Technology and application of flow meter in the ho

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Water supply industry flow meter technology and application

water supply industry application flow meters are divided into two categories: incoming raw water, outgoing finished water, water supply to users and other handover settlement measurement, and the flow and measurement/control of the internal process flow of the water plant

before the 1950s, traditional venturi differential pressure flowmeter and end-user toll mechanical impeller water meter were used for water production and water supply handover and settlement instruments. In the 1960s abroad and the mid 1970s in China, large-diameter electromagnetic flowmeter appeared, which began to break the monopoly of Venturi instruments on large-diameter water flow instruments. In the mid-1970s, there were other large pipe runoff meters with measurement principles, such as plug-in turbine flowmeter, averaging tube flowmeter, ultrasonic flowmeter, etc. These instruments have their own characteristics and are suitable for different applications

installation of flow instruments in water supply industry

before the 1970s/1980s, the water supply industry in China was more stable in public utilities. Water plants, pipes, sales and distribution belonged to the same enterprise. The application of flow instruments was limited to the internal process control of water plants (such as the flow control of raw water/coagulant ratio in the water purification process) and the water consumption charge measurement of end users. Only a few water plants were equipped with factory produced water metering instruments. In order to improve efficiency and control pipe leakage, the water supply industry implements the separation of production and marketing, that is, between the two independent enterprises of water plant production and pipe distribution, it is necessary to install additional handover accounting metering flow meters; In addition, the water plant needs to pay water resources fees to the state from collecting water from rivers free of charge, and it also needs to install additional flow meters. Therefore, the demand for large caliber handover accounting instruments in the water supply industry has increased significantly

in 2002/2003, the equipment working committee of China Urban Water Supply Association investigated the variety composition of flow meters installed in 46 large and medium-sized urban water supply enterprises in China (excluding impeller water meters). Among the 1900 flow meters installed in 46 enterprises, electromagnetic flowmeter was the most used, accounting for 61.9%, followed by ultrasonic flowmeter, accounting for 26.6%, plug-in flowmeter, 9.7%, and Venturi flowmeter, only 1.8%. Compared with the flowmeter used in the factory water of water plants investigated in 1991 in the "urban water supply 2000 technology development plan", the electromagnetic flowmeter increased a lot (55% in 1991), while the plug-in flowmeter decreased a lot (20% in 1991). Compared with the application of flow meters reported by Tokyo Metropolitan Waterworks Bureau in 2000 (1083 samples, 30.1% venturi differential pressure flowmeter, 45.2% electromagnetic flowmeter and 18.4% ultrasonic flowmeter), our electromagnetic flowmeter is more used, while venturi differential pressure flowmeter is less used. The venturi differential pressure instrument of Tokyo Metropolitan Waterworks Bureau is widely used in the handover measurement of finished water and incoming raw water and the internal flow control of water plants

evaluation of water supply enterprises on the flow instruments used

the long-term operation practice of domestic water supply enterprises on the various varieties of flow instruments used believes that: electromagnetic flowmeter has good performance, high accuracy, mature technology, and is recognized by most enterprises. Although the price is high, ultrasonic flowmeter will be more used in the future, with stable performance, medium accuracy, and multi-channel or pipe segment instruments are higher, The ultrasonic flowmeter with external clamping transducer can be installed without interruption of flow and service, which is its unique advantage. It is expected that due to its moderate price and convenient installation, it will have greater development space; Plug in turbine flowmeter has poor stability and accuracy, but its price is low. Under the condition of good maintenance and management, it is more suitable for small and medium-sized water plants in cities and towns; At present, only a few enterprises have installed venturi differential pressure flow meters. For example, dozens of Venturi differential pressure flow meters have been used in the Dongshen water supply project to deliver water to Hong Kong, which are generally of medium accuracy. The real flow calibration criteria can obtain high accuracy. It has the advantage that as long as the geometric dimensions of Venturi are measured to achieve regular inspection without real flow calibration, there is still a certain development space with the progress of technology

