LAUSR

According to the mission of the national reference laboratory, LNE-CETIAT achieved in 2012 the construction and accreditation of a modern and innovative calibration laboratory based on the gravimetric method. The measurement capabilities cover a flow rate range for liquid from 10 kg h−1 down to 1 g h−1 with expanded relative uncertainties from 0.1% to 0.6% (k = 2). Since 2012, several theoretical and experimental studies have allowed a better knowledge and control over uncertainty sources and have decreased calibration time. When dealing with liquid micro-flow using a reference method such as the gravimetric method, several difficulties have to be overcome. The main improvements described in this paper relate to the enhancement of the evaporation trap system, the merging of the four dedicated measurement lines into one, and the implementation of a gravimetric dynamic 'flying' method for the calculation of the reference flow rate. The evaporation-avoiding system has been replaced by an oil layer in order to remove the possibility of condensation of water on both the weighed vessel and the immersed capillary. The article describes the experimental method used to quantify the effect of surface tension of water/oil/air interfaces on the weighed mass. The traditional static gravimetric method has been upgraded by a dynamic 'flying' gravimetric method. The article presents the newly implemented method, its validation and its advantages compared to the static method. The four dedicated weighing devices, dispatched over four sub-ranges of flow rate, have been merged leading to the use of only one weighing scale with the same uncertainties on the reference flow rate. The article discusses the new uncertainty budget over the full flow rate range capability. Finally, the article discusses the improvements still under development and the general prospects of liquid micro-flow metrology.