During this time, many seven friends left messages to Xiaoqi, wanting to see the content of the flow meter, so today Xiaoqi will share the knowledge of the flow meter with you again. The flowmeter is a commonly used measuring instrument, and the measurement accuracy, stability, and ease of use of the flowmeter have certain applications in many fields. There are many types of flow meters, and the functions and measurement ranges of each different flow meter are different. So how many specific flow meters are classified? What are the disadvantages and applications of each flow meter?

Classification of flow meters

Meters that measure fluid flow are collectively known 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 the accuracy and range of flow measurement are getting higher and higher, and the flow measurement technology is changing with each passing day. In order to adapt to various uses, various types of flow meters have been introduced. At present, more than 100 types of flow meters have been put into use.

Each product has its specific applicability and limitations. According to the measurement principle, it is divided into mechanical principle, thermal principle, acoustic principle, electrical principle, optical principle, atomic physics principle, etc.

Classification 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 plug-in flow meters.

According to the measurement object, there are two categories: closed pipelines and open channels; According to the measurement purpose, it can be divided into total measurement and flow measurement, and its instruments are called total meters and flow meters respectively. The total gauge measures the flow through the pipeline over a period of time, which is expressed as the total amount flowing in a short period of time divided by the quotient of that time. Therefore, it is no longer practical to divide the flow meter and the total scale in a strict sense.

1. Classification according to measurement principle

1. Mechanical principles: instruments belonging to this type of principle include differential pressure type and rotor type using Bernoulli's theorem; impulse type and movable tube type using momentum theorem; using the direct mass formula of Newton's second law; targets using the principle of fluid momentum; turbine type using the angular momentum theorem; vortex type and vortex street type using the principle of fluid oscillation; Pitot tube type using total static pressure difference, volumetric type, weir type, trough type, etc.

2. Electrical principle: The instruments used for this type of principle include electromagnetic type, differential capacitive type, inductive type, strain resistance type, etc.

3. Acoustic principle: The flow measurement using acoustic principle is ultrasonic. Acoustic type (shock wave type), etc.

4. Thermal principle: The thermal principle is used to measure the flow rate, such as caloric type, direct calorimetry type, indirect calorimetry type, etc.

5. Optical principle: laser, photoelectric type, etc. are instruments belonging to this type of principle.

6. Originally based on physical principles: nuclear magnetic resonance type, nuclear radiation type, etc. are instruments belonging to this kind of principle.

7. Other principles: there are marking principles (tracing principle, nuclear magnetic resonance principle), related principles, etc.

2. Classification according to the structural principle of the flowmeter

According to the actual situation of current flowmeter products, according to the structural principle of flowmeter, it can be roughly summarized into the following types:

1. Differential pressure flowmeter

The differential pressure flow meter is a meter that calculates the flow rate based on the differential pressure generated by the flow detector installed in the pipeline, the known fluid conditions and the geometric dimensions of the detection part and the pipeline.

The differential pressure flow meter consists of a primary device (detection part) and a secondary device (differential pressure conversion and flow display instrument). Differential pressure flow meters are usually classified in the form of test parts, such as orifice flow meters, venturi flow meters, average velocity flow meters, etc.

The secondary device is a variety of mechanical, electronic, mechatronic integrated differential pressure meters, differential pressure transmitters and flow display instruments. It has developed into a large class of instruments with a high degree of three modernizations (serialization, generalization and standardization) and a large number of types and specifications, which can measure both flow parameters and other parameters (such as pressure, level, density, etc.).

The detection parts of differential pressure flowmeters can be divided into several categories according to their working principles: throttling device, hydraulic resistance type, centrifugal type, dynamic indenter type, dynamic indenter gain type and jet type.

Tested parts can be divided into two categories according to their degree of standardization: standard and non-standard.

The so-called standard test parts are designed and manufactured, installed and used according to the standard documents, and their flow values and estimated measurement errors can be determined without real flow calibration.

Non-standard test parts are less mature and have not yet been included in international standards.

Differential pressure flow meters are one of the most widely used flow meters, and their usage ranks first among all types of flow meters. In recent years, due to the advent of various new flow meters, its usage percentage has gradually decreased, but it is still the most important type of flow meter.

Pros:

(1) The most used orifice type flowmeter has a solid structure, stable and reliable performance, and a long service life;

(2) The application range is wide, and there is no type of flow meter that can be compared with it;

(3) The test parts, transmitters, and display instruments are produced by different manufacturers, which is convenient for economies of scale.

Cons:

(1) The measurement accuracy is generally low;

(2) The range is narrow, generally only 3:1~4:1;

(3) High requirements for on-site installation conditions;

(4) Large pressure loss (referring to orifice plates, nozzles, etc.).

