Measuring the flow of fluid flow meter or meter collectively referred to as the flow table. Flowmeter is an important industrial measurement of one of the instruments. With the development of industrial production, the flow measurement accuracy and scope of the increasingly demanding high flow measurement technology advances . In order to adapt to a variety of purposes, the various types of flowmeters have come out in succession. Has been put into use the flowmeter has more than 100 kinds. From a different point of view, flowmeters have different classification. Categories used two ways, first by a flow meter into the measurement principle of classification: the structure is based on principles of flowmeter classification.

һBy measuring principle Categories

(1)Mechanical principles: the principle of such instruments is the use Bernoulli's theorem Differential, the rotor; theorem using the momentum of impulse, movable-type of the use of Newton's Second Law of the quality of direct the use of the principle of fluid momentum Target-the use of angular momentum theorem turbine-the use of the vortex of fluid-oscillation theory, the vortex of the use of the total static pressure difference and the Pitot tube and the volume of Weir, trough, and so on.

(2)Electrical principles: the principle instrument for such a magnetic, differential capacitive, inductive, such as contingency resistance.

(3)Acoustic principle: The principle of acoustic measurement of a flow-ultrasound. Acoustic-(shock-).

(4)Thermal principle: The principle of thermal measurement of heat flow is directly of heat-,-, and other indirect calorimeter.

(5)Optical principles:-laser, optical, and so is the principle of such instruments.

(6)In the original principles of physics: NMR-and-such as nuclear radiation is the principle of such instruments.

(7)Other principles: marked principle (tracer principle, principle of nuclear magnetic resonance), and other relevant principles.

2Flowmeter structure according to principles of classification

According to the current flow meter product of the actual situation, according to the flow meter structure principle, can be broadly grouped into the following types:

1Volume Flowmeter

Volume flowmeter equivalent to a standard volume of containers, it continuously on the mobile medium to measure. Traffic is, the more the number of measurement, the higher the frequency output. Volume flowmeter the principle is relatively simple, suitable for measuring high-viscosity, low Reynolds number of fluid. According to Rotary different shape, the sub-products: suitable for measuring the flow of liquid flow meter oval gear, Roots Meter (Roots flowmeter), rotating the Pistons and scraper flowmeter; suitable for measuring the gas flow servo - Volume flowmeter, and membrane-type flowmeter, and so on to SR.

2Impeller Flowmeter

Impeller flowmeter the working principle is to place the measured fluid in the impeller, the fluid flow and the impact of rotation, the speed of rotation to impeller flow to reflect the size. Typical of the impeller and turbine flowmeter is metered flowmeter, its structure can be a mechanical or electrical pulse output output. General mechanical transmission output meter accuracy of the low error of about 2%, but the structure is simple, low cost, domestic production has been, and standardization, universal and serialization. Electrical pulse signal output of turbine flow meter high degree of accuracy, the general error of 0.2% 1 0.5%.

3Pressure-flow meter (variable pressure flowmeter)

Differential Flowmeter from a secondary device components and devices. A device that flow measurement devices, it installed in the tested fluid in the pipeline, with a flow (velocity) is proportional to the pressure difference for secondary devices flowʾ. Secondary display device that instrument. It measured components to receive the differential signal, and converting it to a corresponding flow display. Differential pressure flow meter is a device often cutting expenditure dynamic pressure of device or devices (Pitot tube, all-speed, etc.). Secondary devices for a variety of mechanical, electronic, or supported by the modular differential pressure flow meters show. Differential of Pressure-sensitive components for more flexible components. Pressure and flow was due to the square root, it shows that flow meters are equipped with a square device to enable the flow of the linear scale. Most instrument also has Flow Totalizer devices, to show the cumulative flow, so as to economic accounting. This use of differential pressure flow measurement method has a long history, more mature, countries around the world are generally used in the more important occasions, about the various ways of measuring flow 70 percent. The main steam power plants, water supply, water condensation, such as measuring the flow of all such meters.

4Variable area flowmeter (such as pressure-flow meter)

On the large flow of small, cone-shaped float in the bottom-up by the flow of the fluid and mobile force. When the float and force the "show weight" (minus the weight of its own float it suffered fluid buoyancy) equilibrium, the prisoners of that is static. Float a high degree of static size can be used as a measure of traffic. As flowmeter flow cross-sectional area with a high degree of Float vary, and the stability of fixed float when the pressure difference from top to bottom part of the same, so that changes of this type of flow meter area flowmeter, such as pressure or flow meter. The flowmeter is the typical instrument rotor (float) flowmeter.

