Intercomparison of gas flow-rate measurements at IMGC, Italy, and UASG, Germany, in the range from 10(-8) to 10(-3) Pa m(3)/s

Primary standard gas flow meters are developed for various applications Such as calibration of leak artefacts, generation of calibration pressures by dynamic gas expansion and calibration of secondary standard gas flow meters. The Istituto di Metrologia "G. Colonnetti" (lMGC), Italy, and the University of Applied Sciences Giessen-Friedberg (UASG), Germany, maintain primary flow meters based on different principles in order to measure small gas flows delivered either to vacuum (i.e. practically zero pressure) or to atmosphere (ambient pressure). The principle, design and properties of these flow meters are described. Comparison of the primary standard flow meters maintained at these laboratories was performed over a range from 3 x 10(-8) to 7 x 10(-4) Pa m(3)/s with nitrogen, using a crimped capillary leak as a transfer standard. IMGC was the pilot laboratory. During the intercomparison, the transfer standard changed by ca. -2% for flow to vacuum and by ca. -4% for flow to atmosphere without obvious reason. The results of the intercomparison show that the laboratories agree within their expanded uncertain ties over the measured range of gas flows