The new UME primary standard for pressure generation in the range from 9X10(-4) Pa to 10(3) Pa

A new primary standard for generation of vacuum pressures between 9 x 10(-4) Pa and 10(3) Pa has been completed at the Ulusal Metroloji Enstitusu (UME). It is based on the static expansion method, whereby the range is extended to lower pressures by multiple expansions. The apparatus consists of six vessels that provide a pressure reduction by a factor of about 10(-6) in the main calibration vessel after a three-step expansion. Seventeen platinum resistance thermometers are mounted on the vessels to determine the correction due to temperature effects. The whole apparatus is built using the UHV technique and can be baked up to 400degreesC. The expanded (k = 2) relative uncertainties of pressures, generated by this new standard, range from 2.1 x 10(-3) at 9 x 10(-4) Pa to 9.5 x 10(-4) at 10(3) Pa.