A dynamic gravimetric standard for liquid flow measurements

An improved primary method for the calibration of liquid flow meters based on dynamic weighing has been adopted at the Istituto Nazionale di Ricerca Metrologica. Compared to the other dynamic methods currently in use, based on submerged liquid jet flows, the proposed method has the advantage of not requiring the correction for the hydrostatic buoyancy force exerted on the immersed tube. This is possible since the immersion depth of the tube is held constant during the dynamic weighing process, entailing, consequently, a constant back pressure at the outlet section of the immersed tube and a more stable liquid meniscus at the tube outer surface, which both improve the accuracy of measurement. Although at present the proposed apparatus has been tested in the range between 10 kg h−1 and 60 kg h−1, this improved dynamic method would be particularly suitable for lower flow rate as well. The results have shown that relative uncertainties of the order of 0.01% can be obtained.