2019/9/21 15:40:23

Instruments that measure fluid flow are collectively referred to as flow meters or flow meters. The flowmeter is one of the important instruments in industrial measurement. With the development of industrial production, the accuracy and range of flow measurement requirements are getting higher and higher, and the flow measurement technology is changing with each passing day. Various types of flow meters have been introduced to suit various applications. More than 100 flow meters have been put into use. From different perspectives, flow meters have different classification methods. There are two commonly used classification methods. One is to classify according to the measurement principle adopted by the flowmeter: the second is to classify according to the structural principle of the flowmeter.

Sort by measurement principle

a. Mechanical principle:

Instruments belonging to such principles have differential pressure type, rotor type using Bernoulli's theorem;

Impulse type using the momentum theorem, movable tube type;

Direct mass equation using Newton's second law;

a target using the principle of fluid momentum;

Turbine using the angular momentum theorem;

Vortex type using vortex principle of fluid oscillation;

Use the total static pressure difference of the pitot tube type as well as volumetric and sputum, trough and so on.

b. Electrical principle:

Electromagnetic,

Differential capacitor type,

Inductive,

Strain resistance type, etc.

c. Acoustic principle:

Ultrasonic.

d. Thermal principles:

Thermal type,

Direct calorimetry,

Indirect calorimetry and so on.

Vortex flowmeter verification detection method

Standard table method

The vortex flowmeter is used as a standard device in series with the flowmeter to be inspected, and can be verified by static method or dynamic method. By comparing the readings of the two flow meters, the error of the vortex flowmeter to be tested is obtained.

Standard table flow meter standard device features:

1. Standard table method is suitable for measuring various fluids (including liquids and gases), and also for liquids of various viscosities.

2. The indication value is checked. The flow meter used as the standard meter is installed in series with the flowmeter to be tested in the same closed pipeline system. Generally, there is no time measurement error.

3. As a standard table, the vortex flowmeter can be the same as or different from the flowmeter to be tested.

4. When the flow meter is verified by the standard meter method, the airflow or liquid flow can be not cut off, so it is suitable for online verification, and is also suitable for the measurement standard for the closed pipeline. 5, the standard table method is easy to achieve automation, sealed and safe, does not pollute the environment.

6. Small size, light weight, simple device structure, convenient operation, easy transportation and installation, and low cost.

7. Standard meter flowmeters have low accuracy and poor stability, and often need to be compared regularly or irregularly to monitor their metering performance. The standard table has a shorter verification period.

Variable area flowmeter (equal pressure drop flowmeter)

The float placed in the upper and lower small tapered flow passages is moved by the force of the fluid flowing from the bottom to the top. When this force is balanced with the "display weight" of the float (the weight of the float itself minus the buoyancy of the fluid it receives), the capture is stationary. The height at which the float is stationary can be used as a measure of the flow rate. Since the cross-sectional area of ??the flowmeter varies with the height of the float, and the pressure difference between the upper and lower parts is equal when the float is stationary, the flowmeter is called a variable area flowmeter or an equal pressure dropmeter. A typical instrument of this type of flow meter is a rotor (float) flow meter.

Momentum flowmeter

A flowmeter weighing flowmeter that uses the momentum of a measuring fluid to reflect the flow rate. Since the momentum P of the flowing fluid is proportional to the density of the fluid and the square of the flow velocity v, i.e., p v2 , when the flow cross section is determined, v is proportional to the volumetric flow rate Q, so p Q2 . Set the proportional coefficient to A, then Q=A. Therefore, P is measured to reflect the flow rate Q. In this type of flowmeter, most of the flowmeters are used to convert momentum into pressure, displacement or force, and then the flow rate is measured. Typical meters for such flow meters are target and rotary wing flow meters.