Instruments that measure fluid flow are collectively referred to as flow meters or flow meters. The flow meter is one of the important instruments in industrial measurement. With the development of industrial production, the accuracy and range of flow measurement requirements are getting higher and higher, and the flow measurement technology is changing with each passing day. Various types of flow meters have been introduced to suit various applications. More than 100 flow meters are currently in use.
Each product has its specific applicability and its limitations. According to the measurement principle, there are mechanical principles, thermal principles, acoustic principles, electrical principles, optical principles, and atomic physics principles.
Classification according to the structural principle of the flowmeter. There are volumetric flowmeters, differential pressure flowmeters, float flowmeters, turbine flowmeters, electromagnetic flowmeters, vortex flowmeters in fluid oscillating flowmeters, mass flowmeters and plug-in flowmeters.
According to the measurement object, there are two types of closed pipelines and open channels; according to the measurement purpose, it can be divided into total measurement and flow measurement. The meters are called the total meter and the flow meter. The total meter measures the flow through the pipeline over a period of time. It is expressed as the quotient of the total amount of flow over a short period of time divided by the time. In fact, the flowmeter is usually equipped with a cumulative flow device for use as a total meter. The meter is also equipped with a traffic transmitter. Therefore, it is no practical to divide the flowmeter and the total meter in a strict sense.
First, according to the principle of measurement
1. Mechanics: Instruments belonging to such principles have differential pressure and rotor type using Bernoulli's theorem; impulse type and movable tube type using momentum theorem; direct mass type using Newton's second law; using fluid momentum The target type of the principle; the turbine type using the angular momentum theorem; the vortex type using the principle of fluid oscillation, the vortex type; the pitot tube type using the total static pressure difference, and the volumetric type, the enthalpy, the trough type and the like.
2. Electrical Principles: The instruments used for such principles are electromagnetic, differential capacitive, inductive, strain resistant, etc.
3. Acoustic principle: ultrasonic measurement using the principle of acoustics for flow measurement. Acoustic (shock wave) and the like.
4. Thermal principle: The thermal method is used to measure the flow rate of the heat, direct calorimetry, indirect calorimetry and so on.
5. Optical principle: Laser type, photoelectric type, etc. are instruments that belong to this principle.
6. Originally based on physical principles: nuclear magnetic resonance, nuclear radiation, etc. are instruments of this type.
7. Other principles: Marking principle (trace principle, NMR principle), related principles, etc.
Second, according to the flowmeter structure principle classification
According to the actual situation of the current flowmeter products, according to the structural principle of the flowmeter, it can be roughly classified into the following types:
1 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 geometrical dimensions of the detecting member and the pipe.
The differential pressure flowmeter consists of a primary device (detection member) and a secondary device (differential pressure conversion and flow display instrument). Differential pressure flowmeters are usually classified in the form of test pieces, such as orifice flowmeters, venturi flowmeters, and uniform velocity flowmeters.
The secondary device is a variety of mechanical, electronic, electromechanical integrated differential pressure gauges, differential pressure transmitters and flow display instruments. It has developed into a large-scale instrument with a high degree of variety (series, generalization and standardization) and various types and specifications. It can measure flow parameters as well as other parameters (such as pressure, level, density, etc.). ).
The detection parts of the differential pressure flowmeter can be divided into three types according to the principle of action: throttling device, hydraulic resistance type, centrifugal type, dynamic pressure head type, dynamic pressure head gain type and jet type.
Test pieces can be divided into two categories according to their standardization: standard and non-standard.
The so-called standard test piece is designed, manufactured, installed and used according to the standard documents, and the flow value and the estimated measurement error can be determined without actual flow calibration.
Non-standard test pieces are those that are less mature and have not been included in the international standard.
