Understand the working principles, advantages, and disadvantages of various flow meters in one article!

The instruments used to measure fluid flow are collectively referred to as flow meters or flow meters. Flow meter is one of the important instruments in industrial measurement. With the development of industrial production, the requirements for accuracy and range of flow measurement are becoming increasingly high. Flow measurement technology is advancing rapidly, and in order to adapt to various applications, various types of flow meters have emerged one after another. Currently, more than 100 types of flow meters have been put into use.
Flowmeter
Each product has its specific applicability and limitations. According to measurement principles, it can be divided into mechanical principles, thermal principles, acoustic principles, electrical principles, optical principles, atomic physics principles, etc.
According to the structural principle of flow meters, there are volumetric flow meters, differential pressure flow meters, float flow meters, turbine flow meters, electromagnetic flow meters, vortex flow meters in fluid oscillation flow meters, mass flow meters, and insertion flow meters.
According to the measurement object, there are two main categories: closed pipelines and open channels; According to the measurement purpose, it can be divided into total measurement and flow measurement, and their instruments are called total meter and flow meter respectively. A total flow meter measures the flow rate through a pipeline over a period of time, expressed as the quotient of the total amount flowing over a short period of time divided by that time. In fact, flow meters are usually equipped with cumulative flow devices for use as total flow meters, and total flow meters are also equipped with flow signaling devices. Therefore, strictly distinguishing between flow meters and total meters has no practical significance.
1. Classified by measurement principle
1. Mechanics principle: Instruments belonging to this type of principle include differential pressure and rotor type instruments that utilize Bernoulli's theorem; The impulse equation and movable tube equation using the momentum theorem; Using the direct mass formula of Newton's second law; Target based on the principle of fluid momentum; Turbine type using the angular momentum theorem; Vortex type and vortex street type utilizing the principle of fluid oscillation; Utilize pitot tube type, volumetric type, weir, trough type, etc. that utilize the total static pressure difference.
2. Electrical principles: Instruments used for this type of principle include electromagnetic, differential capacitive, inductive, strain resistance, etc.
3. Acoustic principles: There are ultrasonic and acoustic (shock wave) methods that use acoustic principles for flow measurement.
4. Thermal principles: There are various methods for measuring flow rate using thermal principles, such as calorimetry, direct calorimetry, indirect calorimetry, etc.
5. Optical principles: Laser, photoelectric, and other instruments belong to this type of principle.
6. Atomic physics principles: Nuclear magnetic resonance, nuclear radiation, and other instruments belong to this type of principle.
7. Other principles: including labeling principles (tracing principles, nuclear magnetic resonance principles), related principles, etc.
2. Classified by the principle of flow meter structure
Based on the actual situation of current flowmeter products and the structural principle of flowmeters, they can be roughly classified into the following types:
1. Differential pressure flowmeter
Differential pressure flowmeter is an instrument that calculates flow based on the differential pressure generated by the flow detection component installed in the pipeline, known fluid conditions, and the geometric dimensions of the detection component and the pipeline.
The differential pressure flowmeter consists of a primary device (detection component) and a secondary device (differential pressure conversion and flow display instrument). Differential pressure flow meters are usually classified in the form of detection components, such as orifice flow meters, Venturi flow meters, and averaging tube flow meters.
The secondary device includes various mechanical, electronic, and electromechanical integrated differential pressure gauges, differential pressure transmitters, and flow display instruments. It has developed into a large category of instruments with a high degree of standardization (serialization, generalization, and normalization) and a wide range of types and specifications. It can measure both flow parameters and other parameters (such as pressure, level, density, etc.).
The detection components of differential pressure flow meters can be divided into several categories according to their operating principles: throttling device, hydraulic resistance type, centrifugal type, dynamic pressure head type, dynamic pressure head gain type, and jet type.
Testing items can be divided into two categories based on their standardization level: standard and non-standard.
The so-called standard test piece is designed, manufactured, installed, and used according to standard documents, without the need for actual flow calibration to determine its flow value and estimate measurement errors.
