DEVELOPMENT OF A CALIBRATION FACILITY FOR SMALL MASS-FLOW RATES OF GAS AND THE UNCERTAINTY OF A SONIC VENTURI TRANSFER STANDARD

A calibration facility based on the gravimetric method has been develo ped at NRLM for small mass flow rates of gas. This calibration facilit y establishes a primary gas flow measurement standard with a combined standard uncertainty of +/-0.105% at maximum, for mass flow rates up t o about 5 g/min. Two differently sized sonic venturis were tested usin g this facility and the results show that they can work well as a flow transfer standard for small mass flow rates. It is also shown that th ese sonic venturis can be used to establish flow transfer standards wi th a combined standard uncertainty of +/-0.112% for the larger venturi and +/-0.089% for the smaller venturi. (C) 1997 Elsevier Science Ltd.