The differential pressure flowmeter is one of the most widely used flowmeters, and its usage is the highest among all types of flowmeters. In recent years, due to the advent of various new flowmeters, its percentage of usage has gradually decreased, but it is still the most important type of flowmeter.
advantage:
(1) The most widely used orifice plate type flowmeter has firm structure, stable and reliable performance and long service life;
(2) A wide range of applications, so far no class of flowmeters can be compared;
(3) The detecting parts, transmitters and display instruments are produced by different manufacturers, which is convenient for economies of scale.
Disadvantages:
(1) Measurement accuracy is generally low;
(2) The range is narrow, generally only 3:1~4:1;
(3) The requirements for on-site installation are high;
(4) Large pressure loss (refer to orifice plate, nozzle, etc.).
Application overview:
Differential pressure flowmeters are widely used in a wide range of applications in flow measurement of closed pipes, such as fluids: single phase, miscible, clean, dirty, viscous flow, etc.; working conditions: atmospheric pressure, high pressure , vacuum, normal temperature, high temperature, low temperature, etc.; pipe diameter: from a few mm to a few m; flow conditions: subsonic, sonic, pulsating flow. Its use in various industrial sectors accounts for about 1/4 to 1/3 of the total flow meter.
2-hole plate flowmeter
advantage:
The standard throttle is universally available and approved by the International Standards Organization. It can be used without actual flow calibration and is unique in flow meters. The structure is easy to copy, simple, firm, stable and reliable, and low in price;
Wide range of applications, including all single-phase fluids (liquid, gas, steam), partial mixed-phase flow, general production process, diameter, working conditions (temperature, pressure) are products.
The test piece and the differential pressure display instrument can be produced separately from different manufacturers, and then produced in a professional scale;
Disadvantages:
The repeatability and accuracy of the measurement are moderate in the flowmeter, and the accuracy is difficult to improve due to the intricacies of many factors. The range is narrow, and since the flow coefficient is related to the Reynolds number, the general range is only 3:1 to 4:1. There is a long straight pipe length requirement, which is generally difficult to meet. Especially for larger pipe diameters, the problem is more prominent; the pressure loss is large; usually to maintain the normal operation of one orifice flowmeter, the pump needs additional power to overcome the pressure loss of the orifice plate. This additional power consumption can be directly
Pressure loss and flow calculations are determined. It takes about tens of thousands of kWh of electricity a year, equivalent to tens of thousands of yuan. The orifice plates are listed at normal pressure in the table below.
Energy consumption calculation results in the case of loss. The operating days are calculated based on three hundred and fifty days, and the electricity price is calculated at 0.35 yuan/kWh. It can be seen from the calculation of the power consumption data in the table that the additional operating cost of the orifice plate is extremely high, and the operating cost of the curved pipe flow meter is zero!
The orifice plate is sharply angled to ensure accuracy, so it is sensitive to corrosion, abrasion, scaling and dirt. It is difficult to guarantee the long-term use accuracy. It is necessary to remove the strong inspection once a year. The use of flange connection is prone to run, run, drip, and leak problems, greatly increasing the maintenance workload.
3 float flowmeter
The float flowmeter, also known as the rotameter, is a variable area flowmeter. In a vertical cone that is enlarged from bottom to top, the gravity of the circular cross section of the float is absorbed by the liquid power, thereby making the float It can rise and fall freely inside the cone.
The float flowmeter is the most widely used type of flowmeter after the differential pressure flowmeter, and it plays an important role in small and microflow.
In the mid-1980s, sales in Japan, Western Europe, and the United States accounted for 15% to 20% of flow meters. China's output in 1990 is estimated to be between 12 and 140,000 units, of which more than 95% are glass cone tube float flowmeters.
Features:
(1) Glass cone tube float flowmeter has simple structure and convenient use. The disadvantage is low pressure resistance and large risk of fragile glass tube; (2) Suitable for small pipe diameter and low flow rate;
(3) The pressure loss is low.
