Volumetric positive-displacement gas flow standard

A new volumetric standard system has been developed capable of calibrating gas flow meters continuously. It is made of double concentric spheres. The inner sphere defines a basic volume that is divided into two parts by a fle xible diaphragm. A water draw method used to measure this volume gave 25.34 3 l with l ml uncertainty. A changing pressure signal causes a change of fl ow direction every cycle. A careful treatment of this transient signal prov ides corrections to the basic formula for the mass flow rate. An uncertaint y analysis of the new standard system shows that the most important factor is air temperature. Multiple nozzles were calibrated singly and in parallel by the new system to check the upper limit of the flow rate which is about 2 m(3)/h with 0.15% expanded uncertainty. (C) 2001 Elsevier Science Ltd. A ll rights reserved.