First, electromagnetic flowmeter
Electromagnetic flowmeter is a kind of flowmeter applying Faraday's law of electromagnetic induction. Its sensor is mainly composed of measuring tube lined with insulating material, penetrating a pair of electrodes installed on the measuring tube wall and a pair of coils and cores for generating working magnetic field. When the conductive fluid flows through the sensor measuring tube, a voltage signal proportional to the average flow velocity of the fluid is induced on the electrode. The signal is amplified by the converter, which directly displays the flow and the total amount and can output the analog digital signal. Figure 1
General electromagnetic flowmeters are used only for full-tube measurement of the flow of conductive fluids. Dalian DS Series Electromagnetic Flowmeters of this series have been applied to various domestic scenes and are well-received. Its biggest characteristic is: Electromagnetic flowmeter electrode contains Pt resistance temperature detection, used to correct the influence of volume temperature. This ensures the accuracy of the flowmeter. At present, the company is embarking on the development of non-full-tube electromagnetic flowmeters and flowmeters that measure lower electrolyte volumes. Non-full tube electromagnetic flowmeters need to measure the height of liquid in the tube. By using two excitation windings in forward and reverse series, respectively, two different magnetic field strengths and magnetic field distributions are generated to measure the flow signal potential, and the ratio between the potentials has a certain function relationship with the height of the liquid level. From this relationship, the height of the liquid level in the tube is calculated, the cross-sectional area of ​​the fluid is calculated, and the flow rate measured by the same method as the conventional electromagnetic flowmeter is multiplied to obtain the volumetric flow rate. Once a non-full-flow meter is invented, its application can be extended to the field of sewage discharge with free surface natural flow and improve the measurement accuracy in this area. The measurement error of conventional non-full pipe or open channel flow is reduced from ±(3~5)%FS with a trough meter to ±(1~2)%FS with an electromagnetic flowmeter. A flow meter for measuring lower electro-releasing liquid (referred to as an electrodeless electromagnetic flow meter) is a glycerin, ethylene glycol, or the like that cannot be measured using a flow meter. This type of instrument has almost no slurry noise and no-flow noise, and it does not generate noise caused by electrode surface effects. The inner surface of the lining is covered with a non-conductive layer such as grease or with a thin layer of insulative dirt that will not affect the measurement.
Another development direction of the electromagnetic flowmeter of Dalian Dayo Bosite Electronic Co., Ltd. is the development of low-power and two-wire electromagnetic flowmeters. The two-wire system does not require an additional external excitation circuit. Instead, it uses the 4mADC current to provide the required power for the instrument. It is usually anti-tens of milliwatts. Low-power electromagnetic flow meters will use dry batteries or solar cells, which will make it easier to use electromagnetic flow meters for places without mains power.
Dalian Ocean Sub-electronics plug-in electromagnetic flowmeter has been successfully trial-produced, so that the plug-in electromagnetic flowmeter is in an advantageous position in the application of large diameter, but also solve the problem of pressure-mounted electromagnetic flowmeter.
Another development direction of the electromagnetic flowmeter is the industrial shift to residential civilian areas. Reduce the electromagnetic flowmeter measurement accuracy to performance, such as the basic error of ± 2% (usually ± 0.2% ~ ± 1% for industrial use), designed to have the characteristics of water meter electromagnetic water meter. In Japan, this type of electromagnetic water meter has been incorporated into the Japanese water meter standard.
Second, the mass flow meter
The mass flowmeter uses the Coriolis principle, that is, the phase difference of the vibration frequency in the lower half of the measuring tube is proportional to the mass flow to measure the flow, and the density is obtained by using the function relationship between the resonant frequency of the measuring tube and the measured density of the medium in the tube. The volume flow qv(=qm/e) is derived from the mass flow qm and the density Ï of the two basic parameters. If the measured liquid is a mixture of two liquids with a certain density difference that is compatible or incompatible, a density calculation is used to obtain The concentration of a liquid in a mixture, such as the moisture content of a mixture of oil, water, and nail, can be measured in liquid-solid two-phase flow.
figure 2
The Coriolis mass flowmeter reduces accuracy (range error from ±0.2% to ±0.5%), functionality is reduced, and the price of design-pervasive instruments is only 50% to 70% of that of traditional Coriolis mass flowmeters. It also advances to lower prices.
Small liquid mass thermal flowmeter, its flow range 1 ~ 1000g / h, the basic error ± (0.5 ~ 1)% FS. At present, it is mainly used in experimental devices such as chemical, petrochemical and food industries. For example, the Flomtgn type from Brooks, USA, Liqui-Flow type and μ-Flow type micro flowmeters from Bronk Horst Hi-Tech in the Netherlands.
Thermal mass flowmeters are used for small gas flow measurements, and are used in flow measurement and control of hydrogen, oxygen, and ammonia in semiconductor industries, heat treatment furnaces, and analytical instruments, as well as in the measurement of leakage during valve manufacturing. The plug-in thermal flowmeters that have been selling well in recent years abroad are mainly used in large and medium-sized pipelines for environmental protection and process industries. Such as cement industry vertical mill discharge hot gas flow control.