4 volumetric flowmeter
Volumetric flowmeters, also known as fixed displacement flowmeters, referred to as PD flowmeters, are among the most accurate in flowmeters. It utilizes a mechanical measuring element to continuously divide the fluid into a single known volume portion, and measures the total volume of the fluid based on the number of times the measuring chamber repeatedly fills and discharges the volume of the fluid one by one.
Volumetric flowmeters are classified into elliptical gear flowmeters, scraper flowmeters, dual-rotor flowmeters, rotary piston flowmeters, reciprocating piston flowmeters, disk flowmeters, and liquid-sealed rotary flowmeters. , wet gas meter and membrane gas meter.
advantage:
(1) High measurement accuracy;
(2) Installation pipeline conditions have no effect on the measurement accuracy;
(3) It can be used for the measurement of high viscosity liquids;
(4) The range is wide;
(5) Direct-reading instruments can be directly accumulated without external energy, and the total amount is clear and easy to operate.
Disadvantages:
(1) The results are complex and bulky;
(2) The type of the tested medium, the caliber, and the working state of the medium are more limited;
(3) Not suitable for high and low temperature applications;
(4) Most instruments are only suitable for clean single-phase fluids;
(5) Noise and vibration are generated.
Application overview:
The volumetric flowmeter and the differential pressure flowmeter and the float flowmeter are listed as the three types of flowmeters with the largest usage, and are often used for the total measurement of expensive media (oil, natural gas, etc.).
In recent years, the sales volume of PD flowmeters (excluding domestic gas meters and household water meters) in industrialized countries accounted for 13%~23% of flow meters; China accounted for about 20%, and production in 1990 (excluding household gas meters) was estimated at 340,000. The table, in which the oval gear type and the waist wheel type account for about 70% and 20% respectively.
5 types of sewage flowmeter
Sewage flowmeters are classified according to the principle of measurement:
1. The flowmeter has a throttle flowmeter, a bi-managed flowmeter, a uniform velocity flowmeter, a rotameter, and a target flowmeter. These flowmeters use the Bernoulli equation principle to measure the flow by measuring the fluid differential pressure signal. ;
2. The flowmeter has a turbine flowmeter, a vortex flowmeter, an electromagnetic flowmeter, a Doppler ultrasonic flowmeter, and a hotline velocity measuring flowmeter, which measure the flow rate by measuring the fluid flow rate;
3. The flow meter has a gear type flow meter, a scraper type flow meter, and a rotary piston type flow meter. These are measured by measuring a small volume of a standard volume to reflect the flow rate;
4. The flowmeter has a thermal mass flowmeter, a differential pressure mass flowmeter, an impeller mass flowmeter, a Coriolis mass flowmeter, and an indirect mass flowmeter, which reflect the flow by measuring the fluid mass;
5. The flowmeter has a gutter type flowmeter, which measures the flow rate by measuring the liquid level.
Sewage flow meter features:
1. The sewage flowmeter has a simple structure, firm and reliable, and long service life.
2. There are no moving parts and resistance parts in the measuring tube, no pressure loss, no blocking, reliable measurement, strong anti-interference ability, small size, light weight, convenient installation, small maintenance, wide measuring range, and measurement without fluid temperature and density. The effects of changes in pressure, viscosity, conductivity, etc. can be modified and installed on the old pipeline, with simple construction and installation, and small amount of engineering.
6 turbine flowmeter
Turbine flow meters, the main type of velocity flowmeters, use a multi-blade rotor (turbine) to sense the average flow rate of the fluid, and derive the flow or total amount of meters.
Generally, it consists of two parts, a sensor and a display, and can also be made into a unitary type.
Turbine flowmeters and volumetric flowmeters, Coriolis mass flowmeters are called three types of repeatable and accurate products in flowmeters. As one of the ten types of flowmeters, their products have developed into many varieties and more. The scale of series mass production.
advantage:
(1) High precision, among all flow meters, is the most accurate flow meter;
(2) good repeatability;
(3) Yuan zero drift, good anti-interference ability;
(4) The range is wide;
(5) Compact structure.