field comparison and verification of large diameter flow instruments

according to the requirements of ISO9000 quality management system, the measuring instruments must operate in a controlled state, and the provisions of jjg198-94 verification regulation of velocity flowmeter must be verified regularly. There are usually two methods to check the flow value of flow meter: offline inspection and on-site inspection. The off-line flow calibration check unloads the instrument from the pipeline and sends it to the laboratory flow calibration device for real flow calibration. However, the large diameter pipes in the water supply industry are not allowed to cut off the water flow at will, stop service, disassemble the flow sensor, and implement offline calibration, which is not easy to achieve due to the huge engineering cost. This problem became a hot topic of discussion at the "flow instrument application technology seminar" held by the equipment committee of China Water Conservancy Association in November 2003. In practice, each water supply enterprise explores several methods of on-site comparison or indirect inspection (check) according to their respective use conditions, verifying or evaluating that the flow measurement value of the flow meter still remains or has exceeded the original calibration accuracy level, as a basis for whether it can still be used or needs further inspection. Among the 24 papers proposed by 19 water supply companies, 11 involved the field comparison or verification of large-diameter flow instruments

real flow calibration of flow instruments is a group of operation processes to establish the relationship between the indicated value of the calibrated flow instrument and the corresponding value of the original standard or transfer standard. It is legal to transfer the calibrated value to the calibrated instrument; The on-site comparison is to compare the values with the instrument quantities of the same (or similar) accuracy level under the specified conditions, which is the model selection operation of Jinan testing machine factory without the legal nature of measurement; Verification is the recognition that the specified requirements have been met through inspection and the provision of objective evidence on site

the on-site comparison methods proposed in the symposium papers include the clean water tank volume method, the series pipe section instrument method, the external clamping (external sticking) transducer ultrasonic flowmeter method and the insertion turbine flowmeter method. The verification methods include the inspection and verification of the electromagnetic flowmeter

the volume comparison of clean water tank is a traditional method often used in the water supply industry. The advantages of large volume clean water tank in the water plant can be used to obtain high comparison accuracy. Three enterprises proposed to implement this method in the seminar, among which the paper of Changsha water supply company briefly described the implementation process and compared the data of measured examples. Carefully measure the geometric size of the pool, hoping to obtain a volume uncertainty of 0.2%; The water level difference of the inlet pool will exceed 1m after a long operation (more than a few hours) to reduce the impact of various operating errors. Under such operating conditions, the total uncertainty of the clean water pool comparison method is expected to be between 0.5% and 1%

it is very common to compare the flow by using portable external clamping transducer ultrasonic flowmeter in the water supply industry. 9 of the 11 enterprises that put forward the on-site comparison paper have adopted this method. This method can obtain the accuracy of medium ratio, but when using this method, the uncertainty of the measurement system composed of the ultrasonic flowmeter installed in the field should be evaluated. Because the system uncertainty, in addition to the accuracy of the ultrasonic flowmeter itself (0.5% - 1.5% of the flow rate), should also include the additional error caused by the measurement deviation of the flow area, sound path distance and sound path angle (for example, the measurement deviation of the pipe inner diameter is 0.5%, the additional error caused by the flow area is 1%; the installation deviation of the transducer spacing is 1%, the additional error is 1%; the 45 ° sound path angle deviation is 1 °, the additional error is 1.7%). The incoming flow is deflected by upstream deflectors (such as valves and elbows) and the insufficient straight pipe section forms velocity distribution distortion and additional errors caused by rotating flow. Generally speaking, the accuracy of the portable ultrasonic flowmeter is actually the accuracy of the measured flow rate. Do not misunderstand or be misled into thinking that it is the accuracy of the measured flow rate. The total uncertainty of the comparison method of portable ultrasonic flowmeter is between 2% and 5%. If the measurement geometry is rough or the exact flow area cannot be known (such as serious corrosion or accumulation on the inner wall), the system uncertainty even exceeds 5%. Most water supply enterprises have noticed the importance of comparing the installation location and pipe/installation size of portable ultrasonic flowmeter. For example, when Shijiazhuang water supply corporation newly designed the flowmeter well, the pipe section and space for installing the flowmeter should be reserved at the place where the measurement conditions of the instrument well are ideal. Some enterprises use portable ultrasonic flowmeter to measure and compare after setting up flowmeter, and record the data, so as to analyze whether there are changes in the compared fixed flowmeter in the future