Non standard testing components are those with poor maturity and have not yet been included in international standards.
Differential pressure flowmeter is the most widely used type of flowmeter, with its usage ranking first among various flow meters. In recent years, due to the emergence of various new types of flow meters, their usage percentage has gradually decreased, but they are still the most important type of flow meter at present.
advantage:
(1) The most widely used orifice plate flowmeter has a sturdy structure, stable and reliable performance, and a long service life;
(2) It has a wide range of applications and there is currently no type of flow meter that can be compared to it;
(3) The detection components, transmitters, and display instruments are produced by different manufacturers, facilitating economies of scale production.
Disadvantages:
(1) The measurement accuracy is generally low;
(2) Narrow range, generally only 3:1~4:1;
(3) High requirements for on-site installation conditions;
(4) High pressure loss (referring to orifice plates, nozzles, etc.).
Application Overview:
Differential pressure flowmeter has a wide range of applications, including flow measurement in closed pipelines for various objects such as fluids: single-phase, mixed phase, clean, dirty, viscous flow, etc; In terms of working conditions: normal pressure, high pressure, vacuum, normal temperature, high temperature, low temperature, etc; In terms of pipe diameter: from a few millimeters to a few meters; In terms of flow conditions: subsonic, sonic, pulsating flow, etc. It accounts for approximately 1/4 to 1/3 of the total usage of flow meters in various industrial sectors.
2. Orifice flowmeter
advantage:
Standard throttling components are widely used worldwide and have been recognized by international standard organizations. They can be put into use without the need for actual flow calibration and are the only instrument in flow meters that is easy to replicate in structure. They are simple, sturdy, stable and reliable in performance, and cost-effective;
Widely applicable, including all single-phase fluids (liquid, gas, steam) and some mixed phase flows, with products available for pipe diameters and working conditions (temperature, pressure) in general production processes.
The detection components and differential pressure display instruments can be produced separately by different manufacturers, facilitating specialized scale production;
Disadvantages:
The repeatability and accuracy of measurements are at a moderate level in flow meters, but due to the complex influence of numerous factors, it is difficult to improve accuracy.
The range is narrow, and due to the correlation between flow coefficient and Reynolds number, the general range is only 3:1 to 4:1. There are long requirements for the length of straight pipe sections, which are generally difficult to meet. Especially for larger pipe diameters, the problem becomes more prominent;
The pressure loss is large, and usually in order to maintain the normal operation of an orifice flowmeter, the water pump needs additional power to overcome the pressure loss of the orifice plate. The additional power consumption can be directly determined by pressure loss and flow calculation, which requires an additional tens of thousands of kilowatt hours of electricity consumption per year, equivalent to tens of thousands of yuan.
The sharp angle line inside the orifice plate is used to ensure accuracy, so it is sensitive to corrosion, wear, scaling, and dirt. Long term use makes it difficult to guarantee accuracy, and it needs to be disassembled and inspected once a year. Using flange connections can easily lead to issues such as running, emitting, dripping, and leaking, greatly increasing maintenance workload.
3. Float flowmeter
Float flowmeter, also known as rotor flowmeter, is a type of variable area flowmeter. In a vertical conical tube that expands from bottom to top, the gravity of the circular cross-section float is supported by liquid dynamics, allowing the float to freely rise and fall inside the conical tube.
Float flowmeter is the most widely used type of flowmeter, second only to differential pressure flowmeter, and plays a crucial role in small and micro flow.
In the mid-1980s, sales in Japan, Western Europe, and the United States accounted for 15% to 20% of flow meters. The estimated production in China in 1990 was between 120000 and 140000 units, of which over 95% were glass cone tube float flowmeters.
characteristic:
(1) The glass cone tube float flowmeter has a simple structure and is easy to use, but its disadvantage is low pressure resistance and a high risk of glass tube fragility; 
(2) Suitable for small diameters and low flow rates;
(3) Low pressure loss.