Disadvantages:
(1) The calibration characteristics cannot be maintained for a long time;
(2) Fluid properties have a large impact on flow characteristics.
Application overview:
Turbine flow meters are widely used in some of the following measurement objects: petroleum, organic liquids, inorganic liquids, liquefied gases, natural gas, and low temperature streams.
In Europe and the United States, turbine flowmeters are the natural meter after the orifice flowmeter. In the Netherlands alone, more than 2,600 gas turbines of various sizes and pressures from 0.8 to 6.5 MPa are used on natural gas pipelines. Flow meters, they have become excellent natural gas meters.
7 vortex flowmeter (USF)
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 the flow cross section is constant, the flow rate is proportional to the flow volume of the pilot volume. Therefore, the flow rate can be measured by measuring the oscillation frequency. Vortex flowmeters can be classified into stress type, strain type, capacitive type, thermal type, vibrating type, photoelectric type and ultrasonic type according to the frequency detection mode. This flowmeter was developed and developed in the 1970s. Because it combines the advantages of non-rotating components and pulsed digital output, it has a promising future.
advantage
(1) The vortex flowmeter has no moving parts, and the measuring component has a simple structure, reliable performance and long service life.
(2) The vortex flowmeter has a wide measuring range. The turndown ratio can generally reach 1:10.
(3) The volume flow of the vortex flowmeter is not affected by thermal parameters such as temperature, pressure, density or viscosity of the fluid being measured. Generally no separate calibration is required. It measures the flow of liquids, gases or vapors.
(4) It causes little pressure loss.
(5) High accuracy, repeatability of 0.5%, and low maintenance.
Disadvantage
(1) The volume flow rate of the vortex flowmeter is not affected by the thermal parameters such as temperature, pressure and density of the fluid to be measured, but the final measurement result of the liquid or steam should be the mass flow. For the gas, the final measurement result should be Is the standard volume flow. Mass flow or standard volume flow must be converted by fluid density, and fluid density changes due to changes in fluid conditions must be considered.
(2) The main factors causing the flow measurement error are: the measurement error caused by the uneven flow velocity; the medium density when the fluid condition changes can not be accurately determined; the wet saturated steam is assumed to be dry saturated steam for measurement. If these errors are not limited or eliminated, the total measurement error of the vortex flowmeter will be large.
(3) Poor anti-vibration performance. External vibrations can cause measurement errors in the vortex flowmeter and may not even work properly. The high flow velocity shock of the channel fluid causes additional vibration of the cantilever of the vortex generating body, which reduces the measurement accuracy. The impact of the large diameter is more obvious.
(4) Poor adaptability to the measurement of dirty media. The generator of the vortex flowmeter is easily smeared by the medium or entangled with dirt, which changes the size of the geometry and greatly affects the measurement accuracy.
(5) The requirements for straight pipe sections are high. Experts pointed out that the straight pipe section of the vortex flowmeter must ensure 20D after the first 40D to meet the measurement requirements.
(6) Poor temperature resistance. Vortex flowmeters generally only measure fluid flow in media below 300 °C.
USF entered industrial applications in the late 1960s, and has accounted for 4% to 6% of the sales of flow meters in various countries since the late 1980s. In 1992, the world's estimated sales volume was 3.548 million units, and domestic products were estimated to be 8,000-9000 units in the same period.
8 electromagnetic flowmeter (EMF)
The electromagnetic flowmeter is a meter for measuring conductive liquids according to Faraday's law of electromagnetic induction.
The electromagnetic flowmeter has a series of excellent characteristics, which can solve the problems that other flowmeters are not easy to apply, such as the measurement of dirty flow and corrosion flow.
