Technical status of meter automatic meter reading system

one. Technical status

The GB/T 778.1- 3-2007 standard divides the water meter into three categories: "mechanical water meter", "water meter with electronic device" and "electronic water meter" in terms of technology and structure. Water meter with electronic device is based on speed or volumetric mechanical water meter, adding electronic components, so that it has the functions of sensory acquisition, operation processing and data exchange of flow measurement parameters (such as impeller rotation speed) to meet the demand of water consumption. Automatic reading and water fee collection management and other needs.

Meter automatic meter reading system consists of software and hardware. The hardware components mainly include: water meters with electronic devices, network facilities, data collection and copying devices, and terminal equipment. The software includes: embedded data processing software, network management software, data transmission and charge management software.

1. The main technology used

After more than ten years of development, improvement and improvement, China's water meter automatic meter reading system products have initially formed a relatively complete product technology system. In particular, significant progress has been made in sensor acquisition of flow measurement signals, safe and efficient data transmission, and reliability, longevity, and cost-effectiveness of products. The main technologies and features currently used:

(1) Signal Sensing and Acquisition Technology The sub-system pulse sensor acquisition method sends a signal through a water meter impeller or a counting pointer to output a pulse signal that is proportional to the water flow rate; each meter needs to have its own dedicated external line and an outdoor collector. Calculate the actual water consumption after the pulse accumulation; The large amount of projected wiring, pulse susceptible to internal and external interference; Line failure or power failure can interrupt the signal, the data recovery difficult; The use of low reliability, high installation and maintenance costs; Mechanical readings and remote data are difficult to completely match.

Bus-based pulse sensor acquisition method sends water through the meter impeller or counting pointer, and outputs a pulse signal proportional to the water flow; a computer chip and a battery are provided in the table (bus power supply mode is also available), and the number of pulses is accumulated and stored internally. Water consumption; The effect of vibration, impact, etc. of the water and fluid during measurement easily leads to inaccurate output pulse counting; it is difficult to completely match the mechanical reading of the water meter with the remote data.

Bus-based read-ready acquisition method Word wheel coding method: Through the absolute coding of the position of the mechanical counter word wheel, the word wheel reading is completely consistent with the coded output signal; the computer chip is provided in the table, but no built-in power supply is required; the outdoor collector When the signal is collected, it supplies power to the water meter and reads out the water (coding) data. The reliability is high, the cost is low, and the electromagnetic compatibility is strong; the encoder requires a relatively high production process.

Image sensing method: Take off the mechanical character wheel reading through the off-board image sensor, and use the bus to transmit the image signal to the outdoor collector; there is no power supply in the water meter, and the power is supplied to the sensor to acquire the reading image during signal acquisition; the sensor is easy to install; image data And large storage capacity, high requirements for transmission and system; image conversion and recognition software is complex. (2) Data transmission and network technologies Wired data transmission and networking methods Several grades of wired ad hoc networks consisting of RS485 or M-BUS buses are intranets, public telephone networks (PSTN) or wireless public networks (such as: GSM, GPRS, CDMA, etc.), as well as the wired network data transmission system composed of hand readers. Wired network is the main area within the area, and the public network is used as the information transmission channel outside the area. The technology is relatively mature; the amount of wiring within the area is large, and installation and maintenance costs are high. The application of power lines as signal transmission carriers is also underway.

Wireless data transmission and networking form a data transmission system based on short-range and low-power wireless communication technologies. Some areas within the area are referenced to wireless sensor network (WSN) technologies for networking. Outside the area, public networks are still used as information transmission channels. The area does not need wiring, installation and maintenance is convenient, the cost of networking is low; the data is susceptible to electromagnetic interference, the power supply is required in the table, and the network standards are not uniform; commercial applications need to be further matured in technology.

(3) Network data management technology Data transmission and communication protocol The data transmission protocol currently implements the "Technical Specifications for Data Transmission of Household Meters" (CJ/T 188-2004). "Transmission technical conditions" stipulate the physical layer and data link layer protocol in the centralized meter reading system for household instruments (including water meters, etc.), the physical interface between the master and slave stations and their characteristics, and the composition of information exchange frames. Traffic and error control have been specified.

Before the data transmission security management data is sent, the data is required to be encrypted, and the data is decrypted after being received. Electronic key (ECB) method is used to encrypt the data and send data. The encryption algorithm uses the standard cryptographic algorithm of 64-bit packet of secret key.

(4) Power supply technology The power supply method in the table is mainly powered by a high-energy lithium battery. Energized control valve water meter is a reliable valve, generally used two lithium battery points "strong" and "weak" loop power supply; there is also the use of ultracapacitors usually charge, off the valve when the discharge and other methods.

The external power supply mode is powered by an external concentrator or collector through the bus to the water meter. Concentrators or collectors generally use large-capacity batteries or convert them to direct current after receiving AC power.