5Momentum Flowmeter

Measuring the momentum of fluid flow to reflect the size of flowmeter that momentum flowmeter. Fluid flow due to the fluid momentum P and the density and velocity v proportional to the square, pv 2, when the flow cross-section determine when, v and the volume Q is directly proportional to flow, the p Q 2. A ratio coefficient of A, while Q = A Therefore, the measured P, to reflect the flow Q. This type of flowmeter, most detection devices to use the momentum into pressure, displacement or force, and then measuring flow. This flow meter is a typical instrument-and rotary-wing target plate flowmeter.

6Impulse Flowmeter

Impulse theorem using the flow meter flow measurement that impulse flowmeter, more used to measure the flow of granular solid medium, also used to test the mud, the crystallization of liquids and abrasive, and other traffic. Flow measurement range from a few kilograms per hour to nearly 10,000 tons. Instrumentation is a typical level of effort impulse-Meter, measuring principle, when measured from a certain height h media freedom to the whereabouts of a tilt angle of the impact of testing produce a board, the impact of the level of mass flow directly proportional to help Ma, the Measuring the level of effort to reflect the size of mass flow. The signal (9) testing, this type of displacement flowmeter-detection-and direct measurement of the type.

7Electromagnetic Flowmeter

Electromagnetic Flowmeter is the application of electrical conductors in the magnetic field generated in the movement sensors EMF, and the induction EMF also directly proportional to the size and flow through the pipeline to reflect EMF measurement of the flow and made the principle. Its accuracy and sensitivity are higher. Industry to measure more water, pulp and other media traffic. Can be measured maximum diameter of 2 m, and minimal pressure loss. However, the low rate of the conductive medium, such as gas, steam, and so can not be applied.

Electromagnetic Flowmeter higher cost, and vulnerability to external magnetic field signal interference, and affected the flow of industrial measurement of the extensive application. To this end, the continuous improvement of products in the update to computer development.

8Ultrasonic Flowmeter

Ultrasonic Flowmeter is based on ultrasound in mobile communication medium speed equivalent to the average velocity measured media and the speed of sound itself and the principles of geometric design. It is also measured by the flow rate to reflect the size of the flow. Ultrasonic Flowmeter Although only in the 1970s, but because it can be made of non-contact type, and with the water level gauge linked to openings ultrasonic flow measurement, the fluid does not generate disturbances and obstacles, so very popular, is a great development The future of the flowmeter.

Doppler effect created by using Doppler ultrasonic flowmeter been widespread concern in recent years, is considered a non-contact measurement of the ideal two-phase flow meters.

9Fluid oscillation Flowmeter

Oscillation fluid flow meter is used in a particular fluid flow, liquidity conditions will produce oscillations, and the oscillation frequency and velocity proportional to the principles of design. When a certain section flow, speed and volume of flow in direct proportion to lead. Therefore, the oscillation frequency measurements can be measured flow. Flowmeter this is the 1970s development and develop. Both because it contains no moving parts and pulse of the advantages of digital output, is very promising. At present the typical products vortex flowmeter, Swirlmeter.

10Mass Flowmeter

As the volume of fluid temperature, pressure and other parameters of the impact, said traffic volume of traffic using the size of the media to be given parameters. In the medium parameters changing circumstances, are often difficult to meet this requirement, and the value of the instrument showed that distortion. Therefore, the mass flow meter on a wide range of applications and get attention. Meter-quality direct-and indirect-two. Direct mass flowmeter with the use of mass flow directly related to the principle of measurement, there are now commonly used in thermal and angular momentum-and vibration-gyro, the Magnus effect-and-such as the quality of the Coriolis flowmeter. Indirect mass flowmeter is density of traffic volume and direct the flow of the quality of the product obtained.

In modern industrial production, the flow of the temperature, pressure and other operating parameters continue to improve, in high temperature and high pressure of circumstances, material and structural aspects of reasons, the direct application of mass flowmeter difficulties, and the indirect-quality Flowmeters because of the density of humidity and pressure on the scope of the restrictions, are often not good practical application. Therefore, in industrial production is widely used in temperature and pressure compensation mass flowmeter. May see it as a kind of indirect mass flowmeter, not with density of use, but use of temperature, pressure and density of the relationship between, with temperature, pressure signal for the function computing density signal, and the volume of traffic multiply and receive quality Flow. Current temperature and pressure compensation mass flowmeter, though useful, but when measured parameters of the medium or large very quickly, correctly compensation will be very difficult or impossible, so further study in the actual production of the applicable quality Flowmeters and density meter is still a subject.

Chen used the principle of the flowmeter structures than many of the flowmeter, as applicable to the various channel flow measurement weir flowmeter, slotted flowmeter; suitable for large-diameter measuring the flow plug-Meter measurement of Laminar flow of the traffic flow meter; suitable for two-phase flow measurements of the relevant law flowmeter, and laser, NMR flowmeter and a variety of tracer, such as dilution flow measurement. With the development of technology and practical application needs, the new flow meter will continue to emerge flowmeter type will be more complete.