Application Overview:

The differential pressure flowmeter has a particularly wide range of applications, and is used in various objects in the flow measurement of closed pipelines, such as fluids: single-phase, miscible, clean, dirty, viscous flow, etc.; Working status: normal pressure, high pressure, vacuum, normal temperature, high temperature, low temperature, etc.; Pipe diameter: from a few mm to several m; In terms of flow conditions: subsonic speed, speed of sound, pulsating flow, etc. Its consumption in various industrial sectors accounts for about 1/4~1/3 of the total consumption of flow meters.

2-well plate flow meter

Pros:

Standard throttle parts are universally used and recognized by international standards organizations, and can be put into use without real-current calibration, and are the only ones in flow meters. The structure is easy to replicate, simple, firm, stable and reliable in performance, and low price;

Cons:

The repeatability and accuracy of measurements are at a moderate level among flow meters, and the accuracy is difficult to improve due to the intricacies of many factors. The range is narrow, because the flow coefficient is related to the Reynolds number, the general range is only 3∶1~4∶1. There are long straight pipe section length requirements, which are generally difficult to meet. Especially for larger pipe diameters, the problem is more prominent; large pressure loss; Normally, to maintain the normal operation of an orifice flow meter, the pump requires additional power to overcome the pressure loss of the orifice.

The orifice plate is made of the sharp angle of the inner hole to ensure accuracy, so it is sensitive to corrosion, wear, scaling, and dirt, and the accuracy of long-term use is difficult to guarantee, so it needs to be removed and compulsorily inspected once a year. The use of flange connection is easy to cause the problem of running, bubbling, dripping and leaking, which greatly increases the maintenance workload.

Application Overview:

Orifice flowmeter is a high-range ratio differential pressure flow device composed of a standard orifice plate with a multi-parametric differential pressure transmitter (or differential pressure transmitter, temperature transmitter and pressure transmitter), which can measure the flow rate of gas, steam, liquid and natural gas. It is widely used in process control and measurement in petroleum, chemical, metallurgy, electric power, heating, water supply and other fields.

3. Float flow meter

A float flow meter, also known as a rotor flow meter, is a variable area flow meter, in a vertical cone tube that expands from bottom to top, the gravity of the float in a circular cross-section is borne by liquid power, so that the float can rise and fall freely in the cone tube.

Float flow meter is the widest range of flow meters after differential pressure flow meters, especially in small and micro flow rates.

In the mid-80s, the sales amount of Japan, Western Europe and the United States accounted for 15%~20% of the flow meters. our country's output in 1990 was estimated to be 12~140,000 units, of which more than 95% were glass cone tube float flow meters.

Features:

(1) The glass cone tube float flowmeter has a simple structure and is easy to use, but the disadvantage is that it has low pressure resistance and a greater risk of fragile glass tubes.

(2) Suitable for small pipe diameter and low flow rate;

(3) Low pressure loss.

4. Volumetric flowmeter

Volumetric flow meter, also known as fixed displacement flow meter, referred to as PD flow meter, is the highest accuracy type in flow meters. It uses mechanical measuring elements to continuously divide the fluid into a single known volume part, and measures the total fluid volume according to the number of times the measuring chamber repeatedly fills and discharges the fluid in the volume part.

Volumetric flow meters can be divided into elliptical gear flow meters, scraper flow meters, double rotor flow meters, rotary piston flow meters, reciprocating piston flow meters, disc flow meters, liquid seal rotary cylinder flow meters, wet gas meters and membrane gas meters, etc.

Pros:

(1) High measurement accuracy;

(2) The installation pipeline conditions have no effect on the measurement accuracy;

(3) It can be used for the measurement of high-viscosity liquids;

(4) wide range;

(5) The direct-reading instrument can directly obtain the accumulation and total amount without external energy, which is clear and easy to operate.

Cons:

(1) The results are complex and large;

(2) The type, caliber and working state of the tested medium are limited;

(3) Not suitable for high and low temperature occasions;

(4) Most meters are only suitable for clean single-phase fluids;

(5) Noise and vibration are generated.

Application Overview:

Volumetric flowmeters, differential pressure flowmeters and float flowmeters are listed as the three most used flowmeters, and are often used for the total measurement of expensive media (oil, natural gas, etc.).

In recent years, the sales amount of PD flowmeters (excluding household gas meters and household water meters) in industrially developed countries has accounted for 13%~23% of flow meters; our country accounts for about 20%, and the output in 1990 (excluding household gas meters) is estimated to be 340,000 units, of which elliptical gear type and waist wheel type account for about 70% and 20% respectively.

