The nozzle flowmeter is a differential pressure generating device for measuring the flow rate, and can cooperate with various differential pressure gauges or differential pressure transmitters to measure the flow of various fluids in the pipeline. The standard nozzle throttling device is used in conjunction with a differential pressure transmitter to measure the flow of liquids, vapors, and gases. It is widely used in petroleum, chemical, metallurgy, electric power, and light industry sectors.
Integral installation consists of a smart meter (multi-variable transmitter) and a nozzle device to form a nozzle flow meter. It comes with a high-quality differential pressure sensor, pressure sensor, thermal resistance temperature sensor. AW2003-type intelligent display instrument (multi-variance transmitter) not only automatically adapts to the range of differential pressure sensor, but also various compensating factors such as: outflow coefficient C, flow expansion coefficient ε, etc. Range while ensuring the accuracy of measurement. The large-screen LCD displays the cumulative flow, instantaneous flow, instantaneous pressure, and instantaneous temperature on the same screen without manual switching. 4-20mA two-wire instantaneous flow output. Two types of intrinsically safe explosion-proof products and ordinary products. The split type installation consists of an independent nozzle unit, differential pressure, pressure, temperature transmitter, flow calculator, and cut-off valve. The connection between the various parts is completed by the user himself.
Features:
Compared with orifice flowmeters, nozzle flowmeters have less pressure loss, thus saving energy, are more robust and durable, are suitable for high temperature and high pressure fluids, and are widely used in the measurement of steam flow in power, chemical and other industries. Nozzle flow meter includes standard nozzle (ISA1932 nozzle) and long neck nozzle. Its design and manufacture are in line with the international standard ISO5167 or the national standard GB/T2624.
13 target flowmeter
   
The target flow meter was applied to the industrial flow measurement in the 1960s, mainly used to solve the flow measurement of high viscosity, low Reynolds number fluids. It has experienced two major development stages: aerodynamic meter and electric meter. The smart target flow meter is in the original Based on the measuring principle of the strain gauge type (capacitive) target flow meter, a new type of flow meter is developed using the latest type of force-sensitive sensor as a measurement and sensitive transmission element while utilizing modern digital intelligent processing technology. .
Features:
1, the entire instrument structure is solid and no moving parts, plug-in structure, easy removal;
2, can choose to use a variety of anti-corrosion and high and low temperature materials (such as Hastelloy, titanium, etc.);
3, the whole machine can be made completely sealed without dead ends (welding form), without any leakage point, can withstand 42MPa high pressure;
4, the instrument has a self-test program, the phenomenon of failure at a glance;
5, the sensor does not contact with the measured medium, there is no wear parts, the use of safe and reliable;
6, dry calibration method can be used on the spot, that is, using weight hanging method. One-button operation can complete the calibration;
7, with a variety of installation options for selection, such as the choice of online plug-in, low installation costs;
8, with integrated temperature, pressure compensation, direct output quality or standard;
9, with optional small signal removal, nonlinear correction, filter time can be selected;
10. It can accurately measure the gas and liquid flow under various normal temperature, high temperature 500 degrees, low temperature -200 degrees;
11, accurate measurement, accuracy can reach 0.2%;
12, good repeatability, generally 0.05% to 0.08%, rapid measurement;
13, the pressure loss is small, only about 1/2 â–³ P of the standard orifice plate;
14, anti-interference, anti-impact ability is particularly strong;
15, according to the actual need to replace the flow block (target) and change the range;
16, low-power battery field display, online direct reading indication, the display can read instantaneous and cumulative flow and percentage of bar graph;
17, easy to install, easy to maintain;
18, a variety of output forms, can remotely transmit various parameters;
19, anti-vibration, a certain range of pulsating flow can be measured.
14 dual rotor gas flowmeter
   
Dual-rotor flowmeters are the latest generation of positive displacement flowmeters in the world, also known as UF-‖ flowmeters or screw flowmeters. It is a precision instrument for the measurement and control of liquid flow in pipes. Widely used in petroleum, chemical, metallurgy, electric power, transportation, ships, oil depots, docks, tanker trucks and other departments, especially for measuring flowmeters for industrial liquids such as crude oil, refined oil, and light hydrocarbons. Can be equipped with the transmitter, the output of electrical pulse signal, remote transmission to the secondary instrument or computer, composed of automatic control, automatic detection and data processing systems.
