New volumetric gas flow standard has reduced uncertainty. (General Developments).

A new pressure, volume, temperature, and time (PVTt) primary gas flow standard for calibrating flowmeters has an expanded uncertainty (k = 2) of between 0.02 % and 0.05 %. This uncertainty is approximately five times better than the previously existing primary flow standards and elevates the NIST gas flow calibration service to "best in the world" status. The standard diverts a steady flow into a collection tank of known volume during a measured time interval. The standard spans the flow range of i L/min to 2000 L/min using two collection tanks (34 L and 677 L) and two flow diversion systems. The new standard has several novel features that contribute to its low uncertainty. The thermostatted collection tank allows determination of the average gas temperature to 7 mK (0.0023 %) within an equilibration time of 20 min. The system utilizes a mass cancellation procedure that reduced the uncertainty contributions from the inventory volume to 0.017 % at the highest flow rate. Flows have been measured independently throughout the overlapping flow range of the two collection tanks, and they agree within 0.015 %. The new flow standard is automated and computer controlled so after set up, the meter calibration is unattended by the operator.

CONTACT: John Wright, [phone]; [e-mail].