Bilateral comparison of gas microflow primary standards in the range between 0.12 mg/min and 2.4 mg/min

A bilateral comparison of small gas flow rates in the range between 0.12 mg/min and 2.4 mg/min was performed between INRiM (Italy) and LMPS (Slovenia). The primary standard at INRiM is a type of a motor driven piston prover. The primary standard at LMPS is a pVTt method with a static mass determination and flying start-stop. The transfer standard main part are two capillary leaks, with measuring ranges up to 0.25 mg/min and 2.5 mg/min respectively. A Hagen-Poiseuille equation with a constant geometric factor is used to calculate the mass flow rate. The comparison was carried out at five measurement points with the large capillary leak and at two points with the small capillary leak. The results show that there are statistically significant differences between the measurements of the two laboratories. The estimated uncertainties are also too large to confirm the target CMCs, as the repeatability of the measurements was too weak.