Development of a transfer standard with sonic Venturi nozzles for small mass flow rates of gases

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 develope d automatic pressure controller, two pressure sensors and one temperature s ensor to measure the flow conditions in the upstream and downstream sides o f a nozzle. The whole system is packed in a portable aluminum trunk. The da ta are sent to a laptop computer, and the results are displayed on the scre en and are written to files. The system can calibrate a flow meter in the f low rate range from 10 mg/min to 100 g/min using ten different sonic Ventur i nozzles with the expanded standard uncertainty (k=2) being less than 0.2% for nitrogen. Examples of mass flow controller calibrations are given. (C) 2000 Elsevier Science Ltd. All rights reserved.