Features:
Applicable to thin oil, light oil, heavy oil, crude oil with large sand content and large water content, the range of viscosity of the liquid to be measured is large.
The flow rate of the fluid passing through the flowmeter is large, and the maximum flow rate is about twice that of the normal volume table of the same path.
Long service life, high accuracy and reliability.
The loss within the pressure is minimal.
The longest distance for wired remote transmission is 1000 meters, and the pulse signal output is N=0.1L (one pulse is 1N), which can be directly connected to a computer.
15 vertical waist flowmeter
   
With so many flow meters, these motion pictures give you a full understanding
The flowmeter is a commonly used measuring instrument. The flowmeter has high measurement accuracy, good stability, and convenient use. There are certain applications in many fields. There are many kinds of flowmeters, and the function and measurement range of each different flowmeter are different. So how much is the specific flow meter classification? What are the disadvantages and applications of each flow meter?
Flowmeter classification
Meters measuring fluid flow are collectively referred to as flow meters or flow meters. Flowmeter is one of the most 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 flowmeters have come out one after another. More than 100 meters have been put into use.
Each product has its specific applicability and it also has its limitations. According to the principle of measurement, there are mechanics principle, thermal principle, acoustic principle, electrical principle, optical principle and atomic physics principle.
According to the principle of flow meter structure classification. Volumetric flowmeters, differential pressure flowmeters, floatometers, turbine flowmeters, electromagnetic flowmeters, vortex flowmeters, mass flowmeters, and plug-in flowmeters in fluidic oscillators.
According to the measurement object, there are two types of closed pipes and open channels; according to the purpose of measurement, they can be divided into total measurement and flow measurement, and the meters are called total meters and flow meters, respectively. Aggregate meters measure the flow through a pipeline over a period of time, expressed as a quotient of the total amount of flow in a short period of time divided by that time. Actually, a flow meter is usually equipped with a cumulative flow device for use as a total gauge. The total volume table also has a traffic signalling device. Therefore, dividing the flowmeter and the total amount table in a strict sense has no practical significance.
First, classified by measuring principle
1. Mechanics: The instruments belonging to this type of principle are the differential pressure type and rotor type utilizing Bernoulli's theorem; the impulse type and movable tube type using momentum theorem; the direct mass type using Newton's second law; and the use of fluid momentum. The target of the principle, the turbine type using the angular momentum theorem, the vortex type and the vortex type using the fluid oscillation principle, the Pitot tube type using the total static pressure difference, and the volumetric type enthalpy, trough, and the like.
2. Electrical principles: Instruments used for this type of principle include electromagnetic, differential capacitance, inductive, and strain resistive.
3. Acoustic principle: Ultrasonic type is used for flow measurement using acoustic principle. Acoustic type (shock wave type) etc.
4. Thermal principle: The use of thermal principles to measure the flow of the thermal type, direct calorimeter, indirect calorimeter and so on.
5. Optical principle: Laser type, photoelectric type, etc. are instruments that belong to this type of principle.
6. Original in the physical principles: nuclear magnetic resonance, nuclear radiation, etc. are the instruments that belong to this principle.
7. Other principles: There are marking principles (tracing principle, nuclear magnetic resonance principle), relevant principles and so on.
Second, according to the structure of the flow meter structure classification
According to the actual situation of the current flowmeter products, according to the structure 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 detection element installed in the pipeline, the known fluid condition, and the geometry of the detection element and the pipeline.
The differential pressure flowmeter consists of a primary device (test piece) and a secondary device (differential pressure conversion and flow display instrument). Differential pressure flowmeters are often classified in the form of test pieces, such as orifice flowmeters, venturi flowmeters, and equal velocity tube 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 specification, serialization, generalization and standardization. It can measure flow parameters as well as other parameters (such as pressure, level, density, etc.) ).
Differential pressure flow meter detection parts according to its role can be divided into: throttling device, hydraulic resistance type, centrifugal, dynamic pressure head type, dynamic pressure head gain type and jet type several categories.
Detectors can be divided into two categories according to their degree of standardization: standard and non-standard.