4. Volumetric flowmeter
Positive displacement flowmeter, also known as fixed displacement flowmeter, abbreviated as PD flowmeter, is the most accurate type of flow meter. It uses mechanical measuring elements to continuously divide the fluid into individual known volume parts, and measures the total volume of the fluid based on the number of times the measuring chamber repeatedly fills and discharges that volume part of the fluid.
Volumetric flow meters can be classified according to their measuring components, including elliptical gear flow meters, scraper flow meters, dual rotor flow meters, rotary piston flow meters, reciprocating piston flow meters, disc flow meters, liquid sealed rotary cylinder flow meters, wet gas meters, and membrane gas meters.
advantage:
(1) High measurement accuracy;
(2) The installation of pipeline conditions does not affect the measurement accuracy;
(3) Can be used for measuring high viscosity liquids;
(4) Wide range;
(5) Direct reading instruments do not require external energy sources and can directly accumulate data. The total amount is clear and easy to operate.
Disadvantages:
(1) The results are complex and bulky;
(2) There are significant limitations in the type, diameter, and working state of the tested medium;
(3) Not suitable for high and low temperature environments;
(4) Most instruments are only suitable for clean single-phase fluids;
(5) Generate noise and vibration.
Application Overview:
Volumetric flow meters, differential pressure flow meters, and float flow meters are among the three most widely used types of flow meters, commonly used for measuring the total amount of expensive media such as oil and natural gas.
In recent years, the sales amount of PD flow meters (excluding household gas meters and household water meters) in industrialized countries has accounted for 13% to 23% of flow meters; China accounts for about 20%, with an estimated production of 340000 units in 1990 (excluding household gas meters), of which elliptical gear type and waist wheel type account for about 70% and 20% respectively.
5. Types of sewage flow meters
Sewage flow meters are classified according to their measurement principles:
1. Flow meters include throttling flow meters, pitot tube flow meters, averaging tube flow meters, rotor flow meters, and target flow meters. These flow meters use the Bernoulli equation principle to reflect flow by measuring fluid differential pressure signals;
2. Flow meters include turbine flow meters, vortex street flow meters, electromagnetic flow meters, Doppler ultrasonic flow meters, and hot wire speed measurement flow meters, which reflect flow rate by measuring fluid flow velocity;
3. Flow meters include gear flow meters, scraper flow meters, and rotary piston flow meters, which reflect flow rates by measuring small volumes of standard volumes;
4. Flow meters include thermal mass flow meters, differential pressure mass flow meters, impeller mass flow meters, Coriolis mass flow meters, and indirect mass flow meters, which reflect flow by measuring fluid mass;
5. The flow meter has a weir type flow meter, which reflects the flow rate by measuring the liquid level.
Characteristics of sewage flowmeter:
1. The sewage flowmeter has a simple structure, is sturdy and reliable, and has a long service life.
2. There are no moving parts or resistance parts inside the measuring tube, no pressure loss, no blockage, reliable measurement, strong anti-interference ability, small size, light weight, easy installation, low maintenance, and wide measurement range; The measurement is not affected by changes in fluid temperature, density, pressure, viscosity, conductivity, etc. It can be retrofitted and installed by drilling holes on old pipelines, with simple construction and installation and small engineering quantities.
6. Turbine flowmeter
Turbine flowmeter is the main type of velocity flowmeter, which uses a multi blade rotor (turbine) to sense the average flow velocity of the fluid and derive the flow rate or total amount from it.
Generally, it consists of two parts: sensors and displays, or it can be made as a whole.
Turbine flow meters, volumetric flow meters, and Coriolis mass flow meters are known as the three types of flow meters with the best repeatability and accuracy. As one of the top ten types of flow meters, their products have developed into a large-scale production of multiple varieties and series.
advantage:
(1) High precision, among all flow meters, it belongs to the most accurate flow meter;
(2) Good repeatability;
(3) Yuan zero drift, good anti-interference ability;
(4) Wide range;
(5) Compact structure.
