Tiankang share the field application of vortex flowmeter

Under certain flow conditions, part of the fluid kinetic energy will be converted into fluid vibration. The vibration frequency has a definite proportional relationship with the flow rate (flow rate). The flowmeter operating on this principle may be called a fluid vibrating flowmeter. There are currently three types of fluid vibrating flowmeters: vortex flowmeters , precession (vortex precession) flowmeters, and jet flowmeters.
Vortex flowmeters have the following features:
1 The output is the pulse frequency, the frequency of which is proportional to the actual volumetric flow of the fluid being measured and is not affected by the fluid composition, density, pressure, and temperature;
2 wide measurement range, general range can reach 10:1 or more;
3 accuracy is in the upper level;
4 no moving parts, high reliability;
5 simple and solid structure, easy installation, low maintenance costs;
6 Wide range of applications for liquids, gases and steam.
The working principle of the vortex flowmeter : a vortex generating body (baffle) is set in the fluid, and a regular vortex is alternately generated from both sides of the vortex generating body. This vortex is called Karman vortex street, and the vortex is listed in the vortex. The occurrence body is arranged asymmetrically downstream. The pulse frequency signal output by the vortex flowmeter is not affected by the change of fluid properties and composition, that is, the meter coefficient is only related to the shape and size of the vortex generating body and the pipeline within a certain range of Reynolds number. However, mass flow needs to be detected in the material balance and energy metering. At this time, the flow meter should monitor the volume flow and the fluid density at the same time. The fluid properties and components will have a direct impact on the flow metering.
The vortex flowmeter consists of a sensor and a converter. The sensor includes a vortex generator (baffle), a detection element, and a meter body. The converter mainly includes a preamplifier, a filter shaping circuit, a DAC, and an output interface circuit. , terminals, brackets and protective covers. In recent years, smart flowmeters also place microprocessors, display communications, and other functional modules in the converter.
Vortex flowmeter application in the field:
1, field application
Vortex flowmeters are widely used fluids, but are not suitable for low Reynolds number (ReD ≤ 2 × 104) fluids. Because at the low Reynolds number, the Strouhal number changes with the Reynolds number and the instrument's linearity deteriorates. At the same time, the fluid containing the solid particles will generate noise to the vortex generator. The short fibers contained in the vortex generator will change the meter factor if they are wrapped around the vortex generator. The use of vortex flowmeters in mixed-phase fluids is as follows:
1 can be used to contain dispersed, uniform microbubbles, but the volumetric gas content should be less than 7% to 10% of the gas and liquid two-phase flow. If the volumetric gas content exceeds 2%, the meter factor should be corrected.
2 It can be used for gas-solid, liquid-solid two-phase flow with dispersed and uniform solid particles with a content of no more than 2%.
3 can be used for mutually insoluble liquid and liquid (such as oil and water) two-component flow and so on.
The pulsating flow and swirling flow will have a serious impact on the vortex flowmeter . If the pulsation frequency coincides with the frequency band of the vortex street, it may cause resonance, destroy the normal work and there is equipment, so that the vortex signal will generate a "lock-in" phenomenon, and the signal will be fixed at a certain frequency. The "locking" is related to the pulsation amplitude, the shape of the vortex body, and the clogging ratio.
The accuracy of vortex flowmeters is approximately ±0.5%R to ±2%R for liquids, and ±1%R to ±2%R for gases. The repeatability is generally 0.2% to 0.5%. Because the vortex flowmeter 's meter factor is relatively low, the frequency resolution is low, and the larger the caliber is, the lower the accuracy is, so the meter diameter should not be too large (below DN300).
Range is the characteristic of the vortex flowmeter , but the important point is the flow rate of the lower limit of the flow. The lower limit of the average flow rate of the general liquid is 0.5 m/s, and the gas is 4 to 5 m/s. The normal flow of the vortex flowmeter is preferably 1/2 to 2/3 of the normal measurement range.
The greatest advantage of vortex flowmeters is that meter coefficients are not affected by the physical properties of the measured medium and can be extended from a typical media to other media. However, due to the wide range of liquid and gas flow rates, the range of frequencies varies greatly. In the amplifier circuit that processes vortex signals, the pass band of the filter will be different, and the circuit parameters will also be different. Therefore, the parameters of the same circuit cannot be used to measure different media.
In addition, the density of gas and liquid varies greatly, and the intensity of the signal generated when the vortex is separated is proportional to the density, so the difference in signal intensity will also be large. The gains and triggering sensitivities of the liquid and air amplifier circuits are all different. Piezoelectric charge has a large difference, and the parameters of the charge amplifier will also be different. Even if the same gas (or liquid, vapor), with the media pressure, temperature, density, the flow range will be different, the signal strength is also different, the circuit parameters are also to be changed. Therefore, it is not feasible to change the use of media or change the gauge diameter of a vortex flowmeter without hardware or software modifications.
2, installation precautions
Vortex flowmeters are flowmeters that are sensitive to changes in the distribution of flow velocity in the pipeline, swirling flow, and turbulent flow. Therefore, attention should be paid to the installation conditions of the pipelines in the field and they must be strictly followed.
Vortex flowmeters can be installed indoors or outdoors. If it is installed in a well, a drowning type sensor should be used to prevent flooding. The sensor can be installed horizontally, vertically or obliquely above the pipe, but when measuring liquids and gases, attention should be paid to the mounting position in order to prevent air bubbles and droplets from interfering. Measurement of flow containing liquid and gas-containing liquid The installation of the instrument must ensure that the upper and downstream straight sections have the necessary length. Please pay attention to the following issues when connecting sensors and pipes.
1 The inner diameter D of the upper and lower piping is the same as the inner diameter D' of the sensor, and the difference must satisfy the following conditions: 0.95D≤D'≤1.1D;
2 piping should be concentric with the sensor, coaxial degree should be less than 0.05D';
3 The gasket cannot protrude into the pipe. Its inner diameter can be larger than the inner diameter of the sensor by 1~2mm.
4 If bypass inspection and cleaning sensor are needed, bypass piping should be provided;
5 Reducing the effect of vibration on vortex flowmeters should be a concern as a prominent issue in the field installation of vortex flowmeters . First of all, try to avoid the vibration source when selecting the sensor installation site; secondly, the elastic hose connection can be considered in the small diameter; thirdly, installing the pipe support is an effective method of vibration reduction.
Electrical installation should pay attention to the use of shielded cables or low-noise cables between the sensor and the converter, the distance should not exceed the provisions of the instructions. When wiring, keep away from strong power cables and try to protect them with a separate metal sleeve. The "one-point grounding" principle should be followed. The grounding resistance should be less than 10Ω. Both the integral type and the separate type should be grounded on the sensor side, and the converter housing ground point should be “in the same place” as the sensor.
3. Common faults, causes, and remedies at the site
Vortex flowmeter has a variety of detection methods, the sensor and the measurement circuit are also different, but common faults common to vortex flowmeters .
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