it can also change the installation position or mode of the transducer of the portable ultrasonic flowmeter to detect the flow condition of the on-site pipe section. For example, move two transducers along the circumference of the tube and check the line average velocity at different positions. The maximum velocity may be the closest to the actual average velocity position, because the average velocity reading caused by the velocity distortion at the most asymmetric position is the smallest. This is the evaluation method recommended by all published experimental report arguments. Compare the flow velocity measured by the transducer installed according to the Z method and the V method. If there is a large difference between the two, it indicates that there is serious transverse flow, that is, there are signs of rotating flow. Attention should be paid to and measures should be taken

there are three papers proposing to implement the comparison method of series pipe section flow instruments. One DN800 and DN1200 electromagnetic flowmeter of Guangzhou water supply company has been used for five years, and the sending and receiving parties have disputes about the measurement accuracy of the instrument, so they are temporarily connected in series with the same caliber or different caliber electromagnetic flowmeter for long-term operation comparison. The difference is only 0.1% - 0.2%, and the dispute will be settled

Changchun Water Supply Company connected an electromagnetic flowmeter in series at the downstream of an ultrasonic flowmeter inserted into the tube wall with a fixed transducer for comparison. It was found that the ultrasonic flowmeter measured 8% less. Nanchang water supply company adopts the factory water pipeline to connect in series and install two electromagnetic flow meters for mutual comparison. If the difference between the measured values of the two meters is abnormal, it can be sent for inspection step by step. Once one instrument fails, the other works as usual, and there will be no disputes due to the interruption of measurement

two enterprises use the plug-in turbine flowmeter to compare the flow with the flowmeter in use with the fixed installation. Nanchang water supply company updated three flow meters in DN1000 pipeline, and reserved insertion holes and valves on one side to insert turbine flowmeter for regular flow comparison. The company believes that the turbine flowmeter can be used in a short time, with stable and reliable measured values, simple operation and low cost. Xiangfan water supply company updated the measuring point of the original plug-in turbine flowmeter into a pipe section flowmeter, retained the original plug-in installation port, and periodically inserted the turbine flowmeter for comparison in the future. Although the measurement accuracy of the large-diameter system composed of the plug-in flowmeter is low (2.5% - 5%), because even though the turbine flow sensor has high accuracy (0.5% - 1% of the flow rate), it also includes the measurement error of the flow area and the uncertainty of the flow velocity distribution coefficient/blockage coefficient, etc., it has excellent repeatability (0.25% - 0.5%). If the turbine flowmeter is regularly compared with the in-service flowmeter at the same position, and compared with the first comparison data after new installation, it can be evaluated whether the instrument operates normally and accurately

Shanghai water supply company/raw water company and Guangzhou water supply company explored the methods of on-site inspection and verification of electromagnetic flowmeter respectively. They used to check the resistance/insulation and excitation current of 10% sensor excitation coil with insufficient flow transmission to evaluate whether the magnetic field strength changed, measure the electrode liquid resistance to evaluate the electrode surface condition, check the insulation of each part to judge the deterioration degree of parts, etc, Check the converter with analog annunciator and other general instruments

verify whether the instrument maintains its original performance through these inspections. Over the past few years, Shanghai has accumulated experience in the inspection and verification of more than 300 sets, which is also showing uneven development in the industrial chain

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