Published on：2014-12-29 8:45:35 Hits：
Measurement of fluid flow meter or flow meter collectively referred to as tables. Meter is one of the important industrial measurement instrumentation. With the development of industrial production for the accuracy and range of flow measurement have become increasingly demanding, flow measurement technology advances. In order to adapt to a variety of purposes, all types of flowmeters have been published. Flowmeter has been put into use has more than 100 kinds. From a different perspective, flowmeters have different classification methods. There are two commonly used classification methods, one meter by measuring principle be categorized using: Second flowmeter according to the principles of the classification structure.
First, according to the measuring principle classification
(1) mechanical principles: the principle of belonging to such instruments have the use of Bernoulli's theorem of differential pressure, rotor; use the momentum theorem of impulse type, movable tube; the use of direct mass formula of Newton's second law; the use of fluid momentum principle target type; the use of angular momentum theorem turbo; using fluid oscillation principle of vortex, vortex-type; the use of total static pressure difference between the pitot tube and the displacement and weir trough and so on.
(2) electrical principles: principles for such instruments have electromagnetic, differential capacitive, inductive, resistive strain and so on.
(3) acoustic principles: the use of acoustic principle has ultrasonic flow measurement. Acoustic formula (shock) and other.
(4) thermal principle: the principle of thermal flow measurement caloric formula, the amount of thermal direct and indirect calorimetry type and so on.
(5) of optics: Laser, photoelectric and other instruments that belong to this principle.
(6) The physical principle: magnetic resonance-type nuclear radiation type, and so belongs to such principles of the instrument.
(7) other principles: the principle marked (tracer principle, the principle of nuclear magnetic resonance), and other relevant principles.
Second, according to the principle of the meter structure classification
According to the actual conditions of the meter products, according to the principle structure flowmeter can be broadly grouped into the following types:
1. Volumetric flowmeter
Volumetric flow meter is equivalent to a standard volume of the container, which after another to measure the flow of the medium. The greater the flow, the more the number of metrics, the higher the frequency of the output. Volumetric flowmeter principle is relatively simple, suitable for measuring high viscosity, low Reynolds number fluid. According to the rotator different shapes, current products division: suitable for measuring liquid flow oval gear flow meter, Roots flowmeter (Roots meter), and the blade rotary piston flowmeter; suitable for measuring gas flow servo volumetric flow meter, film style and turn simple flowmeter.
2. Paddlewheel Flowmeter
Working principle of the impeller is an impeller type flow meter placed in the fluid to be measured, while the rotation by the impact of fluid flow, the speed of rotation of the impeller to reflect the size of the flow. Typical impeller and turbine flowmeter is water meter meter, its structure can be mechanical or electrical drive output type pulse output type. Meter accuracy is generally lower mechanical transmission output error of about ± 2%, but the simple structure, low cost, the country has been mass production, and standardized, universal and serialization. A high accuracy turbine flow meter output electrical pulse signal, typically an error of 0.5% ± 0.2%.
3. Differential pressure flowmeter (variable drop flowmeter)
Differential pressure flowmeter by a device and a secondary device component. Flow measuring means, said first element, which is installed in the pipeline fluid to be measured, generates flow (velocity) is proportional to the pressure difference, the flow rate for the secondary display device. Secondary device, said display instruments. It receives the measurement of differential pressure signal generating element, and converts it to the corresponding flow rate display. A differential pressure flow meter device often throttling device or dynamic pressure measurement device (pitot tube, the average rate, etc.). Secondary device with a flow rate of a variety of mechanical, electronic, modular differential pressure gauge indicator. Pressure sensor differential pressure gauge more elastic elements. Due to the square root of the differential pressure and flow relationship was, it is equipped with a flow meter showed that the square root system, so that the flow scale linear. Most instruments also have flow totalizer device to display the cumulative flow for economic accounting. This use of differential pressure flow measurement method has a long history, more mature countries in the world are generally used in more important occasions, accounting for 70 percent of various flow measurement. Main steam power plants, water supply and condensate flow measurement, etc. are using this meter.
4. Variable area flowmeter (such as drop flowmeter)
On the big small conical flow path float by force of fluid flowing bottom-up moves. When this force and float "Show weight" (minus the weight of the float itself, it suffered buoyancy fluid) equilibrium, ie stationary child prisoners. Static float height can be used as a measure of the flow size. Due to the cross-sectional area of the flow through the meter float varies with different heights, and the pressure does not move up and down when the float stable part of the difference is equal, so the variable area flowmeter, said flowmeter or equal drop flowmeter. A typical instrument of the flowmeter rotor (float) meter.
