Regarding the straight pipe sections before and after the flow meter

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Measurement is the eye of industrial production. Flow metering is one of the components of metrological science and technology, and it is closely related to the national economy, national defense construction, and scientific research. Flow metering is widely used in various fields such as industrial and agricultural production, national defense construction, scientific research, foreign trade, and people’s daily lives. Instruments that have requirements regarding the straight pipe section include the HKB target flow meter, HKE electromagnetic flow meter, HKGB vortex flow meter, Anubaa meters, and orifice plates; the typical requirement is 5 units in front of and 3 units behind the straight pipe section. Most HKE electromagnetic flowmeters nowadays use non-uniform electromagnetic fields, which require less axial symmetry in the fluid velocity distribution; as a result, the electromagnetic flowmeters can be made somewhat smaller ； On the other hand, vortex flow meters, Coriolis meters, and orifice plates have relatively strict requirements regarding the fluid velocity distribution; failure to meet the requirements for straight pipe sections may result in an inability to carry out measurements. At present, there is no practical empirical data regarding the impact on measurement accuracy and errors. If the measurement parameters are used for process control, errors within acceptable limits for that process are sufficient; however, if they are used for metering purposes, such as for water, natural gas, oil, etc., the required nominal accuracy must be achieved. Additionally, the measuring instruments used for metering are inspected by the metrology authorities, and those that do not meet the standards will not be approved. During the construction of the HKGB vortex flowmeter project, the requirements specified in the design were not followed; as a result, the required length of straight pipe section was not achieved. During the water-flow testing, the measurements showed significant errors – the readings were completely inaccurate. When 200 kilograms of water flowed through the system, the measured amount was 1100 kilograms. The problem was resolved after the straight pipe section was adjusted, and it’s clear now that the importance of having an adequate straight pipe section cannot be overstated. If possible, it is recommended to leave a longer straight pipe section. For typical orifice plates, the length is 10D in front and 5D behind; it can also be 24D in front and 7D behind. It is preferable that the straight pipe section ahead be 30–50D long. Flow rate, along with temperature, pressure, and level, are important parameters in general thermal and chemical production processes. These parameters are used to monitor and control the production process, thereby enabling its automation.