5. Sewage flow meter

Sewage flow meters are classified according to the principle of measurement:

1. The flow meter has a throttle flow meter, a bi-custodial flow meter, a constant velocity tube flow meter, a rotor flow meter, and a target flow meter, which use the principle of Bernoulli equation to reflect the flow rate by measuring the fluid differential pressure signal;

2. The flow meter has turbine flow meter, vortex flow meter, electromagnetic flow meter, Doppler ultrasonic flow meter, and hot wire velocity flow meter, which reflect the flow rate by measuring the fluid flow velocity;

3. The flow meter has gear flow meter, scraper type flow meter, and rotary piston flow meter, which reflect the flow rate by measuring the small volume of each standard volume;

4. The flow meter has thermal mass flow meter, differential pressure mass flow meter, impeller mass flow meter, Goli mass flow meter, indirect mass flow meter, which reflects the flow rate by measuring the fluid mass;

5. The flowmeter has a weir groove flowmeter, which reflects the flow rate by measuring the liquid level.

Sewage flow meter features:

1. The sewage flow meter has a simple structure, is firm and reliable, and has a long service life.

2. There are no moving parts and resistance parts in the measuring pipe, no pressure loss, no blockage measurement is reliable, strong anti-interference ability Small size, light weight, easy installation, small maintenance, wide measurement range, measurement is not affected by fluid temperature, density, pressure, viscosity, conductivity and other changes, can be opened on the old pipeline to be renovated and installed, simple construction and installation, small engineering volume.

6. Turbine flow meter

Turbine flow meter is the main type of speed flow meter, which uses a multi-blade rotor (turbine) to feel the average flow rate of the fluid, and derives the flow rate or total amount of the meter.

Generally, it is composed of two parts: sensor and display, and can also be made into a single type.

Turbine flow meters, positive displacement flow meters, Coriolis mass flow meters are called the three types of repeatability and best precision products in flow meters, as one of the top ten types of flow meters, its products have developed to the scale of multi-variety and multi-series mass production.

Pros:

(1) High precision, among all flow meters, it is the most accurate flow meter;

(2) Good reproducibility;

(3) The element zero drift has good anti-interference ability;

(4) wide range;

(5) Compact structure.

Cons:

(1) The calibration characteristics cannot be maintained for a long time;

(2) The physical properties of the fluid have a great influence on the flow characteristics.

Application Overview:

Turbine flow meters are widely used in the following measurement objects: petroleum, organic liquids, inorganic liquids, liquefied gases, natural gas, and cryogenic fluids.

In Europe and the United States, turbine flow meters are second only to orifice flow meters in terms of usage, and the Netherlands alone has adopted more than 2,600 gas turbine flow meters of various sizes and pressures from 0.8~6.5MPa on natural gas pipelines, which have become excellent natural gas meters

7. Vortex flow meter (USF)

The vortex flowmeter is an instrument in which a non-streamlined vortex generator is placed in the fluid, and the fluid alternately separates and releases two regularly staggered vortices on both sides of the generator. When the flow section is constant, the flow rate is directly proportional to the volume flow. Therefore, the flow rate can be measured by measuring the oscillation frequency. Vortex flowmeters can be divided into stress type, strain type, capacitive type, thermal type, vibration type, photoelectric type and ultrasonic type according to the frequency detection method. This flow meter was developed and developed in the 70s. It has the advantages of both non-rotating parts and pulsed digital output, making it promising.

Pros:

(1) The vortex flowmeter has no moving parts, and the measuring element has a simple structure, reliable performance and long service life.

(2) The measurement range of the vortex flowmeter is wide. The range ratio can generally reach 1:10.

(3) The volumetric flow rate of the vortex flow meter is not affected by the thermal parameters such as temperature, pressure, density or viscosity of the measured fluid. Generally, there is no need for separate calibration. It can measure the flow rate of liquids, gases, or vapors.

(4) It causes less pressure loss.

(5) High accuracy, repeatability of 0.5%, and low maintenance.

Cons:

(1) The volumetric flow rate in the working state of the vortex flowmeter is not affected by the thermologic parameters such as temperature, pressure, and density of the measured fluid, but the final measurement result of liquid or steam should be the mass flow rate, and for gas, the final measurement result should be the standard volume flow. Both mass flow rate or standard volume flow must be converted by fluid density, and fluid density changes caused by changes in fluid conditions must be taken into account.

(2) The main factors causing flow measurement errors are: measurement errors caused by uneven flow velocity of pipelines; the medium density under fluid conditions cannot be accurately determined; Measure wet saturated steam assuming dry saturated steam. If these errors are not limited or eliminated, the total measurement error of the vortex flow meter will be large.

