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Flow meter classification and working principle introduction

One. Classification of flow meters
According to the measurement principle, there are: mechanical principle, thermal principle, acoustic principle, electrical principle, optical principle, atomic physics principle and so on.
According to the structural principle of the flowmeter, it is divided into: volumetric flowmeter, differential pressure flowmeter, float flowmeter, turbine flowmeter, electromagnetic flowmeter, vortex flowmeter in fluid oscillation flowmeter, mass flowmeter And plug-in flow meters, probe flow meters.
two. Working principle and application of common flowmeter
Differential pressure flowmeter
The differential pressure flowmeter is a meter that calculates the flow rate based on the differential pressure generated by the flow detecting member installed in the pipe, the known fluid condition, and the collective size of the detecting member and the pipe.
Application: Differential pressure flowmeter has a wide range of applications. Various objects are used in flow measurement of closed pipelines, such as fluid: single phase, mixed phase, clean, dirty, viscous flow, etc.; work: atmospheric pressure, High pressure, vacuum, normal temperature, high temperature, low temperature, etc.; pipe diameter: from a few millimeters to several meters; flow: subsonic, sonic, pulsating flow. Its use in various industrial sectors accounts for about 1/4 to 1/3 of the total flow meter.
2. Float flowmeter
The float flowmeter, also known as the rotameter, is a variable-area flowmeter. In a vertical cone that is enlarged from the bottom to the top, the gravity of the circular cross-section float is absorbed by the liquid power, so that the float can Freely rise and fall within the cone.
Application: The float flowmeter is the most widely used type of flowmeter after the differential pressure flowmeter, especially in small and microflow.
3. Volumetric flowmeter
The volumetric flowmeter, also known as the fixed displacement flowmeter, referred to as the PD flowmeter, is the most accurate class in the flowmeter. It uses mechanical measuring components to continuously divide the fluid into a single known volume fraction, according to the measurement. The chamber repeatedly fills and discharges the volume of the volume of the fluid one by one to measure the total volume of the fluid.
Application: Positive displacement flowmeters and differential pressure flowmeters and float flowmeters are listed as the three types of flowmeters with the largest usage. They are often used for the total measurement of expensive media (oil, natural gas, etc.).
4. Turbine flowmeter
The turbine flow meter is the main type of speed flow meter. It uses a multi-blade rotor (turbine) to sense the average flow rate of the fluid, and derives the flow or total amount of the meter. Generally, it consists of two parts, a sensor and a display instrument, and can also be made into a unitary type.
Applications: Turbine flow meters are widely used in the measurement of petroleum, organic liquids, inorganic liquids, liquefied gases, natural gas and cryogenic fluids.
5. Electromagnetic flowmeter
The electromagnetic flowmeter is a meter for measuring conductive liquids according to Faraday's law of electromagnetic induction.
Application: Electromagnetic flowmeters have a series of excellent characteristics that can solve the problems that other flowmeters are not easy to apply, such as the measurement of dirty flow and corrosion flow. Electromagnetic flowmeters are widely used in applications. Large-diameter instruments are widely used in water supply and drainage projects. Small and medium-sized calibers are often used in high-demand or difficult-to-measure applications, such as steel industry blast furnace tuyere cooling water control, paper industry measuring pulp and black liquor, and strong chemical industry. Corrosive liquid, pulp of non-ferrous metallurgical industry; small caliber, small caliber is often used in places where there are hygienic requirements in the pharmaceutical industry, food industry, biochemistry, etc.
6. Vortex flowmeter
The vortex flowmeter is a non-streamlined vortex generator placed in the fluid, and the fluid is alternately separated on both sides of the generator to release two strings of regularly staggered vortex. When passing through the flow section, the flow rate is proportional to the volumetric flow. Therefore, the flow rate can be measured by measuring the oscillation frequency.
Application: The vortex flowmeter has developed rapidly and has become a general-purpose flowmeter.
7. Ultrasonic flowmeter
The ultrasonic flowmeter is designed based on the geometrical principle that the velocity of the ultrasonic wave propagating in the flowing medium is equal to the average flow velocity of the measured medium and the velocity of the acoustic wave itself. It is also measured by the flow rate to reflect the flow rate. Ultrasonic flowmeters can be divided into time difference type and Doppler type according to the measurement principle.
Application: The propagation time method is applied to clean, single-phase liquids and gases. Typical applications include factory effluent, strange liquid, liquefied natural gas, etc.; gas applications have been well used in the field of high pressure natural gas; Doppler method is suitable for two-phase fluids with less heterogeneous content, such as untreated sewage, Factory effluent, dirty process fluids, usually not suitable for very clean liquids.
8. Mass flow meter
Mass flow meters are available in both direct and indirect versions. The direct mass flow meter uses the principle directly related to the mass flow rate to measure; the indirect mass flow meter uses the density meter to indirectly multiply the volume flow rate to obtain the mass flow rate.
Application: In the case of high temperature and high pressure in modern industrial production, the application of direct mass flowmeters is difficult due to material and structure, while the indirect mass flowmeter is limited by the range of humidity and pressure. It is also not practical.
9. Plug-in flow meter
The working principle of the plug-in flowmeter is based on Faraday's law of electromagnetic induction. In the electromagnetic flowmeter, the conductive medium in the measuring tube is equivalent to the conductive metal rod in the Faraday test, and the two electromagnetic coils at the upper and lower ends generate a constant magnetic field. When a conductive medium flows, an induced voltage is generated. The two electrodes inside the pipe measure the induced voltage generated. The measuring tube is electromagnetically isolated from the fluid and the measuring electrode by a non-conductive inner liner (rubber, Teflon, etc.).
Applications: power generation and cogeneration, heating industry; aviation, aerospace, shipbuilding, nuclear and weapons industries; machinery, metallurgy, coal mining and automobile manufacturing; petroleum, chemical industry; pharmaceutical, food and smoke manufacturing industries; Farming and light industry.
10. Probe flowmeter
The basic principle of the probe flowmeter is to conduct the total static pressure through the probe hole and the pressure guiding tube to the differential pressure and pressure sensor. As long as the probe hole is not blocked, even if there is debris or dirt, the pressure can be accurately transmitted. Does not affect the accuracy. Since the medium in the pressure guiding tube does not flow, the foreign matter is difficult to enter and block, so that high precision can be maintained for a long time.
Application: A wide range of applications. First, a wide range of applicable media: can measure water vapor (saturation, overheating), air, gas, natural gas, various chemical materials gas, liquid, water, various solutions, oil, etc.; medium temperature can be up to 650 degrees Celsius, the highest pressure Allow 25Mpa. Second, the applicable flow range is wide: the medium flow rate can be measured at a minimum of 0.1 tons/hour, and the maximum can be measured at 5000 tons/hour. Third, it is applicable to a wide range of cross-section shapes of the medium pipe: the flowmeter does not require the geometry of the cross section of the medium pipe, such as a circular shape, an elliptical shape, a square shape, a rectangular shape, a diamond shape, and the like.

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