The so-called standard test pieces are designed, manufactured, installed and used as long as they are in accordance with standard documents, and the flow values ​​and estimated measurement errors can be determined without real-flow calibration.
Non-standard test pieces are of poor maturity and have not been included in international standards.
Differential pressure flowmeter is one of the most widely used flowmeters, and it ranks first in the use of various types of flow meters. In recent years, due to the advent of various new flowmeters, the percentage of its use has gradually declined, but it is still the most important type of flowmeter.
advantage:
(1) The most widely used perforated plate flowmeter has a strong structure, stable and reliable performance, and long service life;
(2) It has a wide range of applications. No flowmeter has yet been compared with it.
(3) The detection parts, transmitters and display meters are produced by different manufacturers respectively, which is convenient for economies of scale production.
Disadvantages:
(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 (finger plates, nozzles, etc.).
Application Overview:
Differential pressure flowmeters have a particularly wide range of applications and have applications in flow measurement of closed pipes, such as fluids: single-phase, mixed-phase, clean, dirty, viscous flow, etc.; work status: normal pressure, high pressure , vacuum, room temperature, high temperature, low temperature, etc.; pipe diameter: from a few mm to several m; flow conditions: subsonic, sonic, pulsating flow. Its consumption in various industrial sectors accounts for about 1/4 to 1/3 of the total flow meter usage.
2 orifice flowmeter
　    
advantage:
The standard throttling device is universal in the world and has been approved by the international standard organization. It can be used without real-time calibration, and it is also unique in the flowmeter. The structure is easy to copy, simple, firm, stable and reliable performance, low price;
   
Disadvantages:
The reproducibility and accuracy of the measurement are of medium level in the flowmeter, and the accuracy is difficult to improve due to the intricacies of numerous factors. The range is narrow. Because the flow coefficient is related to the Reynolds number, the general range is only 3:1 to 4:1. With long straight pipe length requirements, it is generally difficult to meet. Especially for larger pipe diameters, the problem is even more pronounced; pressure loss is large; in order to maintain the normal operation of an orifice plate flow meter, the pump needs additional power to overcome the pressure loss of the orifice plate.
The accuracy of the hole is ensured by the acute angle of the inner hole, so it is sensitive to corrosion, abrasion, scaling, and dirt. It is difficult to ensure long-term use accuracy. It is necessary to remove the strong inspection once a year. The use of flanged connections can easily cause run, run, drip and leak problems, which greatly increases maintenance workload.
Application Overview:
Orifice flowmeter is a high-range differential pressure flow device which is composed of standard orifice plate and multi-parameter differential pressure transmitter (or differential pressure transmitter, temperature transmitter and pressure transmitter), and can measure gas and steam. The flow of liquids and natural gas. Widely used in petroleum, chemical, metallurgy, electricity, heating, water supply and other areas of process control and measurement.
3 float flow meter
A float flowmeter, also known as a rotameter, is a type of variable area flowmeter. In a vertical conical tube that expands from bottom to top, the gravity of a float of circular cross-section is subjected to hydrodynamic forces, so that the float It can rise and fall freely in the cone.
The float flow meter is the second most widely used type of flow meter after the differential pressure flow meter, and plays an important role in the small and micro flow.
In the mid-1980s, sales in Japan, Western Europe and the United States accounted for 15% to 20% of the flow meters. China's production in 1990 was estimated at 12 to 140,000 units, of which more than 95% were glass cone floater flowmeters.
Features:
(1) The glass cone floater flowmeter has a simple structure and is easy to use. The disadvantage is that the pressure resistance is low, and there is a large risk that the glass tube is fragile;
(2) Suitable for small diameter and low flow rate;
(3) Low pressure loss.
4 volumetric flow meters
   
   
Volumetric flowmeters, also known as fixed displacement flowmeters, referred to as PD flowmeters, are the most accurate type of flowmeters. It uses a mechanical measuring element to continuously divide the fluid into a single known volume fraction, measuring the total volume of fluid according to the number of times that the measurement chamber fills and discharges the volume fraction of fluid sequentially and repeatedly.