(3) Poor vibration resistance. External vibration will cause the vortex flow meter to produce measurement errors and even not work properly. The high flow rate impact of the channel fluid will cause additional vibration in the cantilever of the vortex generator, reducing the measurement accuracy. The influence of large pipe diameter is more obvious.

(4) Poor adaptability to measuring dirty media. The generator of the vortex flowmeter is very easy to be dirty by the medium or entangled by dirt, which changes the size of the geometry and has a great impact on the measurement accuracy.

(5) The straight pipe section has high requirements. Experts pointed out that the straight pipe 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 the fluid flow rate of media below 300°C.

USF entered industrial application in the late 60s, and since the late 80s, it has accounted for 4%~6% of the sales value of flow meters in various countries. In 1992, the estimated worldwide sales volume was 35,480 units, and the domestic products were estimated to be 8,000~9,000 units in the same period.

8. Electromagnetic Flow Meter (EMF)

The electromagnetic flowmeter is a kind of instrument made according to Faraday's law of electromagnetic induction to measure conductive liquids.

Electromagnetic flowmeters have a series of excellent characteristics that can solve the problems that are not easy to apply to other flowmeters, such as the measurement of dirty flow and corrosive flow.

In the 70s and 80s, electromagnetic flow made a major breakthrough in technology, making it a widely used type of flow meter, and its usage percentage in flow meters continued to rise.

Pros:

(1) The measuring channel is a smooth straight pipe, which will not be blocked, and is 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 not actually significantly affected by changes in fluid density, viscosity, temperature, pressure and conductivity;

(4) Large flow range and wide caliber range;

(5) Corrosive fluids can be applied.

Cons:

(1) The application of electromagnetic flowmeter has certain limitations, it can only measure the liquid flow rate of conductive media, not the flow rate of non-conductive media, such as gas and water treatment for heating water. In addition, its lining needs to be considered in high temperature conditions.

(2) The electromagnetic flowmeter determines the volumetric flow rate in the working state by measuring the speed of the conductive liquid. According to the measurement requirements, for liquid media, the mass flow rate should be measured, and the measurement of medium flow should involve the density of the fluid, which has different densities and changes with temperature. If the electromagnetic flowmeter converter does not consider fluid density, it is not appropriate to give only the volumetric flow rate at room temperature.

(3) The installation and commissioning of electromagnetic flowmeters are more complex than other flowmeters, and the requirements are stricter. Transmitters and converters must be used together, and cannot be used with two different types of meters. When installing the transmitter, from the selection of the installation site to the specific installation and commissioning, it must be carried out in strict accordance with the requirements of the product manual. The installation site should not have vibration or strong magnetic field. During installation, the transmitter and pipe must have good contact and good grounding. The potential of the transmitter is equal to the fluid being measured. When using, the gas remaining in the measuring tube must be exhausted, otherwise it will cause a large measurement error.

(4) When the electromagnetic flowmeter is used to measure viscous liquids with dirt, the viscous or sediment adheres to the inner wall or electrode of the measuring tube, causing the output potential of the transmitter to change, resulting in measurement errors, and the dirt on the electrode reaches a certain thickness, which may cause the instrument to be unable to measure.

(5) Fouling or wear of the water supply pipeline will affect the original flow value and cause measurement errors. For example, a 100mm caliber instrument inner diameter change of 1mm 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 is also mixed with some signals that have nothing to do with the flow rate, such as phase voltage, quadrature voltage and common mode voltage. To accurately measure the flow rate, it is necessary to eliminate various interference signals and amplify the flow signal effectively. The performance of the flow converter should be improved, it is best to use a micro-processing converter, use it to control the excitation voltage, and select the excitation mode and frequency according to the properties of the measured fluid, which can eliminate in-phase interference and orthogonal interference. However, the improved instrument structure is complex and costly.

(7) The price is higher

Application Overview:

Electromagnetic flowmeters have a wide range of applications, and large-diameter instruments are mostly used in water supply and drainage projects. Small and medium-sized diameters are often used in high-demand or difficult-to-measure occasions, such as blast furnace cooling water control in the iron and steel industry, measurement of pulp liquid and black liquor in the paper industry, strong corrosive fluid in the chemical industry, and mineral slurry in the non-ferrous metallurgical industry. Small caliber and small caliber are often used in pharmaceutical industry, food industry, biochemistry and other places with hygiene requirements. Since EMF entered industrial application in the early 50s, its use has expanded day by day, accounting for 16%~20% of the sales of flow meters in various countries since the late 80s. our country has developed rapidly in recent years, with sales estimated at 6500~7500 units in 1994. China has produced ENF with a maximum diameter of 2~6m, and has the equipment capacity of 3m for real-current calibration.

