Development of the calibration facility for small mass flow rates of gasesand the sonic Venturi nozzle transfer standard

A calibration facility based on the gravimetric method has been developed a t NRLM for small mass flow rates of gases. This calibration facility establ ishes a primary gas flow measurement standard in Japan with an expanded max imum uncertainty of +/- 0.12 percent for small mass flow rates from 0.1 g/m in to 50 g/min for nitrogen gas. Five sonic Venturi nozzles were tested usi ng this facility and the results showed that they can work well as a flow t ransfer standard for small mass flow rates. These sonic Venturi nozzles can be used to establish flow transfer standards within an expanded uncertaint y of +/- 0.15 percent.