In the 1970s and 1980s, electromagnetic flow had a major breakthrough in technology, making it a widely used type of flowmeter, and its percentage of usage in flow meters continued to rise.
advantage:
(1) The measuring channel is a smooth straight pipe with no obstruction. It is suitable for measuring liquid-solid two-phase fluids containing solid particles, such as pulp, mud, sewage, etc.
(2) The pressure loss caused by the flow detection is not generated, and the energy saving effect is good;
(3) The measured volumetric flow is virtually unaffected by changes in fluid density, viscosity, temperature, pressure, and conductivity;
(4) The flow range is large and the aperture range is wide;
(5) Corrosive fluids can be applied.
Disadvantages:
(1) The application of electromagnetic flowmeter has certain limitations. It can only measure the liquid flow of conductive medium, and can not measure the flow of non-conductive medium, such as gas and water for better heat treatment. In addition, the lining needs to be considered under high temperature conditions.
(2) The electromagnetic flowmeter determines the volume flow rate in the working state by measuring the speed of the conductive liquid. According to the measurement requirements, for liquid media, mass flow should be measured. The flow rate of the medium should be related to the density of the fluid. Different fluid media have different densities and vary with temperature. If the electromagnetic flowmeter converter does not consider the fluid density, it is not appropriate to give only the volume flow at normal temperature.
(3) The installation and commissioning of the electromagnetic flowmeter is more complicated than other flowmeters, and the requirements are more stringent. The transmitter and converter must be used together and cannot be used with two different types of instruments. When installing the transmitter, the selection from the installation site to the specific installation and commissioning must be carried out in strict accordance with the product specifications. The installation site must be free from vibration and strong magnetic fields. The transmitter and piping must be in good contact and well grounded during installation. The potential of the transmitter is equipotential to the fluid being measured. When using, the gas remaining in the measuring tube must be drained, otherwise it will cause a large measurement error.
(4) When the electromagnetic flowmeter is used to measure the viscous liquid with dirt, the sticky substance or sediment adheres to the inner wall or the electrode of the measuring tube, so that the output potential of the transmitter changes, which brings measurement error, and the dirt on the electrode reaches a certain level. Thickness may cause the meter to be unmeasured.
(5) The scaling or wear of the water supply pipe changes the inner diameter size, which will affect the original flow value and cause measurement error. If the inner diameter of the 100mm diameter meter changes by 1mm, it will bring about 2% additional error.
(6) The measurement signal of the transmitter is a small millivolt potential signal. In addition to the flow signal, it also contains some signals that are independent of the flow, such as phase voltage, quadrature voltage and common mode voltage. In order to accurately measure the flow rate, various interference signals must be eliminated to effectively amplify the flow signal. The performance of the flow converter should be improved. It is best to use a microprocessor type converter to control the excitation voltage. The excitation mode and frequency can be selected according to the nature of the fluid to be tested, and the in-phase interference and quadrature interference can be eliminated. However, the improved instrument structure is complicated and the cost is high.
(7) Higher price
Application overview:
Electromagnetic flowmeters are widely used in applications. Large-diameter instruments are mostly 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, chemical industry Strong corrosive liquid, pulp of non-ferrous metallurgical industry; small caliber, small caliber is often used in medical industry, food industry, biochemistry and other places with hygienic requirements. Since the EMF entered industrial application in the early 1950s, the field of use has expanded. Since the late 1980s, it has accounted for 16% to 20% of the sales volume of flow meters in various countries. China has developed rapidly in recent years. In 1994, sales were estimated at 6500-7500 units. The domestic ENF has a maximum diameter of 2~6m, and has the capability of real-flow calibration with a diameter of 3m.
9 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. Although the ultrasonic flowmeter appeared only in the 1970s, it is very popular because it can be made into a non-contact type and can be used for the measurement of the opening flow in conjunction with the ultrasonic water level gauge without disturbing or resisting the fluid.
Ultrasonic flowmeter can be divided into time difference type and Doppler type according to the measurement principle.
