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

1. Volumetric flow meters

Volumetric flowmeter is equivalent to a standard volume container, which successively measures the flowing medium. The larger the flow rate, the more measurements, the higher the frequency of the output. Volumetric flowmeter principle is relatively simple, suitable for measuring high viscosity, low Reynolds number of fluid. According to the shape of the rotary body is different, the current production of products: suitable for measuring the flow of liquid elliptic gear flowmeter, girdle wheel flowmeter (Roots flowmeter), rotary piston and scraper type flowmeter; suitable for measuring the flow of gas servo type volumetric flowmeter, skin film type and the turn of the simple flowmeter and so on.

2. Impeller flow meters

The working principle of impeller flowmeter is to place the impeller in the measured fluid, impacted by the fluid flow and rotate to reflect the size of the flow rate by the speed of the impeller rotation. Typical impeller flowmeter is a water meter and turbine flowmeter, its structure can be mechanical transmission output type or electrical pulse output type. General mechanical transmission output of the water meter accuracy is low, the error is about ± 2%, but the structure is simple, low cost, the domestic has been mass production, and standardization, generalization and serialization. Electrical pulse signal output of the turbine flowmeter accuracy is higher, the general error of ± 0.2% ~ 0.5%.

3. Differential pressure flowmeters (variable pressure drop flowmeters)

Differential pressure flowmeter consists of a primary device and a secondary device. Primary device called flow measurement element, which is installed in the measured fluid pipeline, resulting in a pressure difference proportional to the flow rate (flow rate) for the secondary device for flow display. Secondary device called display meter. It receives the differential pressure signal generated by the measuring element and converts it to the corresponding flow rate for display. Differential pressure flowmeter primary device is often a throttling device or dynamic pressure measurement device (Pitot tube, homogeneous tube, etc.). Secondary device for a variety of mechanical, electronic, combined differential pressure meter with flow display instrumentation. Differential pressure sensitive components of the differential pressure gauge are mostly elastic components. As the differential pressure and flow rate is square root relationship, so the flow rate display instrumentation are equipped with a square device in order to linearize the flow rate scale. Most of the instruments are also equipped with flow accumulation device to display the cumulative flow for economic accounting. This method of measuring flow using differential pressure has a long history, more mature, countries around the world are generally used in more important occasions, accounting for about 70% of the various flow measurement methods. Power plant main steam, feedwater, condensate and other flow measurement are used in this meter. The current production of products: orifice plate flowmeter, wedge-shaped flowmeter, venturi flowmeter, average Pitot tube.

4. Variable area flow meters (equal pressure drop flow meters)

A float placed in a conical flow channel with a large top and a small bottom is moved by the force of the fluid flowing from the bottom up. When this force is balanced by the float's "display weight" (the weight of the float itself minus the buoyant force of the fluid it is subjected to), the captive comes to rest. The height of the float at rest can be used as a measure of the flow rate. Due to the flow meter of the cross-sectional area of the flow with the height of the float is different, while the float is stable and immobile when the pressure difference between the upper and lower parts of the equal, so the type of flowmeter is called variable area flowmeter or pressure drop type flowmeter. Typical instruments of this type of flowmeter are rotor (float) flowmeter.

5. Momentum flowmeters

The use of measuring the momentum of the fluid to reflect the size of the flow meter called momentum flow meter. As the momentum of the flowing fluid P and the density of the fluid and the flow rate of v is proportional to the square, that is, p v2, when the cross-section of the through-flow determined, v and volumetric flow rate Q is proportional to, so p Q2. proportionality coefficient for A, then Q = A Therefore, measured P, can reflect the flow rate of Q. This type of flowmeter, most of the use of the detection element of the momentum is converted to pressure, displacement, or force, and then measure the flow rate. Typical instruments of this type of flowmeter are target and rotating wing plate type flowmeter.

6. Impulse flowmeters

Using the impulse theorem to measure the flow rate of the flowmeter called impulse flowmeter, mostly used to measure the flow rate of granular solid media, but also used to measure the flow rate of mud, crystalline liquids and abrasive materials. Flow measurement range from a few kilograms per hour to nearly 10,000 tons. Typical instrumentation is the level of impulse impulse flowmeter, its measurement principle is when the measured medium from a certain height h free fall to have an angle of inclination of the detection of the plate to produce an impulse, impulse of the level of the force of the mass flow rate is proportional to the mass flow rate, so the measurement of the level of the force of the mass flow rate can be reflected in the magnitude of this level of the force. According to the signal (ix) of the detection method, the type of flowmeter is divided into displacement detection type and direct force measurement type.

