Vortex street flowmeter principle
Establishes the triangle columnar order whirlpool in the fluid to have the body, has the body both sides from the whirlpool to produce alternately has the rule whirlpool, this kind of whirlpool is called the Carmen whirlpool, if the figure to the right shows, turns on lathe the vortex street to have the body downstream in the whirlpool to arrange asymmetrically.
Supposes the whirlpool the occurrence frequency is f, was measured that the medium mean velocity of stream is, the whirlpool has the body to welcome the flow surface width is d, shows the body latus rectum is D, then obtains the following relationship:

　f=SrU1/d=SrU/md 　　　　　　　　　　　　　　　　　　　　(1)
In the formula U1--The whirlpool has the body both sides mean velocity of stream, m/s;
　　　　 Sr--Strouhal number;
　　　　 m--Of the whirlpool has ratio of the body both sides arch area and the pipeline cross-section area
　　　　　　　　

　In the pipeline rate of volume flow qv is
　　　　　　　　　　　　 qv=πD2U/4=πD2mdf/4Sr 　　　　　　　　　　　　　　　　(2)
　　　　　　　　　　　　 K=f/qv= [πD2md/4Sr] - 1 　　　　　　　　　　　　　　　　 (3)
In the formula K--Flowmeter's scaling factor, the pulse counts /m3 (P/m3).
　　 K besides has the body, pipeline's geometry size with the whirlpool related, but also concerns with the Strouhal number. The Strouhal number is the zero dimension parameter, it has the build shape and the Reynolds number with the whirlpool related, shown in Figure 2 for the circle columnar whirlpool has body's Strouhal number and the pipeline Reynolds number relational graph. The figure shows, in ReD=2×104~7×106 the scope, Sr may regard as the constant, this is the measuring appliance normal work scope. When survey gas flow amount, the VSF current capacity formula is

 

　　　　　　　　　　 　　　　　　　　　　　　　　　　 (4)

Figure 2 Strouhal number and Reynolds number relations curve

In the formula qVn, qV--Respectively is under the standard state (0oC or 20oC,101.325kPa) and under the operating mode rate of volume flow, m3/h; 
　　 Pn, P--Respectively is under the standard state and the operating mode absolute pressure, Pa;
　　 Tn, T--Respectively is under the standard state and the operating mode thermodynamic temperature, K;
　　 Zn, Z--Respectively be under standard state under and operating mode gas loading coefficient. 
　　 Is obvious by the above equation, the VSF output's pulse frequency signal not the fluid nature and the component change's influence, namely the scaling factor only has in certain Reynolds number scope with the whirlpool the body and pipeline's shape size and so on concerns. But must examine the mass flow as the flowmeter in the mass balance and in the energy measurement, by now flowmeter's output signal should simultaneously monitor the rate of volume flow and the fluid density, the fluid nature and the component has the immediate influence to the flow measurement.

　　The vortex street flowmeter is carries on the solid surrounding boundary rate of fluid flow survey based on the Carmen whirlpool principle the new flowmeter. Because it has the good medium adaptiveness, does not need the temperature pressure compensation then direct measurement steam, the air, the gas, the water, the liquid operating mode rate of volume flow, provides the temperature, the pressure transmitter to be possible the surveyor's beacon situation rate of volume flow and the mass flow, is the throttle type flowmeter's ideal substitution product.
　　 In order to enhance the vortex street flowmeter thermostable and the vibration-proof mobility energy, Our company recently developed the SDLU advanced version vortex street flow sensor, because its unique structure and the selection cause this sensor to be possible in the high temperature (350℃), the strong vibration (≤1g) under the bad operating mode uses.
　　 In the practical application, often the maximum current capacity far is lower than measuring appliance's on limiting value, along with the load change, the minimum current capacity often will be lower than measuring appliance's lower limiting value, the measuring appliance works by no means in its best work section, to solve this problem, usually will use in the survey place reducing enhancement survey place speed of flow, and will select compares small caliber the measuring appliance to favor measuring appliance's survey, but this kind will change the diameter way must has the length between the reducing pipe and the measuring appliance be above the 15D straight length of pipe carries on the rectification, will cause the processing, the installment not to be convenient. Our company develops the longitudinal section shape changes the diameter rectifier for circular arc LGZ, has the rectification, to enhance the speed of flow and the change speed of flow distribution multiple actions, its structure size is small, is only the craft bore of pipe 1/3, makes a body with the vortex street flowmeter, not only does not need seperately to attach section of straight lengths of pipe, but may also reduce to the craft tube straight length of pipe request, the installment is convenient.

For the easy to operate, battery power supply's this locality demonstrated that the vortex street flowmeter uses the micro power loss high technology and new technology, uses the lithium battery power supply to be possible to move uninterruptedly above for one year, has saved the electric cable and display instrument's purchase fabricating cost, may demonstrate the transient flow, the integrated flux and so on. A temperature compensation build vortex street flowmeter also has the temperature sensor, may the direct measurement saturated steam temperature and calculates the pressure, thus demonstrates the saturated steam the mass flow. Thermobaric compensates a build to have the temperature, the pressure transmitter, uses in the gas flow amount survey being possible the direct measurement gas medium temperature and the pressure, thus demonstration gas sign situation rate of volume flow.
◆ survey medium: Gas, liquid, vapor
◆ the caliber specification flange card installs the type caliber to choose 25,32,50,80,100
◆ the flange connection type caliber chooses 100,150,200
◆ flow measurement scope normal survey speed of flow scope Reynolds number 1.5×104~4×106; Gas 5~50m/s; Liquid 0.5~7m/s
The normal survey current capacity scope liquid, the gas flow amount measuring range see Table 2; The steam flow scope see Table 3
◆ measuring accuracy 1.0 levels of 1.5 levels
◆ is measured the 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 dutyfactor approximately 50%, the transmitting range is 100m
◆ pulse current far signalling number 4~20 mA, the transmitting range is 1000m
◆ measuring appliance use ambient temperature: - 25℃~+55℃ humidity: 5~90% RH50℃
◆ material quality stainless steel, aluminum alloy
◆ power source DC24V or lithium battery 3.6V
◆ explosion-proof rank this peaceful iaIIbT3-T6
Protection rank IP65

Vortex street flowmeter product shaping