2. The main problem

The performance of a water meter with an electronic device is a key factor that restricts the metering characteristics and reliability of the water meter automatic meter reading system. Breakthroughs in this area need to be improved and innovated in mechanical water meters and sensing technologies.

Short-range wireless communication technology is also a technical difficulty at present. Its emergence can not only solve the inconvenience and diseconomy of wired network wiring, but also brings problems such as unreliable signal transmission and battery life.

The power supply problem is one of the biggest bottlenecks with electronic device water meters. It affects the popularization and application of automatic water meter reading systems, and it also brings many difficulties to product design.

two. development trend

After years of practice, the understanding of the development trend of water meter automatic meter reading system inside and outside the industry is gradually unified. Although there are still some differences and disagreements, but the overall technology trends are still relatively consistent, that is: the development of the sub-system to the bus system, the pulse acquisition method to the word wheel data directly read the development of the way, wired data transmission gradually The development of wireless data transmission, as well as the micro-power consumption of the watch and data transmission, the improvement of the performance and reliability of the base table, and so on. The focus of technological development is mainly reflected in the following aspects:

(1) Sensing technology converts word wheel readings into digital coded output by measuring the position of the counter wheel. Accurate coding methods and algorithms, reliable absolute encoders, and standardized production and assembly processes are prerequisites for ensuring effective and reliable signal sensing and acquisition.

Common coding methods are: binary code, Gray code, single-channel short code, etc. (At present, there are many kinds of coding technologies in the country that are granted patents); encoding signal sensing methods include: direct-type or reflective photoelectric sensing methods, and electricity. Eddy current sensing method, contact potential sensing method, etc.; Power supply method: no battery in the base meter, and the bus is instantaneously powered when the signal is collected.

Obtaining character-encoded data through image sensing is also a promising sensor technology.

(2) Transmission and networking technologies Wired networking: M-BUS and RS485 bus technologies and data communication protocols are used to ensure the reliability and security of data transmission. The addition and decryption of data and the use of anti-jamming technology are key to wired networking technology.

Wireless networking mode: based on existing short-range, low-power, non-standard ad hoc network technology, there are standard communication protocols, powerful network functions, good anti-interference and compatibility, low power consumption and low networking costs. The direction of development. The short-range, low-rate, and micro-power wireless sensor network technologies worthy of attention include: Zigbee, Ultra Low-Power Bluetooth (ULP), and Z-Wave. They have the basic features that water meter automatic meter reading systems expect, such as ultra low power data reading and transmission, ultra-low cost, wireless communication standardization and network topology management, high security and reliability, short distance and high capacity. Communication, license-free frequency bands, direct-sequence spread spectrum (DSSS), improved signal-to-noise ratio, and more.

(3) Micro-power design and power supply technology Most electronic meters with electronic devices (such as: bus pulse acquisition water meter, wireless networking water meter, card water meter, heat meter, etc.) need to bring their own battery-powered work, in order to ensure that the water meter Reliable work The battery is often designed to be non-replaceable. The use of micro-power circuit design and power saving algorithms is an effective way to extend battery life.

The development and industrialization of high-capacity batteries (such as new types of lithium batteries, fuel cells, etc.) will surely provide longer-life, smaller-sized power supplies for water meters with electronic devices; use of light energy, hydropower, radio energy, etc. Electricity storage and power supply technologies are also important research areas for future solutions to the power supply of automatic water meter reading systems.

(4) Water meter technology The main function of the water meter is to measure the water flow correctly and reliably. Therefore, improving the technical indicators of the water meter's base meter is an important guarantee for the meter's automatic meter reading system to work effectively. Should be in: flow measurement range, small flow measurement characteristics, measurement accuracy, use reliability and life expectancy and other aspects of a comprehensive upgrade. Medium and small caliber electronic water meters (such as: electromagnetic water meter, jet water meter, ultrasonic water meter, vortex street water meter, etc.) Because there are no moving parts in the measuring tube, the pressure loss is small, the measurement range is wide, and the accuracy is high, the next step is to automatically copy the water meter. The base table of the table system has a good development prospect.

Three . Conclusion

The water meter automatic meter reading system is an emerging technology that has been developed over the past decade or so. Although many efforts have been made in various technical fields and technical levels, a great deal of beneficial practical activities have been carried out in residential districts around the country, summing up many valuable experiences. experiences and lessons. However, as a whole, the technology is still in the stage of development and improvement, and it needs further innovation and improvement.

With the development and maturity of water metering technology, sensing technology, wireless communication technology, network transmission technology, and power supply technology, as well as the expansion of water resources management and the speeding up of intelligent community projects, it is used as a water measuring instrument and data transmission. The water meter automatic meter reading system of management tools must have a very broad application prospect and good development space.