Calibration of flow devices is important in several areas of pharmaceutical, flow chemistry and microfluidic applications where dosage of process liquids or accurate measurement of the flow rate is important. The process-oriented liquid itself might influence the performance of the flow device and the simultaneous determination of the dynamic viscosity under flow conditions might be a valuable information for the process parameters. To offer the simultaneous calibration of the dynamic viscosity of the process-oriented liquid at the corresponding flowrate, METAS has built a pipe viscometer for the traceable in-line measurement of the dynamic viscosity in the current flow facilities for low flow rates from 1 L/min to 150 mL/min and pressure drops up to 10 bar. The traceability of all the measuring quantities as well as the geometrical dimensions of the micro tube guarantee the traceability of the pipe viscometer to SI units. The most challenging part is the traceable determination of the inner diameter of the micro tube. This can be achieved by measuring the pressure drop as a function of flow rate with the pipe viscometer and applying the law of Hagen-Poiseuille with a traceable dynamic viscosity of a reference liquid (water) or perform the measurements with the micro-CT at METAS, which determines the inner diameter by x-ray diffraction. The validation of the stated measurement uncertainty of the pipe viscometer has been performed by means of calibration of the dynamic viscosity of several reference liquids with traceable density and kinematic viscosity. The setup of the facility, the traceability as well as the uncertainty calculation of the pipe viscometer for the in-line measurement of the dynamic viscosity are discussed in this paper.

Main text: This bilateral comparison compares volume gas flow measurements in the range (1.2 to 450) mL/min@STP using Laminar Flow Elements as the main part of the transfer standard. The goal is the evaluation of the degree of equivalence of the participating laboratories INRIM and METAS at every flow measuring point. The comparison was successfully completed and confirmed the current CMC entries for both laboratories. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A large hydrogen infrastructure is currently in development across Europe. However, the industry faces the dilemma that they are required to meet certain measurement requirements set by European legislation that cannot currently be followed due to the lack of available methods and standards. The EMPIR Metrology for Hydrogen Vehicles project will be the first large scale project of its kind that will tackle the four measurement challenges that currently prevent the industry from meeting requirements set by International Standards such as flow metering, quality control, quality assurance and sampling. This paper presents a brief overview of the specific objectives of the project and focuses on the flow metering work package and the presentation of its planned tasks, which comprise laboratory and measurements in the field. Laboratory work will assess the use of substitute fluids to hydrogen to provide a safer and more cost effective method for the type approval of Hydrogen Refuelling Stations (HRS). To be able to link laboratory work to field testing, mobile primary standards will be developed and the design of a field testing primary standard will be addressed. The aim is to inform what the European national metrology institutes are currently developing in the field of hydrogen flow metering and quality control of HRS.