7. Electromagnetic flowmeters

Electromagnetic flowmeter is the application of conductive body movement in the magnetic field generates induced electromotive force, and induced electromotive force and flow size is proportional to the measured electromotive force to reflect the principle of pipeline flow and made. Its measurement accuracy and sensitivity are high. Industry is used to measure the flow of water, slurry and other media. The maximum diameter of the pipe can be measured up to 2m, and the pressure loss is very small. But the low conductivity of the medium, such as gas, steam, etc. can not be applied.

Electromagnetic flowmeter cost is high, and the signal is susceptible to external magnetic field interference, affecting the industrial pipe flow measurement in a wide range of applications. For this reason, the product is constantly improving and updating, to the development of microcomputerization.

8. Ultrasonic flowmeters

Ultrasonic flowmeter is based on ultrasonic propagation speed in the flow medium is equal to the average flow rate of the measured medium and the sound wave itself the speed of the geometric sum of the principle and design. It is also measured by the flow rate to reflect the size of the flow. Although ultrasonic flowmeter only appeared in the 70's, but because it can be made into a non-contact type, and can be linked with ultrasonic level meter for open flow measurement, the fluid and does not produce disturbance and resistance, so it is very popular, is a very promising flowmeter.

Classification of ultrasonic flowmeter: 1 multispectral ultrasonic flowmeter: transducer 1 transmits ultrasonic signals with a frequency of f1, after the pipeline liquid suspended particles or bubbles, the frequency shift occurs, with a frequency of f2 reflected back to the transducer 2, which is the multispectral will be, f2 and the difference between f1 that is, the difference between the multispectral frequency difference fd. Set the fluid flow rate is v, ultrasonic sound speed is c, multispectral shift fd is proportional to the fluid flow rate v. When the pipeline flow rate v. When the pipeline flow rate of ultrasonic flowmeter, fd is proportional to the fluid flow rate. When the pipeline conditions, transducer installation location, launch frequency, sound speed to determine later, c, f1, θ that is constant, fluid flow rate and spectral frequency shift is proportional to the measurement of the frequency shift can be obtained from the fluid flow rate, and then get the fluid flow rate. 2 time-difference ultrasonic flowmeter: time-difference ultrasonic flowmeter is the use of acoustic sound wave propagation and countercurrent propagation of the time difference between the fluid and fluid flow rate is proportional to this principle to measure the fluid flow rate. This principle is proportional to the fluid flow measurement.

9. Fluid Oscillation Flowmeters

Fluid oscillation flowmeter is the use of fluid flow in a particular channel conditions will produce oscillation, and the frequency of oscillation and flow rate proportional to the principle of design. When the cross-section of a certain cross-section, the flow rate is directly proportional to the volume of flow. Therefore, the measurement of the oscillation frequency can be measured flow. This kind of flow meter is the 70's development and development. Because it has no rotating parts and pulse digital output advantages, very promising. At present, the typical products are vortex flowmeter, vortex flowmeter.

10. Mass flowmeters

 As the volume of the fluid is affected by temperature, pressure and other parameters, the volume flow rate to indicate the flow rate of large hours need to give the parameters of the medium. In the case of changing media parameters, it is often difficult to meet this requirement, resulting in instrument display value distortion. Therefore, the mass flow meter has been widely used and attention. Mass flow meter is divided into direct and indirect type two kinds. Direct mass flow meter with the use of mass flow rate directly related to the principle of measurement, commonly used calorimetric, angular momentum, vibration gyroscope type, Magnus effect type and Coriolis force type of mass flow meter. Indirect mass flow meter is a density meter and volume flow rate directly multiplied by the mass flow rate.

There are also suitable for open channel flow measurement of a variety of weir flowmeter, slot flowmeter; suitable for large diameter flow measurement of insertion flowmeter; measurement of laminar flow flowmeter laminar flowmeter; suitable for two-phase flow measurement of correlation method flowmeter; as well as the laser method, nuclear magnetic resonance method of flowmeter and a variety of tracer, dilution method of measurement of the flow, etc.