Volumetric flowmeters are classified according to their measuring components and can be divided into oval gear flowmeters, scraper flowmeters, dual-rotor flowmeters, rotary piston flowmeters, reciprocating piston flowmeters, disk flowmeters, liquid-sealing tumbler flowmeters. Wet gas meter and film gas meter.
advantage:
(1) High measurement accuracy;
(2) Installation pipeline conditions have no effect on the measurement accuracy;
(3) can be used for the measurement of high viscosity liquids;
(4) Wide range;
(5) Direct-reading meters can be directly accumulated, total, clear, and easy to operate without external energy.
Disadvantages:
(1) The result is complex and bulky;
(2) The types of medium to be measured, the caliber, and the working status of the medium are more limited;
(3) Not suitable for high and low temperature applications;
(4) Most meters are only suitable for clean single-phase fluids;
(5) Generate noise and vibration.
Application Overview:
Volumetric flowmeters and differential pressure flowmeters and float flowmeters are listed as the three most used flowmeters and are often used for the measurement of the total amount of expensive media (oil, natural gas, etc.).
In industrialized countries, PD flowmeters (excluding domestic gas meters and household water meters) accounted for 13%~23% of the flow meters in recent years; China accounted for about 20%; the 1990 production (excluding domestic gas meters) was estimated at 340,000. Taiwan, where the 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. Flowmeters include throttling flowmeters, bicombeflow flowmeters, constant velocity tube flowmeters, rotameters, and target flowmeters. These flowmeters use the principle of Bernoulli's equation to measure flow through differential pressure signals. ;
2. Flowmeters include turbine flowmeters, vortex flowmeters, electromagnetic flowmeters, Doppler ultrasonic flowmeters, and hot wire flowmeters, which measure flow rates by measuring fluid flow.
3, the flowmeter has a gear type flowmeter, scraper type flowmeter, rotary piston type flowmeter, which is measured by a small volume of standard volume to reflect the flow;
4. Flowmeters have thermal mass flowmeters, differential pressure mass flowmeters, impeller mass flowmeters, Coriolis mass flowmeters, and indirect mass flowmeters, which reflect flow by measuring fluid quality;
5. The flowmeter has a gutter-type flowmeter, which measures the flow by measuring the liquid level.
Sewage flow meter features:
1. The sewage flow meter 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 obstruction and reliable measurement, strong anti-jamming capability, small size, light weight, easy installation, low maintenance, wide measuring range, and no temperature, density measurement The effects of changes in pressure, viscosity, conductivity, etc., can be retrofitted and installed on old pipes, and the construction and installation are simple and the amount of work is small.
6 turbine flowmeter
   
   
　　
7 Vortex Flowmeter (USF)
   
The vortex flowmeter is a non-streamlined vortex generator placed in the fluid. The fluid is alternately separated on both sides of the generator to release two series of regularly staggered vortices. When the flow cross-section is constant, the flow rate is proportional to the flow of the lead volume. Therefore, measuring the oscillation frequency can measure the flow. Vortex flowmeter according to the frequency detection method can be divided into: stress type, strain type, capacitive type, thermal type, vibration type, photoelectric type and ultrasonic type. This flow meter was developed and developed in the 1970s. Because it has the advantages of no rotating parts and pulsed digital output, it has a promising future.
advantage
(1) The vortex flowmeter has no movable parts and the measuring element has a simple structure, reliable performance and long service life.
(2) Vortex flowmeter has a wide measuring range. The range ratio can generally reach 1:10.
(3) The volumetric flow rate of vortex flowmeters is not affected by thermal parameters such as temperature, pressure, density, or viscosity of the fluid being measured. Generally do not need to be calibrated separately. It can measure the flow of liquids, gases or steam.
(4) It has a small pressure loss.
(5) High accuracy, repeatability of 0.5%, and low maintenance.
Shortcomings
(1) The volumetric flow rate of a vortex flowmeter is not affected by thermal parameters such as temperature, pressure, and density of the fluid being measured. However, the final measurement result of liquid or steam should be mass flow. For gases, the final measurement result should be Is the standard volume flow. Mass flow or standard volumetric flow must be scaled by fluid density. Fluid density changes due to changes in fluid conditions must be considered.
(2) The main causes of flow measurement error are: measurement error caused by uneven flow velocity of the pipeline; inability to accurately determine the density of the medium when the fluid working conditions change; and to assume that wet saturated steam is measured as dry saturated steam. If these errors are not limited or eliminated, the total measurement error of vortex flowmeters will be large.
