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Title: Development Of The Primary Standard For Very Low Gas Flow Rates
Author: Shin-Ichi Nakao,Yoshiya Terao,Masaki Takamoto
Source: 2002 International Symposium on Fluid Flow Measurement
Year Published: 2002
Abstract: National Metrology Institute of Japan (NMIJ) has constructed a primary standard for gas flow rates less than 1 mg/min based on the dynamic gravimetric method. The whole calibration facility is set in the chamber to avoid the influences of the ambient air flow in the temperature controlled room. A gas vessel is hung from the high resolution balance and is connected to the piping outside the chamber by a Teflon tube. The vessel, with a volume of about 10 cm3, is pressurized up to 0.5 MPa at maximum. An automatic pressure controller (APC) is installed between the chamber outlet and a test flow meter (DUT) to regulate the pressure of the test gas flowing out from the vessel as a desired flow rate is obtained. The mass flow rate on the calibration can be calculated from the changing rate of mass of the gas vessel. The relative expanded uncertainty (coverage factor k2) of the primary standard developed is expected to be below 0.5 percent in the flow rate range from 1 mg/min to 0.05 mg/min.

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