9. Ultrasonic flowmeter

Ultrasonic flow meters are designed based on the principle that the speed of ultrasonic waves propagating in a flowing medium is equal to the geometric sum of the average flow velocity of the measured medium and the velocity of the sound wave itself. It is also measured by measuring the flow rate to reflect the flow size. Although the ultrasonic flowmeter only appeared in the 70s, it is very popular because it can be made into a non-contact type and can be linked with an ultrasonic water level gauge to measure the opening flow, without causing disturbance and resistance to the fluid.

Ultrasonic flowmeters can be divided into time difference type and Doppler type according to the measurement principle

The time-difference ultrasonic flowmeter manufactured by the principle of time difference has received widespread attention and use in recent years, and is currently the most used ultrasonic flowmeter in enterprises and institutions.

Ultrasonic Doppler flow meters manufactured by Doppler effect are mostly used to measure suspended particles or bubble medium in the medium, and their use has certain limitations, but it solves the problem that time-lagged ultrasonic flow meters can only measure a single clear fluid, and are also considered to be ideal instruments for non-contact measurement of two-phase flow.

Pros:

(1) Ultrasonic flowmeter is a non-contact measuring instrument, which can be used to measure fluid flow and large pipe runoff that are not easy to contact and observe. It does not alter the flow state of the fluid, does not cause pressure loss, and is easy to install.

(2) It can measure the flow rate of strong corrosive media and non-conductive media.

(3) The measurement range of the ultrasonic flowmeter is large, and the pipe diameter ranges from 20mm~5m.

(4) Ultrasonic flow meters can measure various liquid and sewage flows.

(5) The volumetric flow measured by the ultrasonic flowmeter is not affected by the thermophysical parameters such as temperature, pressure, viscosity and density of the measured fluid. It can be made in both fixed and portable forms.

Cons:

(1) The temperature measurement range of ultrasonic flowmeters is not high, and generally only can measure fluids with a temperature below 200°C.

(2) Poor anti-interference ability. It is susceptible to ultrasonic noise interference mixed in by bubbles, fouling, pumps and other sound sources, and affects the measurement accuracy.

(3) The requirements of the straight pipe section are strict, which is 20D in the front and 5D in the back. Otherwise, the discreteness is poor and the measurement accuracy is low.

(4) The uncertainty of installation will bring large errors to the flow measurement.

(5) Due to fouling of the measuring pipeline, it will seriously affect the measurement accuracy, bring significant measurement errors, and even in severe cases, the instrument will not display the flow

(6) The reliability and accuracy level are not high (generally about 1.5~2.5 levels), and the repeatability is poor.

(7) Short service life (general accuracy can only be guaranteed for one year).

(8) Ultrasonic flow meter is to determine the volume flow rate by measuring the fluid velocity, for the liquid should measure its mass flow, the instrument measures the mass flow rate is obtained by multiplying the volume flow by the artificially set density, when the fluid temperature changes, the fluid density is changed, the density value is artificially set, and the accuracy of the mass flow cannot be guaranteed. Only by measuring the fluid velocity and measuring the fluid density can the real mass flow 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 fluid, strange liquid, liquefied natural gas, etc.; In terms of gas applications, it has good experience in the field of high-pressure natural gas;

The Doppler method is suitable for biphase fluids with not too high out-of-phase content, such as: untreated sewage, plant effluent, dirty process fluid; Generally not suitable for very clean liquids.

10. Mass flow meter

Since the volume of the fluid is affected by temperature, pressure and other parameters, the parameters of the medium need to be given when the volume flow is expressed by the volumetric flow. In the case of constantly changing media parameters, it is often difficult to meet this requirement, resulting in distortion of the instrument display value. Therefore, mass flow meters have been widely used and valued. There are two types of mass flow metering and scoring: direct and indirect. Direct mass flow meters use the principle directly related to mass flow to measure, and commonly used mass flow meters include calorimetry, angular momentum, vibration gyroscope, Magnus effect and Coriolis force type. The indirect mass flow meter uses the density meter to directly multiply the volumetric flow rate to obtain the mass flow rate.