(3) Poor vibration resistance. External vibrations can cause vortex flowmeters to produce measurement errors, and may not even function properly. The impact of high flow velocity in the channel fluid will cause additional vibration in the cantilever of the vortex generator body, which will reduce the measurement accuracy. The influence of large diameter is even more pronounced.
(4) poor adaptability to measure dirty media. The body of the vortex flowmeter is easily contaminated with dirt or entangled with dirt, changing the size of the geometry and greatly affecting the measurement accuracy.
(5) High requirements for straight sections. Experts pointed out that the straight section of the vortex flowmeter must ensure 20D after the first 40D to meet the measurement requirements.
(6) Poor temperature resistance. Vortex flowmeters typically measure only fluid flow below 300°C.
USF entered industrial applications in the late 1960s, and it accounted for 4% to 6% of the total sales volume of flow meters in various countries since the late 1980s. In 1992, the estimated worldwide sales volume was 3.548 million units, and domestic products were estimated at 8,000-9,000 units during the same period.
8 electromagnetic flowmeter (EMF)
   
　　
Electromagnetic flowmeters are meters that measure conductive liquids based on Faraday’s electromagnetic induction law.
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 70s and 80s, there was a major technological breakthrough in electromagnetic flow, making it a widely used type of flowmeter, and the percentage of its use in flow meters has been increasing.
advantage:
(1) The measurement channel is a smooth, straight tube that will not block and is suitable for the measurement of liquid-solid two-phase fluids containing solid particles, such as pulp, sludge, sewage, etc.;
(2) No pressure loss caused by flow detection, energy saving effect is good;
(3) The measured volumetric flow is virtually unaffected by changes in fluid density, viscosity, temperature, pressure, and conductivity;
(4) Large flow range and wide caliber range;
(5) Corrosive fluids may be applied.
Disadvantages:
(1) The application of the electromagnetic flowmeter has certain limitations. It can only measure the liquid flow of the conductive medium, and cannot measure the flow of non-conductive medium, such as gas and water heating water. In addition, its lining needs to be considered under high temperature conditions.
(2) The electromagnetic flowmeter determines the volumetric flow under working conditions by measuring the speed of the conductive liquid. According to the measurement requirements, for the liquid medium, the mass flow should be measured. The measurement of the medium flow should involve the density of the fluid. Different fluid media have different densities and change with temperature. If the electromagnetic flowmeter converter does not consider the 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 complicated than other flowmeters and require stricter requirements. Transmitters and converters must be used together. Two different types of meters cannot be used between them. When installing the transmitter, from the choice of installation site to the specific installation and commissioning, must strictly follow the product specification requirements. There must be no vibration and no strong magnetic field at the installation site. The transmitter and pipe must have good contact and good grounding during installation. The potential of the transmitter is equal to the fluid being measured. In use, the gas remaining in the measuring tube must be drained, otherwise it will cause a larger measurement error.
(4) When the electromagnetic flowmeter is used to measure viscous liquid with dirt, stickies or deposits adhere to the inner wall or electrode of the measuring tube, so that the output potential of the transmitter changes, brings about measurement error, and the dirt on the electrode reaches a certain degree. Thickness may cause the meter to fail to measure.
(5) Fouling or abrasion of the water supply pipe to change the inner diameter size will affect the original flow rate value and cause measurement error. For example, if the diameter of a 100mm diameter meter changes by 1mm, it will bring about 2% additional error.
(6) The transmitter's measurement signal is a very small millivolt potential signal. In addition to the flow signal, it also contains some signals that are not related to the flow rate, 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. Should improve the performance of the flow converter, it is best to use a microprocessor-type converter, use it to control the excitation voltage, according to the nature of the fluid to be selected excitation method and frequency, you can exclude the in-phase interference and orthogonal interference. However, the improved meter structure is complex and the cost is high.