Disadvantages:
(1) Unable to maintain calibration characteristics for a long time;
(2) Fluid properties have a significant impact on flow characteristics.
Application Overview:
Turbine flow meters are widely used in measuring objects such as petroleum, organic liquids, inorganic liquids, liquefied gases, natural gas, and low-temperature flows.
Turbine flowmeter is a natural measuring instrument second only to orifice flowmeter in terms of usage. In the Netherlands alone, more than 2600 gas turbine flowmeters of various sizes and pressures ranging from 0.8 to 6.5 MPa are used in natural gas pipelines, making them excellent natural gas measuring instruments.
7. Vortex flowmeter (USF)
picture
A vortex flowmeter is an instrument that places a non streamlined vortex generator in a fluid, and the fluid alternately separates and releases two series of regularly arranged vortices on both sides of the generator. When the flow cross-section is constant, the flow velocity is proportional to the volumetric flow rate. Therefore, measuring the oscillation frequency can determine the flow rate. Vortex flowmeters can be classified according to frequency detection methods, such as stress type, strain type, capacitance type, thermal sensitive type, vibration type, photoelectric type, and ultrasonic type. This type of flowmeter was developed and evolved in the 1970s, and due to its advantages of having no rotating parts and pulse digital output, it has great potential for development.
advantage
(1) Vortex flowmeter has no movable parts, simple measuring element structure, reliable performance, and long service life.
(2) The vortex flowmeter has a wide measurement range. The range ratio can generally reach 1:10.
(3) The volumetric flow rate of a vortex flowmeter is not affected by thermal parameters such as temperature, pressure, density, or viscosity of the fluid being measured. Generally, there is no need for separate calibration. It can measure the flow rate of liquids, gases, or vapors.
(4) It causes minimal pressure loss.
(5) High accuracy, repeatability of 0.5%, and low maintenance.
shortcoming
(1) The volumetric flow rate of a vortex flowmeter during operation is not affected by thermal parameters such as temperature, pressure, and density of the fluid being measured. However, the final measurement result for liquids or vapors should be mass flow rate, and for gases, the final measurement result should be standard volumetric flow rate. Both mass flow rate and standard volume flow rate must be converted based on fluid density, taking into account changes in fluid density caused by variations in fluid operating conditions.
(2) The main factors causing flow measurement errors are: measurement errors caused by uneven flow velocity in pipelines; Unable to accurately determine the medium density when fluid conditions change; Assuming wet saturated steam as dry saturated steam for measurement. If these errors are not limited or eliminated, the total measurement error of the vortex flowmeter will be significant.
(3) Poor anti vibration performance. External vibrations can cause measurement errors in vortex flowmeters, and even prevent them from functioning properly. The high flow velocity impact of the channel fluid will cause additional vibrations in the cantilever of the vortex generator, resulting in a decrease in measurement accuracy. The impact of larger pipe diameters is more pronounced.
(4) Poor adaptability to measuring dirty media. The generating body of vortex flowmeter is easily contaminated by the medium or entangled by dirt, which changes the geometric dimensions and greatly affects the measurement accuracy.
(5) The straight pipe section requires high standards. Experts point out that the straight section of the vortex flowmeter must ensure the first 40D and the last 20D to meet the measurement requirements.
(6) Poor temperature resistance. Vortex flow meters can generally only measure fluid flow rates of media below 300 ℃.
USF entered industrial applications in the late 1960s and has accounted for 4% to 6% of the sales revenue of flow meters in various countries since the late 1980s. In 1992, the estimated global sales volume was 354800 units, while the estimated domestic products during the same period were between 8000 and 9000 units.
8. Electromagnetic flowmeter (EMF)
Electromagnetic flowmeter is an instrument made according to Faraday's law of electromagnetic induction for measuring conductive liquids.
Electromagnetic flow meters have a series of excellent characteristics that can solve problems that are not easily applicable to other flow meters, such as measuring dirty and corrosive flows.