The time difference type ultrasonic flowmeter manufactured by the time difference principle has been widely concerned and used in recent years, and is an ultrasonic flowmeter which is most used by enterprises and enterprises at present.
Ultrasonic Doppler flowmeters fabricated by Doppler effect are often used to measure the medium with certain suspended particles or bubble media. The use of certain limitations, but solves the problem that the time difference ultrasonic flowmeter can only measure a single clear fluid. It is also considered to be the ideal instrument for non-contact measurement of two-phase flow.
advantage:
(1) Ultrasonic flowmeter is a non-contact measuring instrument that can be used to measure fluid flow and large pipe flow that are not easily accessible and difficult to observe. It does not change the flow of the fluid, does not create pressure loss, and is easy to install.
(2) It is possible to measure the flow rate of highly corrosive media and non-conductive media.
(3) The measuring range of the ultrasonic flowmeter is large, and the diameter of the pipe is from 20mm to 5m.
(4) Ultrasonic flowmeters can measure a variety of liquid and sewage flows.
(5) The volumetric flow measured by the ultrasonic flowmeter is not affected by the thermal property parameters such as temperature, pressure, viscosity and density of the fluid to be measured. Can be made in both fixed and portable form.
Disadvantages:
(1) The temperature measurement range of the ultrasonic flowmeter is not high, and generally only fluids with a temperature lower than 200 °C can be measured.
(2) Poor anti-interference ability. It is susceptible to ultrasonic noise interference caused by bubbles, scales, pumps and other sound sources, affecting measurement accuracy.
(3) Straight pipe sections are strictly required, for the first 20D and the last 5D. Otherwise, the dispersion is poor and the measurement accuracy is low.
(4) Uncertainty in installation will cause large errors in flow measurement.
(5) Measuring pipeline due to scaling, will seriously affect the measurement accuracy, bring significant measurement error, even in the case of serious no flow display
(6) Reliability and accuracy are not high (generally about 1.5 to 2.5), and the repeatability is poor.
(7) Short service life (the general accuracy can only be guaranteed for one year).
(8) Ultrasonic flowmeter determines the volume flow by measuring the fluid velocity. The mass flow rate should be measured for the liquid. The mass flow measured by the meter is obtained by multiplying the volume flow by the artificially set density. When the fluid temperature changes, The fluid density is variable, and the density value is artificially set, and the accuracy of the mass flow cannot be guaranteed. The fluid density can only be measured while measuring the fluid velocity, in order to obtain the true mass flow value through calculation.
Application overview:
The propagation time method is applied to clean, single-phase liquids and gases. Typical applications include factory effluent, blame, liquefied natural gas, etc.; gas applications have been well used in high pressure natural gas;
The Doppler method is suitable for two-phase fluids with a low heterogeneous content, such as untreated sewage, factory effluent, dirty process fluids; usually not suitable for very clean liquids.
10 mass flow meter
Since the volume of the fluid is affected by parameters such as temperature and pressure, it is necessary to give the parameters of the medium when the flow rate is expressed by the volume flow. In the case of changing media parameters, it is often difficult to achieve this requirement, resulting in distortion of the meter display value. Therefore, mass flow meters have been widely used and valued. Mass flow meters are available in both direct and indirect versions. Direct mass flow meters are measured using principles directly related to mass flow. Currently used mass flow meters such as calorimetric, angular momentum, vibratory gyro, Magnus effect and Coriolis force. The indirect mass flow meter is obtained by directly multiplying the density meter by the volumetric flow rate to obtain the mass flow rate.