(7) Higher prices
Application Overview:
Electromagnetic flow meters have a wide range of applications. Large-diameter meters are used in water supply and drainage projects; medium and small diameters are often used in demanding or unpredictable applications, such as the control of cooling water in blast furnace tuyere in the iron and steel industry, pulp and black liquor in the paper industry, and chemical industry Strong corrosive fluid, non-ferrous metallurgical industry pulp; small diameter, small diameter is often used in the pharmaceutical industry, food industry, biochemical and other health requirements. Since EMF entered industrial applications from the early 1950s, the use of the field has been expanding. Since the late 1980s, it has accounted for 16% to 20% of the sales amount of flow meters in various countries. China's rapid development in recent years, 1994 sales estimated at 6500 to 7500 units. China has produced ENF with a maximum diameter of 2~6m, and has a real-life calibration capability of 3m.
9 ultrasonic flowmeter
   
   
   
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Ultrasonic flowmeters are based on the geometrical principle of the speed at which ultrasonic waves propagate in a flowing medium equal to the mean flow velocity of the measured medium and the speed of the sound waves themselves. It is also measured flow rate to reflect the size of the flow. Ultrasonic flowmeters appeared in the 70s, but because they can be made into non-contact type, and can be measured in conjunction with ultrasonic water level meter opening flow measurement, the fluid does not produce disturbance and resistance, so very happy. Foshan Kobo Lighting CO.,LTD. , https://www.lightsattack.com
Ultrasonic flowmeter according to the principle of measurement can be divided into time difference and Doppler
The time-difference ultrasonic flowmeter manufactured by using the time-difference principle has received extensive attention and use in recent years, and is an ultrasonic flowmeter that is currently used most frequently by enterprises and institutions.
Ultrasonic Doppler flowmeters manufactured using the Doppler effect are used to measure the medium with a certain amount of suspended particles or bubbles, and their use has certain limitations, but it solves the problem that time-lapse ultrasonic flowmeters can only measure single clear fluids. It is also considered as an ideal instrument for non-contact measurement of two-phase flow.
advantage:
(1) Ultrasonic flowmeter is a non-contact measuring instrument, which can be used to measure fluid flow and large diameter flow which are difficult to contact and difficult to observe. It does not change the flow state of the fluid, does not generate pressure loss, and is easy to install.
(2) The flow of highly corrosive and non-conductive media can be measured.
(3) Ultrasonic flowmeter has a large measuring range, ranging from 20mm to 5m in diameter.
(4) Ultrasonic flow meters can measure various liquid and wastewater flows.
(5) The volumetric flow rate measured by the ultrasonic flowmeter is not affected by the thermophysical parameters such as the temperature, pressure, viscosity, and density of the measured fluid. Can be made in both fixed and portable forms.
Disadvantages:
(1) Ultrasonic flowmeters do not have a high temperature measurement range and generally only measure fluids with temperatures below 200°C.
(2) Poor anti-interference ability. It is susceptible to interference from ultrasonic noises such as air bubbles, scaling, pumps, and other sound sources, affecting the 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 of installation will bring greater error to flow measurement.
(5) The fouling of the measurement pipeline will seriously affect the measurement accuracy, bring about significant measurement error, and even when the instrument is severe, no flow is displayed.
(6) The reliability and precision grades are not high (typically about 1.5 to 2.5 grades), and the repeatability is poor.
(7) Short service life (General accuracy can only be guaranteed for one year).
(8) Ultrasonic flow meters determine the volumetric flow rate by measuring the fluid velocity. The mass flow rate of the liquid should be measured. The mass flow rate measured by the instrument is obtained by multiplying the volume flow rate by the artificially set density. When the fluid temperature changes, The density of the fluid is variable. Artificially setting the density value does not guarantee the accuracy of the mass flow. The fluid density can only be measured at the same time as the fluid velocity is measured, so that the true mass flow value can be obtained through calculation.
Application Overview:
The transit time method is applied to clean, single-phase liquids and gases. Typical applications include factory effluents,: Strange liquids, LNG, etc.; gas applications have good experience in the field of high pressure natural gas;
The Doppler method is suitable for use in biphasic fluids with relatively low levels of out-of-phase fluids, such as untreated sewage, factory discharge fluids, and dirty process fluids; it is usually not suitable for very clean fluids.
10 mass flow meters
Because the volume of the fluid is affected by parameters such as temperature, pressure, etc., the volume of the flow is used to indicate the flow rate of the media. In the case of continuous changes in the media parameters, it is often difficult to achieve this requirement, resulting in distortion of the instrument display value. Therefore, mass flow meters have been widely applied and valued. Mass flow meter is divided into direct and indirect two. The direct mass flow meter uses the principle directly related to the mass flow to measure. At present, mass flow meters such as calorimetric, angular momentum, vibratory gyro, Magnus effect, and Coriolis force are commonly used. An indirect mass flow meter uses a density meter and a volumetric flow rate to obtain a mass flow.
