Vortex air flow meter

Vortex air flow meter

Vortex flowmeter is researched and produced according to Karman vortex principle. It is mainly used for flow measurement of industrial pipeline medium fluids, such as gas, liquid, steam and other media. It is characterized by small pressure loss, large range and high accuracy. It is almost unaffected by fluid density, pressure, temperature, viscosity and other parameters when measuring volumetric flow under working conditions. There are no movable mechanical parts, so the reliability is high and the maintenance is small. The instrument parameters can be stable for a long time. Vortex flowmeter adopts piezoelectric stress sensor, which has high reliability and can work in the working temperature range of -20 ℃ ~ +250 ℃. It has analog standard signal and digital pulse signal output, which is easy to be used with digital systems such as computers. It is a relatively advanced and ideal measuring instrument.

Main tech data

◆ caliber specification flange snap on caliber selection 25,32,50,80,10
◆ the diameter of flange connection type is 100150200
◆ flow measurement range normal measurement flow rate range Reynolds number 1.5 × 104~4 × 106； Gas 5 ~ 50m/s; Liquid 0.5 ~ 7m/s
See Table 2 for the normal measurement flow range of liquid and gas flow; See Table 3 for steam flow range
◆ measurement accuracy level 1.0 level 1.5
◆ measured medium temperature: normal temperature – 25 ℃ ~ 100 ℃, high temperature – 25 ℃ ~ 150 ℃ -25 ℃ ~ 250 ℃
◆ output signal pulse voltage output signal high level 8 ~ 10V low level 0.7 ~ 1.3V
◆ the pulse duty cycle is about 50%, and the transmission distance is 100m
◆ pulse current remote transmission signal is 4 ~ 20 mA, and the transmission distance is 1000m
◆ ambient temperature of instrument: -25 ℃ ~ +55 ℃ humidity: 5 ~ 90% Rh50 ℃
◆ material: stainless steel, aluminum alloy
◆ power supply DC24V or lithium battery 3.6V
◆ explosion proof grade: intrinsically safe iaiibt3-t6, protection grade: IP65

◆ measuring medium: gas, liquid, vapor
◆ connection mode: flange snap on type, flange type, plug-in type

Working priciple of Vortex air flow meter

Vortex flowmeter uses the fluid oscillation principle to measure the flow. When the fluid passes through the vortex flow transmitter in the pipeline, two rows of vortices proportional to the flow rate are alternately generated up and down behind the vortex generator of the triangular column. The release frequency of the vortex is related to the average velocity of the fluid flowing through the vortex generator and the characteristic width of the vortex generator, which can be expressed by the following formula

If a triangular cylindrical vortex generator is set in the fluid, regular vortices are alternately generated from both sides of the vortex generator. This vortex is called Carmen vortex. As shown in the right figure, the vortices are arranged asymmetrically downstream of the vortex generator.
Vortex flowmeter is a volume flowmeter that measures the volume flow of gas, steam or liquid, the volume flow or mass flow of standard condition according to Karman vortex principle. It can be used as flow transmitter in automatic control system.

Major function
1. The temperature and pressure compensation function is also integrated in the table body, which can measure the standard volume flow or standard mass flow of fluid.
2. Fully intelligent and digital circuit design, which can automatically compensate the calculation of measured fluid density or standard condition volume.
3. The new digital filtering and correction functions make the flow measurement more accurate and reliable.
4. Battery powered type can work continuously for more than two years without external power supply.
5. The new dot matrix Chinese character LCD display is more convenient to use and operate.

Common faults
Common faults of vortex flowmeter IX. a DN50 vortex flowmeter, according to the instructions, its liquid flow range is 3-50m3 / h. The result of our calibration on the oil flow standard device is that 10-50 m3/h meets the accuracy requirements, but the accuracy below 10m3/h is unqualified. How should we evaluate this flowmeter?
In the specification of vortex flow juice, the flow range indicated is the flow range used for a specific reference medium, such as liquid, which generally refers to constant temperature water. When used in other media, the available flow range will vary with the viscosity and density of the media. Since the oil flow standard device uses diesel oil with higher viscosity and less density than water as the calibration medium, the lower limit flow of the flowmeter will generally be increased accordingly, narrowing the available flow range. Therefore, it is normal for vortex flowmeter to have poor performance in small flow calibration on oil flow calibration device. Therefore, it is not difficult to infer that if liquefied petroleum gas (this low viscosity medium) is used to calibrate vortex flow juice, the opposite result will be better than that of water.

1. The measurement range of vortex flowmeter is large, generally 10:1, but the lower limit of measurement is limited by many factors: re>10000 is the most basic condition for the operation of vortex flowmeter. In addition, it is also affected by the response signal generated by vortex, and the vortex frequency f is also small, which also makes signal processing difficult. The upper limit of measurement is the frequency response of the sensor and the frequency limit of the circuit. Therefore, the flow rate range must be calculated and calculated in the design, and the selection should be made according to the flow rate of the fluid. The environmental conditions on the use site are complex. In addition to paying attention to the environmental temperature, humidity, atmosphere and other conditions, electromagnetic interference should also be considered in the selection.

2. Vibration is also a major enemy of this kind of instrument. Therefore, attention should be paid to avoid mechanical vibration during use, especially the transverse vibration of the pipeline (vertical to the pipeline axis and vertical to the vortex generation body axis). This influence cannot be suppressed and eliminated in the structural design of the flowmeter. Because the vortex signal is also sensitive to the influence of the flow field, it is not suitable to choose when the length of the straight pipe section cannot ensure the necessary flow conditions for stabilizing the vortex. Even capacitor type and ultrasonic type with strong vibration resistance can not be ignored to ensure that the fluid is a fully developed unidirectional flow.

3. The medium temperature also has a great influence on the performance of vortex flowmeter. For example, the pressure stress vortex flowmeter cannot be used at 300 ° C for a long time, because its insulation impedance will drop sharply from 10-100m Ω at room temperature to 1-101 Ω, and the output signal will also become smaller, resulting in the deterioration of measurement characteristics. In the measurement system, the sensor and converter should be installed separately to avoid long-term high temperature affecting the reliability and service life of the instrument. Vortex flowmeter is a relatively new type of flowmeter, which is in the development stage and is not very mature. If it is improperly selected, its performance will not play well. Only after reasonable selection and correct installation, it is also necessary to carefully and regularly maintain in the process of use, constantly accumulate experience, and improve the predictability of system faults and the ability to judge and deal with problems, so as to achieve satisfactory results.