A new primary standard for the realization of vacuum pressures between 10 -10 Pa and 3 ϫ 10 -2 Pa has been completed at the Physikalisch-Technische Bundesanstalt (PTB). It is based on the continuous expansion method, whereby the range is extended to lower pressures by the use of a flow divider. In this flow divider, the gas flow from the fully automated flowmeter with throughputs ranging from 10 -6 Pa l/s up to 3 Pa l/s (at 23 C) is directed via two differently sized orifices into two chambers: the XHV calibration chamber, which is designed for calibration pressures 10 -10 Pa to 10 -4 Pa, takes up 1 % of the flow, while the UHV calibration chamber, which is designed for pressures 10 -8 Pa to 3 ϫ 10 -2 Pa, takes up 99 % of the flow. Both calibration chambers are operated with cryopumps during calibration. The relative standard uncertainties of pressures generated by this new standard range from 7 ϫ 10 -3 at 10 -10 Pa, when a perfectly stable residual pressure is assumed, to 2 ϫ 10 -3 at 10 -4 Pa.
For applications in vacuum metrology, gas flowmeters have to deliver pure gas flows with well-known molar flow rates of low ( 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 Pa to Pa. It delivers gas flows with molar flow rates between mol/s and mol/s (throughputs Pa l/s to 3 Pa l/s at 23 C) with relative standard uncertainties ranging from 1.45 % at mol/s down to 0.14 % at mol/s.
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