a Hirai Co. Ltd., System Division, Laboratory 2-80-1, Inadaira, Musashi-murayama, Tokyo 208-0023, Japan
b National Research Laboratory of Metrology, 1-4, Umezono-1, Tsukuba, Ibaraki 305-8563, Japan
Abstract:
We have developed a transfer standard system with sonic Venturi nozzles for small mass flow rates of gases. The system is composed of a newly developed automatic pressure controller, two pressure sensors and one temperature sensor to measure the flow conditions in the upstream and downstream sides of a nozzle. The whole system is packed in a portable aluminum trunk. The data are sent to a laptop computer, and the results are displayed on the screen and are written to files. The system can calibrate a flow meter in the flow rate range from 10 mg/min to 100 g/min using ten different sonic Venturi nozzles with the expanded standard uncertainty (k=2) being less than 0.2% for nitrogen. Examples of mass flow controller calibrations are given.