The IMGC-CNR flowmeter for automatic measurements of low-range gas flows

The IMGC-CNR constant pressure and variable volume gas flowmeter is described together with its automatic electronic control and data acquisition system. It is used to produce low pure-gas throughputs in the 10 −3–10 −8 Pa m 3 s −1 range, at the reference temperature of 294.15 K. This flowmeter may be used for both the pressure generation in the continuous-expansion system and for leak calibrations with reference to vacuum. Uncertainty evaluation is also discussed in the whole range of use, including the repeatability of the flowmeter itself: at present, the relative combined standard uncertainty ranges from a minimum value of 0.2% to a maximum of 0.8%.