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Industry Information
Flowmeter selection attention to four points
2011-6-6 18:14:11

As the main flowmeter production and sales manufacturer, Jinhu Dongxiang Meter Co., Ltd.'s flowmeter and meter business department concluded that there are 4 points to be grasped when selecting the flowmeter .

Dongxiang Instrument Flowmeter Division summarizes four main selection points through years of sales and production experience and customer feedback. The selection of flowmeters should generally be considered from these four points. The nature and flow conditions determine the method of flow sampling device and the type and specifications of the measuring instrument. The selection must fully meet the instrument conditions provided by the process, considering the accuracy level and economy, and considering the safety of the measurement.

1. Determine the type and specification of the flow meter according to the nature and flow of the fluid to be measured. The nature and flow of the fluid determine the form and specifications of the flow meter . First of all, you must consider several key physical and chemical properties of the fluid: the state of the fluid (solid or gaseous or liquid), the conductivity of the fluid, the chemical corrosion of the fluid, and the viscosity of the fluid. Secondly, we must fully understand the application scope of various forms of flow meters. In the selection, the physical and chemical characteristics of the fluid should be comprehensively considered. The fluid in solid state is generally dust or bulky. There are only three types of flowmeters: impulse flowmeter, belt scale and track scale. There are many types of flow meters for liquid and gaseous fluids. Generally, flow meters have series and models dedicated to gas measurement. For example, the Coriolis force flow meters we use have series models dedicated to gas measurement. In the case of relatively poor liquid conditions, it does not call out corrosion, is conductive, and has solid particles. In this case, it is best to choose an electromagnetic flowmeter. The flowmeters suitable for high viscosity reading mainly include oval gear flowmeters, waist flowmeters, scraper flowmeters, target flowmeters, wedge-shaped flowmeters, etc., which are determined according to accuracy, economic requirements and other actual working conditions. . Finally, when selecting a fluid with corrosion, you must pay attention to the selection of the material of the flowmeter. For example, when the electromagnetic flowmeter is used to measure hydrochloric acid liquid, the electrode must be a tantalum electrode, otherwise the electrode is easily corroded.

2. The choice of flow meter must fully consider the meter conditions provided by the process. First, the static pressure and temperature of the medium must be considered. The static pressure and temperature resistance of the flow meter are also an important part to ensure the service life and accuracy of the meter. The static pressure of the meter is Withstand pressure, it should be slightly greater than the working pressure of the measured medium, generally 1.25 times to ensure that no leakage or accident occurs. The second is the choice of the measuring range, mainly the choice of the upper limit of the meter scale. If you choose a small size, it is easy to overload and damage the meter; if you choose a large size, it will hinder the accuracy of the measurement. National standards stipulate that the maximum flow rate does not exceed 95% of full scale; the normal flow rate is 70% to 85% of full scale; and the minimum flow rate is not less than 30% of full scale. Finally, the most important instrument condition is the process tube diameter. Some flowmeters are not particularly large. Some large diameter flowmeters are very expensive. At present, more suitable flowmeters with large diameters include flute-shaped uniform velocity tubes, plug-in vortices, and inserts. Turbine, electromagnetic flowmeter, venturi, ultrasonic flowmeter.

3. Considering the accuracy grade and economics of the flow meter, the accuracy grade of the flow meter must comply with the provisions of the National Economic Commission [1983] No. 244 "Requirements for Accuracy of Energy Measurement Instruments". Generally, the places with high requirements for accuracy include the measurement of raw materials entering the plant and the production equipment, the measurement of the finished products exiting the device and the factory sales, the measurement of raw materials for the process formula, and the measurement of expensive materials. For the general reference flow in the production equipment, generally cheaper flowmeters such as glass rotors and metal rotors are selected. Vortex joint flowmeters are commonly used for gas (air, nitrogen, and steam) on public works in production. Electromagnetic flowmeters are used for various types of water. These two options are economical and can meet the accuracy requirements.

4. Considering the safety of measurement, the safety and reliability of flow measurement, the first is the reliable measurement method, that is, the sampling device will not cause accidents caused by mechanical strength or electrical circuit failure during the operation; the second is whether the measuring instrument is in normal production or fault conditions It will not affect the safety of the production system. For example, for the measurement of high-temperature and high-pressure main steam flow in a power plant, the primary measurement element installed in the pipeline must be firm to ensure that no mechanical damage occurs under the high-speed steam flow. Therefore, it is generally preferred to use standard throttling devices instead of non-standard speed measuring devices such as cantilever beam double horn tubes or plug-in flow meters , and target-type and turbine flow meters with low structural strength. For oil-fired power plants and flammable gas, explosion-proof instruments should be selected.