes the pulse signal sent by the sensor and completes the incremental counting. In case of mains power failure, it is powered by the self-contained battery of the system to maintain the accuracy of counting.

　　The alarm identification interface includes disconnection alarm and antimagnetic alarm. Once the microprocessor determines that the alarm is generated, it shall take countermeasures to alarm the system, close the valve, and refresh the bad records of the user's personal file.

　　4、 Composition of meter reading monitoring center

　　The hardware part of the monitoring center includes computer, server, GPRS and network interface. They are not different from common equipment. Refer to: configuration of remote meter reading system.

　　The monitoring center software mainly includes three parts: meter reading server software, monitoring software and client application management software. Its functions have been listed in the monitoring management center software and will not be repeated.