We compared 20 m3 and 2 m3 facilities of pVTt methods gas flow primary prover (pVTt prover) in Flow lab of National Institute of Metrology of China (NIM). We used sonic critical venturi nozzle (sonic nozzle) as transfer standard. The flow points of comparison are about 100 nm3/h and 150 nm3/h. We completed four comparison tests whose results are considered acceptable, whereas we found there was a little systematic error between the two facilities.