In modern industrial production, the operating parameters such as temperature, pressure, etc. of the working fluid are continuously increasing. In the case of high temperature and high pressure, due to the reasons of material and structure, the application of direct mass flowmeter has encountered difficulties and indirect quality. Flowmeters are often not practical because they are limited by the range of application of humidity and pressure. Therefore, temperature and pressure compensated mass flow meters are widely used in industrial production. It can be regarded as an indirect mass flowmeter instead of a densitometer. Instead, it uses the relationship between temperature, pressure, and density. It uses the temperature and pressure signals to calculate the density signal as a function, which is multiplied by the volumetric flow rate. Mass Flow. At present, temperature and pressure compensation mass flowmeters have been put into practical use. However, when the measured medium parameters vary widely or rapidly, correct compensation will be difficult or impossible. Therefore, further study of the applicable mass flow in actual production is made. Meters and densitometers are still a topic.
11 throttling flowmeter
A throttling device is installed on the gas flow pipe. An orifice plate is arranged in the gas flow channel. A hole is formed in the center and the hole diameter is smaller than the inner diameter of the pipe. The gas flows forward in a stable manner in front of the orifice plate, and the gas flows through the orifice plate. The smaller the hole diameter and the smaller the cross-sectional area, the more the steady flow state is disrupted, the flow rate will change, the speed will increase, and the static pressure of the gas will decrease. Therefore, the pressure drop will occur before and after the orifice plate, that is, the differential pressure Where the pressure is large, the pressure through the orifice plate is small where the small part). The magnitude of the differential pressure and the gas flow have a definite numerical relationship, that is, when the flow rate is large, the differential pressure is large, the flow rate is small, and the differential pressure is small. The flow is proportional to the square root of the differential pressure. The throttling flow meter is a meter that calculates the flow rate based on the differential pressure generated by the flow detection element installed in the pipeline, the known fluid condition, and the geometric dimensions of the detection element and the pipeline.
Features:
Throttle flowmeter is a typical differential pressure flowmeter. It is the most commonly used flow meter used to measure gas, liquid and vapor flow in industrial production. According to the survey statistics, flowmeters used in industrial production systems such as steelworks and oil refineries are around (70-80)%. In the entire field of industrial production, throttling flowmeters also account for more than half of the total number of flow meters. The throttling flow meter is so widely used, mainly because it has two outstanding advantages:
Simple structure, easy installation, reliable work, low cost, and a certain degree of accuracy. Can meet the needs of engineering measurement.
Has a long history of use, there are a wealth of reliable experimental data, design and processing has been standardized. As long as the throttling flowmeter is designed and processed according to the standard, no actual calibration is required, and flow measurement can be performed within the known uncertainty range.
Especially the second advantage makes the throttling flow meter very convenient in manufacturing and use. Because of a flow meter, especially for flow measurement of large flow, will encounter a variety of difficulties in the timing of the test.
12 nozzle flowmeter
   
　　
Waist wheel flowmeter, also known as the Roots flowmeter, is characterized by: a metering chamber in the meter body, one or two pairs of waist wheels that can rotate tangentially in the metering chamber. A pair of transmission gears are coaxially mounted on the outer surface of the flow meter housing with the two search wheels, and they mesh with each other so that the two waist wheels can be linked with each other. Waist wheel flow meter can be used for flow measurement of various cleaning liquids, especially for oil metering, and can also be used as a flow meter for measuring gas. It has the highest accuracy, up to 0.1-0.5.
Features:
Waist wheel flowmeter has novel design and beautiful appearance. With light weight, high precision, easy installation and use. It is one of the typical products of positive displacement flowmeters. Its main disadvantages are: bulky, bulky, large pressure loss, large vibration during operation, etc. The use of two pairs of waist wheel structures that form a mutual angle of 45 degrees can greatly reduce the vibration noise during operation.
