Abstract
Described is the PVTt primary measurement standard used to calibrate primary standard critical flow nozzles with throat diameters from 2 mm to 8 mm over a flow rate range of 100 m3/h up to 1800 m3/h. Means and methods of the working standard critical flow nozzles calibration are considered. The metrological traceability chain for the gas flow measurements is presented. In the metrological traceability chain, the primary standards are the primary standard critical flow nozzles, the metrological characteristics of which are established through calibration using the primary measuring system and the primary measurement procedure. The secondary standards are working standard critical flow nozzles, the metrological characteristics of which are established by comparing them with primary standard nozzles. The metrological traceability chain has a branched structure, as the measurement model includes various physical quantities: pressure, temperature, volume, time, and gas properties.