Third, vortex flowmeter
The vortex frequency f separated by the vortex generating body of the vortex flowmeter is proportional to the flow velocity v (f=k1v, k1 is the coefficient) and is also subjected to the lift force F that is proportional to Ïv2 (F=k2Ïv2, Ï is the fluid density, and k2 is the coefficient). Dividing f by F and multiplying the area of ​​flow A, the mass flow qm can be obtained, ie
Qm=(F/f)A=(k2Ïv2/k1v)A=kÏvA
Where k is the meter factor, k=k2/k1
At present, the vortex flowmeter is equipped with a differential pressure transmitter and a temperature sensor to remove the measurement error caused by the pressure change and temperature, so that the measurement accuracy of the vortex flowmeter is greatly improved.
The LO-FLO Micro Vortex Flowmeter produced in the United States can measure the tiny flow with an accuracy of ±0.5%, and the measured pipe position can be several millimeters.
At present, the market price of vortex flowmeters tends to mature.
Fourth, ultrasonic flowmeter
1, time difference type ultrasonic flowmeter
The working principle is that when the ultrasonic wave propagates in the liquid, the flow of the liquid will cause a slight change in the propagation time, and the change of the propagation time is proportional to the flow velocity of the liquid.
Its mathematical expression:
The development of Dalian Dayosite DS time-lapse ultrasonic flowmeter can be divided into three stages according to the installation method, namely the installation phase of the external clamp, the phase of the plug-in installation and the phase of the flanged installation. The three phases of products complement each other, meet the needs of different users on the spot, and solve problems at different sites. The external clamp type ultrasonic flowmeter is irreplaceable for flow inspection, tracking acquisition, flow balance, leak detection, crude fault diagnosis of fluid equipment, edible, medical liquids, chemical water, and desalinated water. The plug-in type ultrasonic flowmeter solves the problem that the pipelines are irregular, thick and rusty, and can not be solved by clamps. At the same time, they can be installed with pressure and stop production. Especially for large pipelines is a very economical option. Insertion type ultrasonic flowmeter is not easy to move due to the fixed installation of the sensor, reducing the installation error, its accuracy can reach ± ​​0.5%, the advantage of the flange type ultrasonic flow meter is the installation of peace of mind, its precision is higher, up to ± 0.2%.
Time-difference ultrasonic flowmeter can not only measure the fluid flow rate and flow, but also use the difference of speed of sound in different liquids to identify the liquid type in the pipeline (such as Dalian Sunburst DS ultrasonic flowmeter). Currently, low-power ultrasonic flow meters have been used in the market (power <2W)
Ultrasonic water meter developed by Dalian Dayo Bosite Electronics Co., Ltd. will be introduced to the market by the end of June to further expand the market for ultrasound. With the declining prices, its battery-powered ultrasonic water meters will be used in practical areas of residential dwellings, in addition to non-powered sites.
2, Doppler ultrasonic flowmeter
The principle of operation is that there is a discontinuous perturbation of any flowing liquid within the fluid conduit. Discontinuous perturbations can be suspended solid particles, bubbles or interfaces due to fluid disturbances that generate reflected ultrasonic waves. Shift Δf, frequency shift Δf is a linear function of flow rate. By measuring the frequency shift Δf, the flow rate (or flow) in the pipeline can be measured.
With the advancement of technology, the development of Doppler ultrasonic flowmeters can measure not only dirty liquids with suspended particles and bubbles, but also pure fluids. Ocean Primary DS Doppler flow meter has this feature.
The market price of Pooler Ultrasonic Flowmeter is relatively stable, with no major changes in the short term.
3, ultrasonic gas flowmeter
In recent years, it has been used in fields such as steam, storage transfer and accounting, and civil residential gas consumption measurement. Ultrasonic flow meters for gas use ultrasonics to have low propagation efficiency between solid and gas interfaces. It is difficult to transmit sufficient acoustic energy through the wall of a pipe with an externally mounted transducer. Currently, most ultrasonic transducers extend into the pipeline directly to the gas. Launch and receive sound waves from the gas. Gas flow meters are mostly composed of ultrasonic flow sensors, but there are also plug-in type converters installed in the structure of the pipeline to be measured.
At present, foreign energy development, natural gas is developing faster than petroleum, and has promoted the development of gas ultrasonic flowmeters that have been slow to develop in the past. The gas ultrasonic flowmeter has the advantages of no pressure loss compared with traditional gas turbine flowmeters and gas displacement flowmeters. It saves considerable pumping costs and has no moving parts. Therefore, it has developed rapidly in the natural gas industry. . Ultrasonic gas flow meters measure superheated steam up to 480°C.
to sum up
With the development of the industry and the gradual maturity of the market, the application of ultrasonic flowmeters will become more and more extensive, and it will be more comprehensive and extensive in the fields of custody transfer and financial and trade accounting applications. Its superior performance has been recognized by various parties. With the full development of the market, the market adjustment of its prices will become more reasonable. In addition, the application of electromagnetic flow meters will have a market share for a long time. Mass flow meters and vortex flowmeters are a perfect complement to the flow meter market. However, due to its own shortcomings (such as large errors, etc.), such as orifice flow meters are gradually out of the market.
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