In modern industrial production, the operating parameters such as temperature and pressure of the flowing working fluid are continuously improved. In the case of high temperature and high pressure, due to the material and structure, the application of the direct mass flowmeter is difficult, and the indirect quality is encountered. Flowmeters are often not suitable for practical applications because they are limited by the range of humidity and pressure. Therefore, a temperature-pressure-compensated mass flowmeter is widely used in industrial production. It can be regarded as an indirect mass flow meter. Instead of using a density meter, it uses the relationship between temperature, pressure and density. It uses the temperature and pressure signals to calculate the density signal by function, and multiplies it by the volume flow. Mass Flow. At present, temperature and pressure-compensated mass flowmeters have been put into practical use. However, when the measured medium parameters vary widely or rapidly, it will be difficult or impossible to correctly compensate, so further study the mass flow rate applicable in actual production. Meters and densitometers are still a topic.
11 thermal mass flow meter (constant temperature difference TMF)
advantage:
(1) Ball valve installation, easy to install and disassemble. It can be installed with pressure.
(2) Direct measurement of mass flow based on King's law. The measured values ​​are not affected by pressure and temperature.
(3) The response is rapid.
(4) The range of the measuring range is large, the minimum installation of the pipeline can measure the flow of the 8.8mm pipeline, and the maximum can be measured 30''
(5) Plug-in type flow meter, one flow meter can be used to measure a variety of pipe diameters.
Disadvantages:
(1) Accuracy is less than other types of flowmeters, generally 3%.
(2) The scope of application is narrow and can only be used to measure dry non-explosive gases such as compressed air, nitrogen, argon and other neutral gases.
12 Coriolis mass flow meter (CMF)
The Coriolis mass flow meter (hereinafter referred to as CMF) is a direct mass flow meter made by the Coriolis force principle which is proportional to the mass flow when the fluid flows through the vibrating tube.
The application of CMF in China started late. In recent years, several manufacturing plants (such as Taihang Instrument Factory) have developed and supplied the market by themselves; there are also several manufacturing plants that form joint ventures or use foreign technology to produce series instruments.
Foreign CMF has developed more than 30 series. The technical focus of each series development is: design innovation on the structure of flow detection and measuring tube; improving the stability and accuracy of the zero point of the instrument; increasing the deflection of the measuring tube, improving the sensitivity; improving the stress of the measuring tube Distribution, reduce fatigue damage, and enhance the ability to resist vibration.
13 open channel flowmeter
Unlike the previous ones, it is a flow meter that measures the free flow of a free surface in a non-full tubular open channel.
A waterway that is not full of tubular flow is called an open channel, and an open channel flowmeter that measures the flow of water in an open channel is called an open channel flowmeter.
In addition to the circular shape, the open channel flowmeter has various shapes such as U-shape, trapezoidal shape, and rectangular shape.
All urban water supply diversion canals for open channel flowmeter applications; diversion and drainage channels for thermal power plants, sewage treatment inflows and discharge channels; water discharge for industrial and mining enterprises; and channels for water conservancy projects and agricultural irrigation. It is estimated that 1995 units account for 1.6% of the total flow meters, but there is no estimated data for domestic applications.
14 electrostatic flowmeter (electrostatic flowmeter)
The Tokyo Institute of Technology in Japan developed an electrostatic flowmeter suitable for the measurement of low conductivity liquid flow in petroleum pipelines.
The metal measuring tube of the electrostatic flowmeter is connected to the pipe system insulatively, and the electric charge in the measuring tube can be known by measuring the static charge on the capacitor. They performed real-flow tests on metal and plastic measuring tube instruments with inner diameters of 4~8mm copper and stainless steel. The tests showed that the flow rate and charge were close to linear.
15 combined effects meter (combined effects meter)
The working principle of the meter is based on the deformation of the fluid induced by the momentum and pressure of the fluid, and the deformation of the composite effect is measured to obtain the flow. This instrument was developed by the GMI Engineering and Management Institute of the United States and has applied for two patents.
16 tachmetric flowrate sensor
It was developed by the Russian Scientific Engineering Center Industrial Instrument Company and was developed based on the theory of suspension effects. The instrument has been successfully applied in several sites (for example, installing more than 2,000 hot water flows in nuclear power plants for 8 consecutive years) and is still improving to expand the application area.
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