In modern industrial production, the temperature, pressure and other operating parameters of the flowing fluid are constantly improving, and in the case of high temperature and high pressure, due to the material and structure, the application of direct mass flow meters encounters difficulties, while indirect mass flow meters are often not easy to apply due to the limitation of humidity and pressure application range of density meters. Therefore, temperature and pressure compensated mass flow meters are widely used in industrial production. It can be regarded as an indirect mass flow meter, not with a density meter, but by using the relationship between temperature, pressure and density, the temperature and pressure signals are calculated as density signals by function, and the mass flow is obtained by multiplying them with the volumetric flow. Although the temperature and pressure compensated mass flow meter has been put into practice, it is difficult or impossible to compensate correctly when the parameters of the measured medium change large or very rapidly, so further research on mass flow meters and density meters applicable in actual production is still a topic.

11. Throttle flow meter

There is a throttle device on the gas flow pipeline, which is equipped with an orifice plate, and there is a round hole in the center, the pore diameter is smaller than the inner diameter of the pipe, and the gas flows steadily forward in front of the orifice, and when the gas flows through the orifice, the pore size becomes smaller, the cross-sectional area shrinks, so that the stable flow state is disrupted, so the flow rate will change, the speed will be accelerated, and the static pressure of the gas will decrease, so the pressure will fall before and after the orifice, that is, the differential pressure (the pressure is large where the front section of the orifice plate is large, and the pressure is small where the cross-section through the orifice plate is small). The size of the differential pressure has a definite numerical relationship with the gas flow, that is, when the flow rate is large, the differential pressure is large, and when the flow rate is small, the differential pressure is small. The flow rate is proportional to the square root of the differential pressure. A throttle flow meter is a meter that calculates flow rate based on the differential pressure, known fluid conditions, and geometric dimensions of the test part and pipeline generated by the flow detector installed in the pipeline.

Features:

The throttle flow meter is a typical differential pressure flow meter. It is the most commonly used flow meter used to measure the flow rate of gases, liquids and vapors in industrial production. According to the survey and statistics, about (70-80)% of the flow meters used in industrial production systems such as steel mills and oil refineries are throttling flow meters. In the entire industrial production field, throttling flow meters also account for more than half of the total number of flow meters. The throttle flow meter is so widely used mainly because it has the following two very outstanding advantages:

The structure is simple, easy to install, reliable work, low cost, and has a certain accuracy. It can meet the needs of engineering measurement.

It has a long history of use, rich and reliable experimental data, and the design and processing have been standardized. As long as the throttle flow meter is designed and processed according to the standard, the flow measurement can be carried out within the known uncertainty range without actual calibration.

Especially the second advantage, which makes the throttle flow meter very convenient in manufacturing and use. Because a flow meter, especially the flow juice used for large flow measurement, will encounter various difficulties in verification.

12. Nozzle flow meter

Nozzle flow meter is a differential pressure generator that measures the flow rate, and can measure the flow rate of various fluids in the pipeline with various differential pressure meters or differential pressure transmitters. The standard nozzle throttle device is used in conjunction with the differential pressure transmitter, which can measure the flow rate of liquid, steam and gas, and is widely used in petroleum, chemical, metallurgy, electric power, light industry and other departments.

The integrated installation consists of an intelligent display (multi-uneven transmitter) and a nozzle device to form a nozzle flow meter. It comes with high-quality differential pressure sensor, pressure sensor, thermal resistance temperature sensor. AW2003- intelligent display (multi-uneven transmitter) not only automatically adapts to the range of differential pressure sensor, but also calculates various compensation coefficients such as outflow coefficient C, beam expansion coefficient ε, etc., which truly expands the range and ensures the accuracy of measurement. The large screen LCD is used to display the cumulative flow, instantaneous flow, instantaneous pressure, and instantaneous temperature value on the same screen, without manual switching. 4-20mA two-wire instantaneous flow output. It is divided into two categories: intrinsically safe explosion-proof products and ordinary products. The split installation consists of a combination of independent nozzle device, differential pressure, pressure, temperature transmitter, flow calculator, shut-off valve, etc. The connection between the parts is done by the user himself.

Features:

Compared with orifice flow meters, nozzle flow meters have less pressure loss, so they save energy, are more robust and durable, suitable for high temperature and high pressure fluids, and are widely used in electric power, chemical and other industries for steam flow measurement. Nozzle flow meters include two types: standard nozzles (ISA1932 nozzles) and long neck nozzles. Its design and manufacturing comply with the provisions of international standards ISO5167 or national standards GB/T2624.

13. Target flowmeter

Target flowmeter began to be used in industrial flow measurement in the sixties, mainly used to solve the flow measurement of high viscosity, low Reynolds number fluid, has experienced two major stages of development of pneumatic meters and electric meters, SBL series intelligent target flowmeter is based on the original strain gauge (capacitive) target flowmeter measurement principle, the latest force sensing sensor as the measurement and sensitive transmission element, and the use of modern digital intelligent processing technology to develop a new flow metering instrument.

