New, fully automated, primary standard for generating vacuum pressures between 10¹⁰Pa and 3   10²Pa with respect to residual pressure

Abstract

A new primary standard for the realization of vacuum pressures between 10-10 Pa and 3 × 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 degrees 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 × 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 × 10-3 at 10-10 Pa, when a perfectly stable residual pressure is assumed, to 2 × 10-3 at 10-4 Pa.