16 Venturi flowmeter
   
The new generation of differential pressure flow measurement instruments, the basic measurement principle is based on the law of conservation of energy - the Bernoulli equation and the flow continuity equation based flow measurement method. The inner venturi tube consists of a circular measuring tube and a special type core body which is placed in the measuring tube and coaxial with the measuring tube. The radially outer surface of the special core body has a similar geometric shape to the inner surface of the classic venturi tube, and forms a different-diameter annular over-flow gap between the inner surface of the measuring tube and the inner surface of the measuring tube. The throttling process of the fluid flowing through the inner venturi is basically similar to the throttling process of the fluid flowing through the classic venturi tube and the annular orifice plate. The structural characteristics of the inner venturi tube do not have the problem of sharp edge abrasion and accumulation of the orifice plate throttling element during use, and can also have different gradients in the velocity distribution of the fluid in the tube before throttling and various possible existences. The non-axisymmetric velocity profile allows efficient flow adjustment (rectification) to achieve highly accurate and highly stable flow measurements.
Features:
Advantages: If it can be manufactured exactly according to the ASME standard, the measurement accuracy can also reach 0.5%, but the domestic Venturi is difficult to guarantee due to its manufacturing technology problems, and the domestically-qualified Kaifeng Instrument Factory with strong technical force can only guarantee 4 % Measurement Accuracy For the operation condition of ultra-supercritical power generation, the use of a pressure equalizing ring at the throat at high temperatures and pressures is a very dangerous step. If a pressure equalizing ring is not used, ASNE ISO5167 standard is not met and the measurement accuracy is There is no guarantee that this is a contradiction in the production of high-pressure classic Venturi.
Disadvantages:
The same material as the throat and the inlet/outlet, the erosion and wear of the fluid on the throat is severe, and the long-term measurement accuracy cannot be guaranteed. The length of the structure must be manufactured in accordance with ISO-5167, otherwise the required accuracy will not be achieved. Due to the stringent structural provisions of the classic Venturi in ISO-5167, the maximum/minimum flow ratio of its flow measurement range is very small, generally 3 – Between 5, it is difficult to meet the flow rate measurement with a large change in flow rate.
17 thermal mass flow meter (differential temperature difference TMF)
advantage:
(1) Ball valve installation, easy installation and removal. And can be installed with pressure.
(2) Direct measurement of mass flow based on King's law. The measured value is not affected by pressure and temperature.
(3) rapid response.
(4) Large measuring range, pipeline-type installation can measure the flow of 8.8mm pipeline, the maximum can be measured to 30''
(5) Plug-in type flow meters, one flow meter can be used to measure a variety of pipe diameters.
Disadvantages:
(1) The accuracy is not as good as other types of flowmeters, typically 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.
18 Coriolis Mass Flow Meter (CMF)
   
Coriolis mass flowmeter (hereinafter referred to as CMF) is a direct type mass flow meter made by using the Coriolis force principle which is proportional to the mass flow when a fluid flows in a vibrating tube.
The application of China's CMF started relatively late. In recent years, several manufacturing plants (such as Shanghai Zhengxi Technology) have developed their own supply markets; there are several manufacturing plants that form joint ventures or quote foreign technology to produce serial meters.
The foreign CMF has developed more than 30 series. The development of each series is focused on the technical aspects: design and innovation of the structure of the flow detection and measurement tube; improving the stability and accuracy of the instrument zero point; increasing the deflection of the measuring tube and increasing the sensitivity; improving the stress of the measuring tube Distribution, reduce fatigue damage, strengthen anti-vibration interference capabilities.
19 open channel flow meter
Different from the previous ones, it is a flow meter that measures the natural flow of a free surface in a non-full tubular open channel.
Water channels that are not full-pipelined are called open channels, and the flow of water in open channels is called an open channel flowmeter.
In addition to circular flow meters, there are U-shaped, trapezoidal, rectangular and other shapes.
The open channel flowmeter applies all the urban water supply diversion canals; the power plant diversion and drainage channels, the sewage treatment inflow and discharge canals; the industrial and mining enterprises water discharge and irrigation works and irrigation channels.有人估计1995å°,约å æµé‡ä»ªè¡¨æ•´ä½“çš„1.6%,ä½†æ˜¯å›½å†…åº”ç”¨å°šæ— ä¼°è®¡æ•°æ®ã€‚
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