In the 1970s and 1980s, there were significant technological breakthroughs in electromagnetic flow, making it a widely used type of flow meter, and its usage percentage in flow meters continued to rise.
advantage:
(1) The measuring channel is a smooth straight pipe that will not block, suitable for measuring liquid-solid two-phase fluids containing solid particles, such as pulp, mud, sewage, etc;
(2) No pressure loss caused by flow detection, good energy-saving effect;
(3) The measured volumetric flow rate is actually not significantly affected by changes in fluid density, viscosity, temperature, pressure, and conductivity;
(4) Large flow range and wide aperture range;
(5) Can be used with corrosive fluids.
Disadvantages:
(1) The application of electromagnetic flowmeter has certain limitations. It can only measure the liquid flow rate of conductive media and cannot measure the flow rate of non-conductive media, such as gas and water treatment for heating water. In addition, its lining needs to be considered under high temperature conditions.
(2) Electromagnetic flowmeter determines the volumetric flow rate under working conditions by measuring the velocity of conductive liquid. According to the measurement requirements, for liquid media, the mass flow rate should be measured, and the measurement of medium flow rate should involve the density of the fluid. Different fluid media have different densities and vary with temperature. If the electromagnetic flowmeter converter does not consider fluid density and only provides volumetric flow rate at room temperature, it is not appropriate.
(3) The installation and debugging of electromagnetic flow meters are more complex and require stricter requirements than other flow meters. The transmitter and converter must be used together, and two different types of instruments cannot be used between them. When installing the transmitter, it is necessary to strictly follow the requirements of the product manual from the selection of the installation location to the specific installation and debugging. The installation location should not have vibration or strong magnetic fields. During installation, it is necessary to ensure good contact and grounding between the transmitter and the pipeline. The potential of the transmitter is equal to the potential of the measured fluid. When using, it is necessary to exhaust the gas remaining in the measuring tube, otherwise it will cause significant measurement errors.
(4) When an electromagnetic flowmeter is used to measure viscous liquids with dirt, viscous substances or sediment adhere to the inner wall of the measuring tube or electrode, causing a change in the output potential of the transmitter and resulting in measurement errors. When the dirt on the electrode reaches a certain thickness, it may cause the instrument to be unable to measure.
(5) The scaling or wear of the water supply pipeline will change the inner diameter size, which will affect the original flow value and cause measurement errors. If the inner diameter of a 100mm diameter instrument changes by 1mm, it will result in an additional error of about 2%.
(6) The measurement signal of the transmitter is a very small millivolt level potential signal, which contains not only flow signals but also some signals unrelated to flow, such as phase voltage, orthogonal voltage, and common mode voltage. In order to accurately measure flow, it is necessary to eliminate various interference signals and effectively amplify the flow signal. The performance of the flow converter should be improved, preferably using a microprocessor based converter to control the excitation voltage. The excitation mode and frequency should be selected according to the properties of the measured fluid to eliminate in-phase and quadrature interference. But the improved instrument structure is complex and costly.
(7) The price is relatively high.
Application Overview:
Electromagnetic flow meters have a wide range of applications, with large-diameter instruments being commonly used in water supply and drainage engineering; Small and medium-sized calibers are commonly used in high demand or difficult to measure applications, such as cooling water control for blast furnace tuyere in the steel industry, measurement of pulp and black liquor in the paper industry, strong corrosive liquids in the chemical industry, and slurry in the non-ferrous metallurgy industry; Small caliber and micro caliber are commonly used in places with hygiene requirements such as the pharmaceutical industry, food industry, and biochemistry. Since EMF entered industrial applications in the early 1950s, its usage areas have been expanding day by day. Since the late 1980s, it has accounted for 16% to 20% of the sales revenue of flow meters in various countries.
China has developed rapidly in recent years, with an estimated sales of 6500-7500 units in 1994. ENF with a maximum diameter of 2-6m has been produced domestically, and it has the equipment capability to verify the diameter of 3m in real flow.
