Principles and application status of flow meter selection in urban water industry

This article outlines:
 
The tap water industry is an industry that is closely related to the daily lives of ordinary people and is also closely linked to the production of many companies. Urban water supply systems are all implemented through different pipelines. For tap water flow meter measurement, a set of flow meters that can adapt to different pipelines and different measurement environments is required. At present, the domestic water supply industry mainly uses electromagnetic flowmeters, ultrasonic flowmeters, turbines, vortexes, orifice plates, Venturi, etc. for large-caliber water supply and drainage sites. There are also Pitot tube differential pressure flowmeters and mechanical water meters such as horizontal propeller water meters, vertical propeller water meters, and compound water meters.
 
With the increasing maturity of electromagnetic flowmeter and ultrasonic flowmeter technology in recent years, their application has become more and more common and has developed the fastest. Among them, the external clamp ultrasonic flowmeter is deeply loved and welcomed by users for its convenience of installation without breaking the pipe, and has been widely used throughout the country. Runzhong Instrument Technology Co., Ltd. is a company specializing in the production of electromagnetic flowmeters and clamp-on ultrasonic flowmeters. It has rich experience in production, selection and installation. This article is written to share with you some experience in the selection, use and calibration of metering instruments for pump rooms, trade settlements, and regional metering. I hope to provide some help to friends in related work.
 


