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:
Differential capacitor type,
Strain resistance type, etc.
c. Acoustic principle:
d. Thermal principles:
Indirect calorimetry and so on.
Main features of vortex flowmeter
Measuring medium: nominal diameter of liquid, gas and steam: DN15-DN300 (non-standard products can be customized according to user requirements) Temperature range: -40°C~350°C Pressure specification: PN1.6Mpa; PN2.5Mpa; PN4.0Mpa, Higher pressure specifications can be customized to a specific range: normal range 1:10 Extended range 1:15 Pressure loss factor: Cd ≤ 2.6 System measurement accuracy: liquid, gas indication ± 1%, steam indication ± 1.5% plug-in flow The measured value is ±2.5% of the supply voltage: sensor +12VDC, +24VDC (optional) transmitter +24VDC.
On-site display type The meter comes with 3.6 lithium battery output signal: sensor pulse frequency signal 0.1~3000Hz low level ≤1V high level ≥6V.
Transmitter two-wire 4~20mADC current signal for vibration acceleration: Piezoelectric ≤0.2g Ambient temperature: -40°C~55°C (non-explosion-proof place) -20°C~55°C (explosion-proof place) Ambient humidity: Relative Humidity 5~85% signal remote transmission distance: ≤500m signal line interface: internal thread M20×1.5 explosion-proof grade: iaIICT2-T5 protection grade: ordinary IP65 submersible IP68 instrument material: converter shell is made of aluminum alloy, the body part is adopted 1Cr18Ni9Ti can also be made of special materials according to user requirements.
The working principle of the impeller type flowmeter is that the impeller is placed in the fluid to be measured, and is rotated by the impact of the fluid flow, and the flow rate is reflected by the speed of the impeller rotation. Typical impeller flow meters are water meters and turbine flow meters, which may be of mechanical transmission output or electrical pulse output. Generally, the water meter output of the mechanical transmission has low accuracy and the error is about ±2%, but the structure is simple and the cost is low. The domestic production has been mass-produced, standardized, generalized and serialized. The accuracy of the turbine flowmeter for electrical pulse signal output is high, with a typical error of ±0.2% to 0.5%.
Differential pressure flowmeter (variable pressure drop flowmeter)
The differential pressure flowmeter consists of a primary device and a secondary device. The primary device is called a flow measuring element and is installed in the pipe of the fluid to be measured, generating a pressure difference proportional to the flow rate (flow rate) for the secondary device to display the flow rate. The secondary device is called a display instrument. It receives the differential pressure signal generated by the measuring component and converts it to the corresponding flow for display. The primary device of the differential pressure flow meter is often a throttling device or a dynamic pressure measuring device (piteron, constant velocity tube, etc.). The secondary device is equipped with various mechanical, electronic and combined differential pressure gauges with flow display instruments. The differential pressure sensitive components of the differential pressure gauge are mostly elastic components. Since the differential pressure and the flow rate are in a square root relationship, the flow display instrument is equipped with an open square device to linearize the flow scale. Most meters also have a flow accumulator to display cumulative flow for economic accounting. This method of measuring flow using differential pressure has a long history and is relatively mature. Generally, countries all over the world use it in more important occasions, accounting for about 70% of various flow measurement methods. The flow measurement of the main steam, feed water, condensate, etc. of the power plant is based on this meter.