9. Ultrasonic flowmeter
Ultrasonic flowmeter is designed based on the principle that the speed of ultrasonic propagation in a flowing medium is equal to the geometric sum of the average flow velocity of the measured medium and the speed of the sound wave itself. It also reflects the flow rate by measuring the flow velocity. Although ultrasonic flow meters only appeared in the 1970s, they are very popular because they can be made into non-contact types and can be linked with ultrasonic water level gauges for open flow measurement, without causing disturbance or resistance to the fluid.
Ultrasonic flow meters can be divided into time difference and Doppler based on their measurement principles.
The time difference ultrasonic flowmeter manufactured using the time difference principle has received widespread attention and use in recent years, and is currently the most commonly used ultrasonic flowmeter in enterprises and institutions.
Ultrasonic Doppler flow meters manufactured using the Doppler effect are often used to measure media with certain suspended particles or bubbles, which have certain limitations in use. However, they solve the problem that time difference ultrasonic flow meters can only measure a single clear fluid and are also considered ideal instruments 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 rates and large pipe diameters that are difficult to contact and observe. It will not change the flow state of the fluid, will not cause pressure loss, and is easy to install.
(2) It can measure the flow rate of highly corrosive and non-conductive media.
(3) The measurement range of ultrasonic flowmeter is large, with pipe diameters ranging from 20mm to 5m
(4) Ultrasonic flow meters can measure the flow rates of various liquids and wastewater.
(5) The volumetric flow rate measured by an ultrasonic flowmeter is not affected by thermal properties such as temperature, pressure, viscosity, and density of the fluid being measured. It can be made in two forms: fixed and portable.
Disadvantages:
(1) The temperature measurement range of ultrasonic flow meters is not high, generally only capable of measuring fluids with temperatures below 200 ℃.
(2) Poor anti-interference ability. Easy to be affected by ultrasonic noise interference from bubbles, scaling, pumps, and other sources, which can affect measurement accuracy.
(3) The straight pipe section has strict requirements, with the first 20D and the last 5D. Otherwise, the discreteness is poor and the measurement accuracy is low.
(4) The uncertainty of installation can cause significant errors in flow measurement.
(5) The scaling of measuring pipelines can seriously affect measurement accuracy, resulting in significant measurement errors, and even in severe cases, the instrument may not display flow.
(6) The reliability and accuracy level are not high (generally around 1.5-2.5 levels), and the repeatability is poor.
(7) Short service life (generally, accuracy can only be guaranteed for one year).
(8) Ultrasonic flowmeter determines the volumetric flow rate by measuring the fluid velocity. For liquids, the mass flow rate should be measured. The instrument measures the mass flow rate by multiplying the volumetric flow rate by a manually set density. When the fluid temperature changes, the fluid density changes. The manually set density value cannot guarantee the accuracy of the mass flow rate. Only by measuring both fluid velocity and fluid density can the true mass flow rate value be obtained through calculation.
Application Overview:
The propagation time method is applied to clean, single-phase liquids and gases. Typical applications include factory discharge liquids, strange liquids, liquefied natural gas, etc; There is already good experience in the application of gas in the field of high-pressure natural gas;
The Doppler method is suitable for two-phase fluids with relatively low heterogeneous content, such as untreated wastewater, factory discharge fluids, and dirty process fluids, and is usually not suitable for very clean liquids.
10. Mass flow meter
Due to the influence of temperature, pressure, and other parameters on the volume of a fluid, it is necessary to provide the parameters of the medium when using volumetric flow rate to represent the flow rate. In the case of constantly changing medium parameters, it is often difficult to meet this requirement, resulting in distortion of instrument display values.
Therefore, mass flow meters have been widely used and valued. There are two types of quality flow scoring: direct and indirect. Direct mass flow meters use principles directly related to mass flow for measurement. Currently, commonly used mass flow meters include calorimetry, angular momentum, vibration gyroscope, Magnus effect, and Coriolis force. The indirect mass flow meter calculates the mass flow rate by directly multiplying the density meter with the volumetric flow rate.
