A new fully automated gas flowmeter at the PTB for flow rates between 10-13 mol/s and 10-6 mol/s

For applications in vacuum metrology, gas flowmeters have to deliver pure gas flows with well-known molar flow rates of low (< 10(-6) mol/s) and very low values. Accurate flowmeters are used to generate pressures in continuous expansion systems, to measure leak rates, and to measure pumping speeds of ultrahigh-vacuum pumps. At the Physikalisch-Technische Bundesanstalt (PTB) a new, fully automated, all-metal flowmeter was commissioned for use with a continuous expansion system in the pressure range 10(-10) Pa to 3 x 10(-2) Pa. It delivers gas flows with molar flow rates between 4 x 10(-13) mol/s and 10(-6) mol/s (throughputs 10(-6) Pa l/s to 3 Pa l/s at 23 degreesC) with relative standard uncertainties ranging from 1.45% at 4 x 10(-13) mol/s down to 0.14% at 10(-6) mol/s.