Features:

1. The whole instrument structure is solid and has no moving parts, and the plug-in structure is easy to disassemble.

2. A variety of anti-corrosion and high and low temperature resistant materials (such as Hastelloy, titanium, etc.) can be selected;

3. The whole machine can be made into a complete seal without dead angles (welding form), without any leakage points, and can withstand 42MPa high pressure;

4. The instrument is equipped with a self-test program, and the fault phenomenon is clear at a glance;

5. The sensor does not come into contact with the measured medium, there is no wear of parts, and it is safe and reliable to use.

6. The dry calibration method can be used on the spot, that is, the weight hanging weight method. Single-button operation can complete the calibration;

7. There are a variety of installation methods to choose from, such as choosing online plug-in type, low installation cost;

8. It has integrated temperature and pressure compensation, and directly outputs the quality or standard square;

9. It has optional small signal cutting, nonlinear correction, and filtering time.

10. It can accurately measure the flow rate of gas and liquid at various normal temperature, high temperature 500 degrees, and low temperature -200 degrees;

11. Accurate measurement, accuracy can reach 0.2%;

12. Good repeatability, generally 0.05%~0.08%, fast measurement;

13. The pressure loss is small, only about 1/2△P of the standard orifice plate;

14. Anti-interference and impurity resistance;

15. The range can be changed by replacing the current blocker (target piece) according to actual needs;

16. The low-power battery on-site display can read the value directly online, and the display screen can read the instantaneous and cumulative flow rate and percentage bar graph at the same time;

17. Simple and convenient installation, very easy to maintain;

18. A variety of output forms, which can transmit various parameters far away;

19. Strong vibration resistance, pulsating flow can be measured within a certain range.

14. Twin rotor gas flow meter

The double rotor flow meter belongs to the latest generation of positive displacement flow meter in the world, also known as UF-‖ flow meter or screw flow meter. It is a precision instrument used for the measurement and control of liquid flow in pipelines. It is widely used in petroleum, chemical, metallurgy, electric power, transportation, ships, oil depots, terminals, tank trucks and other departments, especially suitable for crude oil, refined oil, light hydrocarbons and other industrial liquids of metering flowmeters can be indicated on site, the word code can be read directly and can be equipped with transmitters, output electrical pulse signals, and transmit to secondary instruments or computers remotely to form automatic control, automatic detection and data processing systems.

Features:

It is suitable for thin oil, light oil, heavy oil, crude oil with large sand content and large water content, and the viscosity range of the measured liquid is large.

The flow rate of liquid through the flowmeter is large, and the maximum flow rate is about twice that of the ordinary volume table of the same diameter.

Long service life, high accuracy and strong reliability.

The in-compression loss is minimal.

The longest distance of wired teletransmission is 1000 meters, and the pulse signal output is N=0.1L (one pulse is 1N), which can be directly connected to the computer.

15. Vertical waist wheel flow meter

The waist wheel flow meter, also known as the roots flow meter, has the following structural characteristics: there is a metering chamber in the casing of the flow meter, and there is a pair or two pairs of waist wheels that can rotate tangentially in the metering chamber. A pair of transmission gears are installed coaxically with the two search wheels outside the flowmeter housing, which mesh, so that the two waist wheels can be linked to each other. The waist wheel flow meter can be used for flow measurement of various clean liquids, especially for oil measurement, and can also be used as a flow meter for measuring gases. It has the highest accuracy of 0.1-0.5 levels.

Features:

The waist wheel flow meter product has a novel design and beautiful appearance. It has the characteristics of light weight, high precision, and easy installation and use. It is one of the typical products of positive displacement flow meters. Its main disadvantages are: large size and bulkiness. The pressure loss is large. large vibration during operation, etc. The use of two pairs of waist wheel structures at an angle of 45 degrees can greatly reduce the vibration and noise during operation.

16. Venturi flow meter

The basic measurement principle of the new generation of differential pressure flow measuring instrument is a flow measurement method based on the law of conservation of energy - the Bo effort equation and the flow continuity equation. The Neventuri tube consists of a circular measuring tube and a special core placed in the measuring tube and coaxial with the measuring tube. The radial outer surface of the special core has a geometric profile similar to the inner surface of a classic venturi tube and forms a reduced annular overflow gap between it and the inner surface of the measuring tube. The throttling process of fluid flowing through the inner venturi tube is basically similar to that of the fluid flowing through the classic venturi tube and annular orifice plate. This structural feature of the venturi tube makes it not have the problem of sharp edge wear and fouling accumulation similar to that of orifice throttle parts during use, and can effectively adjust the flow (rectification) of the fluid velocity distribution gradient in the tube before throttling and various non-axisymmetric velocity distributions that may exist, so as to achieve high accuracy and high stability of flow measurement.