In modern industrial production, the operating parameters such as temperature and pressure of the flowing working fluid are constantly increasing. Under high temperature and pressure conditions, due to material and structural reasons, the application of direct mass flow meters encounters difficulties, while indirect mass flow meters are often difficult to apply in practice due to the limitations of humidity and pressure range of density meters.
Therefore, temperature pressure compensation mass flow meters are widely used in industrial production. It can be regarded as an indirect mass flow meter, not equipped with a density meter, but using the relationship between temperature, pressure, and density. The temperature and pressure signals are converted into density signals through functional operations, and the mass flow rate is obtained by multiplying them with the volumetric flow rate. At present, although temperature and pressure compensated mass flow meters have been put into practical use, it will be difficult or impossible to compensate correctly when the parameters of the measured medium change widely or rapidly. Therefore, further research on mass flow meters and density meters applicable in practical production is still a topic.
11. Thermal mass flowmeter (constant temperature difference TMF)
advantage:
(1) Ball valve installation, easy to install and disassemble. And it can be installed under pressure.
(2) Based on King's Law, directly measure mass flow rate. The measured value is not affected by pressure and temperature.
(3) Respond quickly.
(4) The range is large, and the pipeline installation can measure the flow rate of a minimum 8.8mm pipeline and a maximum of 30.
(5) Plug in type flow meter, one flow meter can be used to measure multiple pipe diameters.
Disadvantages:
(1) The accuracy is inferior to other types of flow meters, generally at 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 flowmeter (CMF) utilizes fluid flow in a vibrating tube. A direct mass flow meter based on the principle of Coriolis force that is proportional to the mass flow rate.
The application of CMF in China started relatively late, and in recent years, several manufacturing plants (such as Taihang Instrument Factory) have independently developed and supplied the market; Several manufacturing plants have formed joint ventures or adopted foreign technology to produce a series of instruments.
More than 30 series of CMF have been developed abroad, with a focus on technological innovation in the design of flow detection and measurement tube structures; Improve the stability and accuracy of instrument zero points; Increase the deflection of the measuring tube to improve sensitivity; Improve the stress distribution of the measuring tube, reduce fatigue damage, and enhance the ability to resist vibration interference.
13. Open channel flowmeter
Unlike the previous methods, it is a flow meter used to measure free surface natural flow in non full tubular open channels.
A waterway with non full pipe flow is called an open channel, and the one that measures the flow rate of water in the open channel is called an open channel flowmeter.
In addition to circular flow meters, open channel flow meters also come in various shapes such as U-shape, trapezoid, rectangle, etc.
The application of open channel flow meters in all urban water supply and diversion channels; Water diversion and drainage channels, sewage treatment inflow and discharge channels in thermal power plants; Water discharge from industrial and mining enterprises, as well as channels for water conservancy projects and agricultural irrigation.
14. Electrostatic flowmeter
(electrostatic flowmeter)
Tokyo Institute of Technology in Japan has developed an electrostatic flowmeter suitable for measuring the flow rate of low conductivity liquids in oil pipelines.
The metal measuring tube of the electrostatic flowmeter is insulated and connected to the piping system. By measuring the static charge on the capacitor, the charge inside the measuring tube can be determined. They conducted real flow tests on metal and plastic measuring tube instruments with inner diameters of 4-8mm, including copper, stainless steel, etc. The tests showed that the relationship between flow rate and charge was close to linear.
15. Composite effect flow meter
(combined effects meter)
The working principle of this instrument is based on the deformation generated by the momentum and pressure of the fluid acting on the instrument chamber, measuring the deformation of the composite effect to obtain the flow rate. This instrument was developed by the GMI School of Engineering and Management in the United States and has applied for two patents.
16. Tachometer type flow sensor
(tachmetric flowrate sensor)
It was developed by the Industrial Instrumentation Company of the Russian Science and Engineering Center based on the theory of suspension effect. This instrument has been successfully applied in several fields (such as installing more than 2000 units to measure hot water flow in nuclear power plants and using it continuously for 8 years), and is still being improved to expand its application areas.