Gas flow standards and their uncertainty

Abstract

We review primary and working gas flow standards that are used to calibrate gas flow meters. For each type of primary standard, we describe the principles and practical considerations of its operation and describe one example implementation. We identify the practical limits of the example's performance, and, in many instances, we provide an uncertainty budget for a typical flow. The reviewed standards span the flow range 2.2 × 10-7 g/s to 520 kg/s. The references point to standards that operate at higher and at lower flows. The reviewed standards include volumetric flow standards (piston and bell provers, pressure-volume-temperature-time standards, rate of rise standards), static and dynamic gravimetric flow standards, and velocity × area standards such as critical flow venturis, laser doppler anemometer surveys, and multipath-ultrasonic meters. Finally, we describe working standard flow meters used in parallel to attain higher flows than economically practical via primary methods.

Calibration of gas flow meters using choked flow and an evacuated vessel

“…Although some researchers (Wright and Johnson 2000) do, in fact, see an increase in gas temperature of as much as 10 K, we do not observe that. It appears that they are filling their vessel to a higher pressure than we do, thus doing work on the gas.…”

“…Although our technique is quite similar to the PVTt method, there are some major differences. One difference is that it appears that the PVTt method has the gas entering the calibration apparatus at a pressure significantly higher than one atmosphere (at least for some calibrations), since they mention the increase in temperature of the gas as it enters the capturing tank or vessel and is compressed (Wright and Johnson 2000). Thus, the capturing vessel must be immersed in a temperature controlled water bath.…”