1. Selection principles for large-caliber water supply flow
　　To use the flow meter well, selection is the key. At present, there are more than 100 manufacturers of large-caliber flow meters and more than 50 models. According to your flow range, installation environment, economic conditions, management level, and the cost-effectiveness of different flow meters at home and abroad, determine the ideal model.
　　1. Water metering instrument for water inlet and outlet of water plant pump room
　　The accuracy and reliability of the flow meter installed in the water plant's inlet and outlet water pipes is related to the economic accounting of the water plant, the reasonable calculation of the difference between production and sales (leakage rate), and it is also the most important basis for the production and operation of water supply enterprises. Since the water plant pump room can guarantee power supply and has good installation conditions, the first choice should be the electromagnetic flow meter with a standard pipe, followed by the sonic penetrating ultrasonic flow meter. Because the electromagnetic flowmeter has high measurement accuracy (±0.3-0.5%), the straight pipe section requires a relatively short length, the measured inner diameter will not change due to long-term use, and the maintenance is relatively simple.
　　2. Trade settlement and charging flowmeters
　　In the past, the trade settlement flowmeters we usually used were mechanical water meters. With the development of technology, more and more electronic water meters (flowmeters) are used as replacement products for large-diameter billing water meters. Electromagnetic flowmeters, ultrasonic flowmeters, vortex electromagnetic flowmeters, etc. (Note: The new water meter calibration regulations have included this type of electronic water meter), especially electromagnetic flowmeters and ultrasonic flowmeters with standard tubes. The biggest features of these flowmeters are:
　　(1) High measurement accuracy, usually ±1%-±0.3%, among which the electromagnetic flowmeter with standard tube has the highest measurement accuracy and the most linear.
　　(2) According to actual conditions, a flowmeter without AC power supply can be selected, and the lithium battery power supply time can be up to 6 years.
　　(3) The measurement range is wide (up to 1000:1), that is, its maximum flow value is larger than the overload flow value of the mechanical meter, and the starting flow value is smaller than the mechanical meter.
　　(4) It is basically maintenance-free. Especially protected from lightning strikes.
　　(5) It has accurate cumulative and instantaneous output and communication interface, which facilitates data transmission, which is also unmatched by mechanical meters.
　　3. Regional metering flow meter
　　With the development of science and technology, the in-depth scientific management of tap water enterprises, the necessity and importance of regional metering have gradually emerged. Regional metering has three main functions:
　　(1) Rationally dispatching urban pipeline flow to meet user water demand, while saving energy for enterprises and reducing production costs. The installation of urban main pipeline flow meters provides a basis for controlling the flow of water plant pump units and the reasonable dispatching plan of the flow direction and flow of urban water supply pipelines;
　　(2) Conducting responsibility and economic assessment of internal supply and marketing of enterprises;
　　(3) Decomposing the leakage rate of enterprises. Scientifically analyze some areas with high leakage rates to find out the reasons, such as water leakage, water theft, or inaccurate metering, and take corresponding measures in time to reduce the leakage rate.
　　In order to accurately and reliably monitor and calculate regional water consumption and to deeply understand and study the changes in leakage rate, in recent years, many water companies have increased the online measurement data analysis of regional pipeline flow, flow direction, pressure, water quality detection, etc. Practice has proved that regional metering has brought good social and economic benefits to water companies. The smaller the regional metering range, the better. However, choosing a good flow meter is also the key. The type of flow meter to be used should be determined according to different requirements, different environments, different economic conditions, and different management levels.
　　For the metering instruments used for main pipeline water volume detection and dispatching, these flow meters generally have large calibers and low measurement accuracy. On the other hand, considering not affecting large-area water supply, it is recommended to use electromagnetic flow meters with standard tubes for new installations, and insert ultrasonic flow meters or insert electromagnetic flow meters with relatively small investment and easy installation can be considered for old pipelines; for production and sales differential zone assessment, flow meters that monitor leakage rate changes are best to use standard tube electromagnetic flow meters and ultrasonic flow meters with high measurement accuracy. If the power supply of these instruments is difficult to guarantee and difficult to install, it is recommended to use flow meters that are technologically advanced and have superior performance and are free of mains power. The standard tube lithium battery electromagnetic flowmeter currently provides a maximum DN600mm (the current market price of lithium battery electromagnetic flowmeters is 1-2 times more expensive than electromagnetic flowmeters powered by mains power), and ultrasonic flowmeters are DN400mm. Of course, ancillary equipment such as remote transmission systems and pressure instruments must also use devices that are free of mains power.
　　For flow meters powered by mains electricity, it is recommended that manufacturers provide 24V DC power supply, equipped with a good 24V charger, storage battery, power outage timer, and take appropriate lightning protection and anti-interference measures, which is conducive to the reliable operation of the flow meter.
　
2. How to scientifically manage flow meters
　　Scientific management of flow meters includes remote monitoring, data management, instrument verification (calibration), repair and maintenance. With the rapid development of electronic technology, remote detection has developed from the original single radio station to the current GPRS, CDMA, GSM, ADSL, PSTN (telephone network) and other data remote transmission. Let's talk about my experience. The
　　data remote transmission of large-caliber flow meters is divided into two categories: online remote transmission and intermittent remote transmission. Some flow meters such as water plants, regional metering, large water users, urban and rural junctions, etc., these meters need to be always online for detection, and it is more appropriate to consider GPRS, CDMA, PSTN and radio stations in the selection; considering the installation workload, investment cost and operational reliability, GPRS and CDMA mobile communication networks are preferred. For small data remote transmission, it is only necessary to monitor the water use situation every day, so it is more appropriate to choose GSM. Currently, there is a GSM remote transmission device that uses lithium batteries to power about three years (the battery price is less than 100 yuan), has a waterproof grade of IP68, and is as big as a telephone. Activate it once a day, and you can package and transmit the six parameters of 24-hour cumulative flow, instantaneous flow, power supply conditions, access control, etc. to your computer through GSM for analysis, storage, and printing. The price and operating cost of this device are relatively low, and it can also be used as a portable mobile data remote transmission instrument. It can also be regarded as the result of the development of modern science and technology. Therefore, the use of this remote transmission device for trade settlement flow meters and large-caliber water meters can fully meet the needs of data transmission.
　　The data management of the instrument can be configured with different remote transmission devices for online remote transmission and intermittent remote transmission as needed. If necessary, the data can be loaded into the information center database for permanent storage, printing, and transmission to department leaders and decision makers of the head office.
　　
3. Verification requirements for flow meters:
　　Verification (calibration) of flowmeters: At present, the country has no online (calibration) verification procedures. It is recommended that the Water Supply and Drainage Association issue a method for online calibration of flowmeters as soon as possible for trial use for 1-2 years, and then improve it according to the actual situation and report it to the Ministry of Construction as a ministerial standard. If there is no abnormality in the flowmeter or the inspection during use meets the requirements, the online calibration cycle is generally two years. For flowmeters above DN400mm, it is recommended to calibrate once a year, especially for flowmeters using non-standard pipes. Pay special attention to the phenomenon that the inner diameter of the pipe becomes smaller, causing the flowmeter to be faster, which cannot be detected by portable ultrasonic comparison (unless there is a standard pipe section before or after the flowmeter). For flowmeters that are disassembled and sent to the calibration station for compulsory inspection, considering the country's implementation regulations and comprehensive management costs for compulsory inspection of measuring instruments over the years, it is recommended to extend the period to 4 years for standard pipe sensors and large-diameter flow meters (such as electromagnetic and ultrasonic water meters) whose linings have taken anti-corrosion measures.
　　It is also worth mentioning that some authoritative metrology departments not only want to ensure the accuracy of instrument measurement, but also pay attention to the high income of calibration (verification) fees. They are preparing to establish flow calibration standards, and shorten the cycle of disassembly and inspection, which increases the workload and economic burden of enterprises, resulting in unrealistic and disharmonious phenomena.
　　
IV. Conclusion of this article
　　Today, the world's science and technology are developing rapidly, and various new processes, new materials and new technologies are constantly being introduced. The same is true in the instrumentation industry. For managers and technical workers, they need to keep pace with the times, constantly update new knowledge, new thinking, broaden their horizons, pay attention to the development direction of the international industry, summarize experience, learn from each other, and dare to innovate, so that the flow meters of this unit can be made better and better.