Evaluation of uncertainty in a vortex flowmeter measurement

Abstract

Measurement results of all quantities are inevitably subject to uncertainties. Proper estimation and expression of uncertainties are important to every domain of scientific and engineering researches. In this paper, the uncertainty of a vortex flowmeter was evaluated based on a novel mathematical measurement model and airflow experiment results. The proposed model was featured by regarding the vortex flowmeter and its calibration equipment as an entire measurement system, on which the uncertainty evaluation was carried out. The experiments were conducted in a 50-mm-diameter pipe with the Reynolds numbers from 9.42×103 to 8.48×104, and vortex frequencies were calculated by spectrum analysis of the differential pressures obtained on the pipe wall. The uncertainty analysis procedure followed the recommendations in the ISO Guide to the Expression of Uncertainty in Measurement. The results show that in the flowrates studied, the maximal uncertainty of the tested vortex flowmeter is less than 6.0% of the base value. Besides, higher measurement uncertainty takes place at lower flowrates, and the uncertainty appears to be constant when the flowrate is greater than a certain value. Among the relevant uncertainty sources, frequency resolution causes the biggest contribution to the total uncertainty especially at lower flowrates, and the uncertainty arose from the calibration system is less minor compared with uncertainties associated with the vortex frequency. It indicates that an effective strategy of reducing the uncertainty caused by the vortex frequency is improving its resolution, accordingly reducing the total uncertainty of a vortex flowmeter measurement.