CALCULATED AND EXPERIMENTAL ZERO STABILITY OF A CORIOLIS FLOWMETER RELATED TO THE ELASTIC AND DAMPING PROPERTIES OF ITS FIXTURE
Keywords:
Coriolis flowmeter, zero shift, finite element method, damping, calculation of forced oscillationsAbstract
Coriolis flowmeters determine the mass flow rate by measuring the phase shift or time delay between pick-off signals. Therefore, any change in the phase shift unrelated to fluid flow contributes to the mass flow error. Error sources can include external influences and non-idealities in the flow tubes. The earlier experimental studies of the effect of the flowmeter fixation strength on the result of mass flow measurement, we observed an unacceptable increase in the measurement error, which is associated with the zero shift of the device. We found that this increase is due to the coincidence of one of the natural frequencies of the “coriolis flowmeter-pipelines” system with the drive frequency, related to the fixation strength. The paper is devoted to the analysis of the zero shift, which is observed when one of the natural frequencies of the “coriolis flowmeter-pipelines” system gets into the drive frequency range.
We developed a beam-shell finite element model of the “coriolis flowmeter – pipelines” system, and calculated its steady forced oscillations. Based on this model, we established that the zero shift is influenced by three factors: the proximity of the two frequencies, the value of damping, and the imbalance of the two measuring tubes. In the case of coincidence of the two frequencies, there is more than double increase in phase difference between the two corresponding points of the measuring tubes on the drive form. It is caused by an increase in the vibration amplitude of the flowmeter body and a change in the oscillation phase of the body by 1800. The calculation results were confirmed experimentallyReferences
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