Flowmeter selection principles

HG/T 20507-2000 Automation Instrument Selection and Design Regulations http://bbs.hcbbs.com/thread-51211-1-1.html

It is believed that the priority of selection is: 1. Be able to measure the parameters required by the process, including accuracy 2. Choose the one with the least amount of maintenance based on the first point. 3. Choose the one with the most economical one-time investment based on the first two points. 4. You can have special preferences.

Of course, there are other factors to consider, including first, the measurement method is reliable, that is, the sampling device will not cause mechanical strength or electrical circuit failures during operation, causing accidents.； Second, the measuring instruments will not affect the safety of the production system regardless of normal production or failure. For example, for the measurement of high-temperature and high-pressure main steam flow in power plants, the primary measuring element installed in the pipeline must be firm to ensure that no mechanical damage occurs under the erosion of high-speed steam flow. Therefore, standard throttling devices are generally preferred over non-standard speed measurement devices such as cantilever-type double trumpet tubes or insertion flow meters, as well as target type and turbine flow meters with low structural strength. For fuel-fired power plants and places with flammable gases, explosion-proof instruments should be used. 2. Correctly selecting the specifications of the instrument is also an important part of ensuring the service life and accuracy of the instrument. Special attention should be paid to the selection of static pressure and temperature resistance. The static pressure of the instrument is the pressure resistance level. It should be slightly greater than the working pressure of the medium being measured, generally 1.25 times, to ensure that no leakage or accident occurs. The choice of measurement range is mainly the choice of the upper limit of the instrument scale. If you choose a small one, it will be easily overloaded and damage the instrument. ； If it is too large, it will hinder the accuracy of the measurement. Generally, it is selected as 1.2 to 1.3 times the maximum flow value in actual operation. 3. For long-term contact instruments installed on production pipelines, the energy loss caused by the flow measurement components should also be considered. Under normal circumstances, multiple measuring elements with large pressure losses, such as throttling elements, etc., should not be used in the same production pipeline. 4. Prices are arranged from low to high according to the same caliber and price. Measurement liquid glass rotor flowmeter orifice plate oval gear flowmeter turbine flowmeter metal rotor flowmeter electromagnetic flowmeter vortex flowmeter ultrasonic flowmeter mass flow meter measurement gas glass rotor flowmeter orifice plate metal rotor flowmeter turbine flowmeter vortex flowmeter

There is also an Annubar (average pitot tube) with an accuracy of 0.75%. The front groove is slotted to improve the average effect of pressure taking. It also has an integrated temperature measurement for easy maintenance.

flow meter: 1. Different measurement levels, control levels, and general displays. 2. Party A’s requirements for cost control. 3. According to the parameters provided by the process. 4. On-site maintenance volume, etc.! 5. Online replacement, etc.!

Flow meter selection refers to the production requirements, starting from the actual situation of instrument product supply, comprehensively considering the safety, accuracy and economy of measurement, and determining the flow sampling device method and the type and specification of the measuring instrument based on the properties and flow conditions of the fluid to be measured. The safety and reliability of flow measurement, first of all, is the reliability of the measurement method, that is, the sampling device will not cause mechanical strength or electrical circuit failures during operation, causing accidents. ； Second, the measuring instruments will not affect the safety of the production system regardless of normal production or failure. For example, for the measurement of high-temperature and high-pressure main steam flow in power plants, the primary measuring element installed in the pipeline must be firm to ensure that no mechanical damage occurs under the erosion of high-speed steam flow. Therefore, standard throttling devices are generally preferred over non-standard speed measurement devices such as cantilever-type double trumpet tubes or insertion flow meters, as well as target type and turbine flow meters with low structural strength. For fuel-fired power plants and places with flammable gases, explosion-proof instruments should be used. On the basis of ensuring the safe operation of the instrument, we strive to improve the accuracy and energy saving of the instrument. For this reason, it is not only necessary to select a display instrument that meets the accuracy requirements, but also to select a reasonable measurement method based on the characteristics of the medium being measured. Main steam flow measurement in power plants, because it is crucial to the safety and economy of the power plant, generally uses mature standard throttling devices equipped with differential pressure flowmeters. Sewage and fuel in chemical water treatment are dirty flows and low Reynolds number viscous flows respectively, and standard throttling devices are not suitable. For dirty flows, non-standard throttling parts such as round orifice plates are generally used with differential pressure meters or ultrasonic Doppler flowmeters, while for viscous flows, volumetric, target or wedge-shaped flowmeters can be used respectively. The water volume at the entrance of the turbine, the circulating water volume in the condenser and the regenerated steam of the recuperation unit are all flow measurement parameters for large pipe diameters (above 400mm). Due to the difficulty in processing and large pressure loss, standard throttling devices are generally not used. According to the characteristics of the medium to be measured and the measurement accuracy requirements, insertion flow meters, velocity measuring components with differential pressure meters, ultrasonic flow meters are used, or non-destructive methods such as marking methods and simulation methods are used to measure flow rates. In order to ensure the service life and accuracy of the flow meter, the anti-vibration requirements of the instrument should also be paid attention to when selecting the type. In hot and humid areas, humid and heat instruments should be selected. Correctly selecting the specifications of the instrument is also an important part of ensuring the service life and accuracy of the instrument. Special attention should be paid to the selection of static pressure and temperature resistance. The static pressure of the instrument is the pressure resistance level. It should be slightly greater than the working pressure of the medium being measured, generally 1.25 times, to ensure that no leakage or accident occurs. The choice of measurement range is mainly the choice of the upper limit of the instrument scale. If you choose a small one, it will be easily overloaded and damage the instrument. ； If it is too large, it will hinder the accuracy of the measurement. Generally, it is selected as 1.2 to 1.3 times the maximum flow value in actual operation. For contact instruments installed on production pipelines that run for a long time, the energy loss caused by the flow measurement element should also be considered. Generally speaking, multiple measuring elements with large pressure losses, such as throttling elements, should not be used in the same production pipeline. In short, no measurement method or flow meter can adapt to various fluids and flow conditions. Different measurement methods and structures require different measurement operations, usage methods and usage conditions. Each type has its own unique advantages and disadvantages. Therefore, the best model that is suitable for production requirements, reliable, economical and durable should be selected based on a comprehensive comparison of various measurement methods and instrument characteristics.