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Analysis of the influence of flow artery motion on vortex flowmeter

a. The effect of the pulsation frequency. When analyzing the influence of flow artery motion on the vortex flowmeter, the pulsation frequency is also an important parameter. The decisive factor is the ratio of the pulsation frequency to the vortex shedding frequency. When the ratio is small, it has approximate steady flow characteristics, and the vortex stripping frequency varies with the flow rate. Change, the Strohal number or the calibration constant does not change.
When the ratio of the pulsation frequency to the vortex shedding frequency is large, there is a strong tendency that the vortex shedding period is "locked" to the same write pulsation period (fv = fp) or half (fv - ≥ fp). Under the locked condition, the flowmeter output is paused, and the flow indication error can be as high as 80% of the soil. When the pulsation frequency is much higher than the vortex shedding frequency, there is no obvious locking phenomenon, but the Sterohal number changes, and the consequence is that the steady flow calibration data deviates significantly, reaching the order of 10_1.
Regarding the flow velocity pulsation amplitude U/m. The test data of /U indicates that this amplitude cannot exceed 20%. Regarding the definition of the pulsation frequency, at the lowest flow rate, the pulsation frequency should be less than 25% of the vortex shedding frequency.
b. The pulsating flow rate was measured using a vortex flowmeter. Attenuating the pulsation to a sufficiently small amplitude (usually 3%) using a suitable damping method is the most common and effective method of measuring pulsating flow using a vortex flowmeter. However, when the pulsation amplitude is still higher than 3%, the measurement uncertainty can be estimated and then the error corrected.
Locking caused by pulsation should be avoided. There are two feasible methods: one is to manufacture a vortex flowmeter with a narrower body, which increases the output frequency of the meter, so that the vortex stripping frequency is shifted farther from the pulsation frequency; the second is to use the plug-in vortex flow. Measuring large pipe runoff. At the same flow rate, the output frequency of the small-diameter flowmeter is several times higher than the large-diameter. Therefore, the vortex stripping frequency can be effectively shifted from the pulsation frequency by the plug-in vortex flowmeter.
c. Estimation of measurement uncertainty. If f, l fp<0. 25 and U'm. /U<o. 2, the measurement uncertainty is about 1%.
If f is much higher than fp, but there is no obvious locking phenomenon, the flow pulsation amplitude is o. 1No. Between 2, the error may be on the order of 10_1 of the flow indication.

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