5. Momentum flowmeter
Use to measure the momentum of the fluid to reflect the size of the flow meter, said momentum flowmeter. Since the square of the density of the fluid flow and momentum P and the velocity v of the fluid, i.e., pv 2, when the through-flow cross-section is determined, v is proportional to the volume flow rate Q, so that p Q 2. Set scale factor is A, then Q = A Thus, the measured P, to reflect the flow Q. This type of flow meter, mostly using the detection element to convert the like momentum pressure, displacement or force, then measuring flow. This is a typical target type flowmeter instrument and rotating wing plate flowmeter.
6. Impulse type flowmeter
Use impulse theorem measure flow meter called impulse flow meter used for measuring the flow of granular solid medium is also used to measure the flow of mud, crystalline and liquid abrasives like. Flow measurement range from a few kilograms to nearly ten thousand tons per hour. A typical instrument is the horizontal component of the impulse type flowmeter, the measurement principle is that when measured media free fall from a height h to have a tilt angle detection plate produces a momentum, the level of force proportional to the mass flow rate of the momentum of the horse, so measuring the horizontal component to reflect the size of the mass flow. Press the signal (nine) of the detection method, this type of sub-meter displacement detection type and direct-type dynamometer.
7. Electromagnetic Flowmeter
Electromagnetic flowmeter is applied conductor in a magnetic field induced electromotive force movement, but also induced electromotive force proportional to the size and flow rate, by measuring the electromotive force to reflect the principles of pipeline flow made of. The measurement accuracy and sensitivity are higher. More water to flow in the industry, pulp and other media measurement. The maximum diameter can be measured up to 2m, and the pressure loss is minimal. However, a low conductivity medium, such as gas, steam, etc. can not be applied.
Higher cost of electromagnetic flowmeters, magnetic interference and the signal vulnerable to outside influence has been widely used in industrial pipe flow measurement. To this end, the product continues to improve and update to the microcomputer development.
8. Ultrasonic flowmeter
Ultrasonic flowmeter is based on ultrasonic wave propagation in the medium flow rate is equal to the principles of geometry and the average velocity and acoustic velocity measured medium itself and design. It is also to reflect the flow velocity from the measured size. Ultrasonic flowmeter in the 1970s, although it appears, but because it can be made non-contact type, and can be linked with an opening in the ultrasonic flow measurement water level, without creating turbulence and fluid resistance, so very popular, is a very there meter promising.
Manufactured using ultrasonic Doppler effect Doppler flowmeter widespread attention in recent years, are considered non-contact measurement of two-phase flow of the ideal instrument.
9. Oscillating fluid flow meter
Oscillating fluid flow meter is the use of fluid flow will oscillate under certain conditions of the flow channel, and the frequency and velocity is proportional to the oscillation of the principles of design. When the through-flow cross-section is constant, proportional to the flow velocity and volume guide. Therefore, measuring the oscillation frequency can be measured flow. This meter is developed in the 1970s and developed. Because it combines the advantages of no moving parts and digital pulse output promising. Typical products are currently vortex flowmeter, Swirlmeter.
10. Mass flowmeter
Due to the volume of fluid temperature, pressure and other parameters by using the given parameters required volume flow represents the flow of media size. In the case of medium parameters changing, often difficult to meet this requirement, the value of the distortion caused by the instrument display. Therefore, mass flowmeter to be widely used and valued. Direct mass flow meter and indirect sub-two. Direct mass flow meters and mass flow using the principle of direct relevance to the measurement, the current commonly used calorimetric angular momentum type vibration gyro, Magnus-effect and Coriolis mass flowmeter type, etc. Indirect mass flowmeters and density meter is obtained by multiplying the volume flow mass flow directly.
In modern industrial production, the flow of the working fluid temperature, pressure and other operating parameters continue to improve, in the case of high temperature and pressure, due to the material and structural aspects of the application of direct mass flowmeter difficulties, while indirect quality Because of the density meter meter limit humidity and pressure by the scope, often not a good practice. Thus, widely used in industrial production is temperature and pressure compensated mass flow meter. It could be seen as an indirect mass flowmeter, is not equipped with a densitometer, but to use the relationship between temperature, pressure and density between the temperature, pressure, density signal by the function operation signal obtained by multiplying the volume flow mass flow. Current temperature, pressure compensated mass flow Although practical, but a large range of parameters measured medium or very quickly when properly compensated would be difficult or impossible, and therefore further studies in the actual production of the mass flow rate applicable density meter or meter and a subject.
Chen meter above common structural principles than many meter various structures, such as for a variety of weir flow meter, flow meters open channel flow measurement trough; suitable for measuring the flow of large diameter insertion flowmeter; measuring layer laminar flow flow meter; flowmeter is suitable for two-phase flow correlation measurement; and laser method, nuclear magnetic resonance spectroscopy and multiple meter tracer method, dilution method to measure the flow and so on. With the development and practical application of science and technology needs, the new type of meter meter will continue to emerge will be more complete.
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