Features:

Advantages: If it can be manufactured accurately in accordance with ASME standards, the measurement accuracy can also reach 0.5%, but the domestic venturi due to its manufacturing technology problems, the accuracy is difficult to guarantee, the domestic old qualification of the strong technical force of Kaifeng instrument factory can only ensure 4% measurement accuracy, for the working conditions of ultra-supercritical power generation, the pressure equalization ring at this pipe is a very dangerous link to use at high temperature and high pressure, without the use of the pressure equalization ring, it does not meet the ASNEISO5167 standards, and the measurement accuracy cannot be guaranteed. This is a contradiction in the manufacture of high-voltage classic venturis.

Disadvantages: The pipe is made of the same material as the inlet/outlet, and the fluid washes and wears the pipe seriously, which cannot ensure long-term measurement accuracy. The length of the structure must be manufactured in accordance with ISO-5167, otherwise the required accuracy will not be achieved, due to the strict structural regulations of ISO-5167 for the classic venturi, its flow measurement range is very small, generally between 3–5. It is difficult to meet the flow measurement with large flow fluctuations.

17. Thermal mass flow meter (constant temperature difference TMF)

Pros:

(1) Ball valve installation, easy to install and disassemble. And can be installed with pressure.

(2) Based on Guinness's law, the mass flow rate is directly measured. The measured values are not affected by pressure and temperature.

(3) Respond quickly.

(4) The range of measurement range is large, and the minimum flow rate of the pipeline can be measured by 8.8mm and the maximum can be measured by 30''

(5) Plug-in type flow meter, one flow meter can be used to measure a variety of pipe diameters.

Cons:

(1) The accuracy is not as good as other types of flow meters, generally 3%.

(2) The scope of application is narrow, and it can only be used to measure dry non-explosive gases, such as compressed air, nitrogen, argon and other neutral gases.

18. Coriolis mass flow meter (CMF)

Coriolis mass flow meter (hereinafter referred to as CMF) is a direct mass flow meter made by using the Coriolis force principle that is proportional to the mass flow rate when the fluid flows in a vibrating tube.

The application of CMF in our country started late, and in recent years, several manufacturers (such as Taihang Instrument Factory) have developed their own supply markets; There are also several manufacturing plants that have formed joint ventures or used foreign technology to produce a series of instruments.

Foreign CMF has developed more than 30 series, and the technical focus of each series is on the design and innovation of the flow detection and measurement tube structure; improve the stability and accuracy of the instrument's zero point; increase the deflection of the measuring tube to improve the sensitivity; Improve the stress distribution of the measuring tube, reduce fatigue damage, and strengthen the ability to resist vibration interference.

19. Open channel flow meter

Unlike the previous ones, it is a flow meter that measures the natural flow of free surfaces in a non-full tube-like open channel.

A waterway that flows in a non-full pipe state is called an open channel, and the water flow in an open channel is called an open channel flow meter.

In addition to round, open channel flowmeters also have U-shaped, trapezoidal, rectangular and other shapes.

All urban water supply diversion canals in the application field of open channel flowmeter; water diversion and drainage channels of thermal power plants, sewage treatment inflow and discharge channels; water discharge of industrial and mining enterprises, as well as channels for water conservancy projects and agricultural irrigation. Some people estimate that 1995 units, accounting for about 1.6% of the total flow meters, but there is no estimated data for domestic applications.

20、静电流量计(electrostaticflowmeter)

Tokyo Institute of Technology in Japan has developed an electrostatic flow meter suitable for low conductive liquid flow measurement in oil transmission pipelines.

The metal measuring tube of the electrostatic flowmeter is insulated and connected to the pipe system, and the electrostatic charge on the measuring capacitor can know the charge in the measuring tube. They conducted a real-flow test on metal and plastic measuring tubes with an inner diameter of 4~8mm copper, stainless steel, etc., and the test showed that the flow rate and charge were close to linear.

21、复合效应流量仪表(combinedeffectsmeter)

The working principle of the meter is based on the momentum and pressure of the fluid acting on the deformation generated by the instrument cavity, and the deformation of the compound effect is measured to obtain the flow rate. This meter was developed by the GMI School of Engineering and Management in the United States and has applied for two patents.

22. Tachmetric flowratesensor

It was developed by the Russian Scientific and Engineering Center Industrial Instrumentation Company and was developed based on the theory of the suspension effect. The meter has been successfully used in several sites (e.g. more than 2,000 units for measuring hot water flow in a nuclear power plant for 8 years) and are being improved to expand the range of applications