Czech Metrology Institute (CMI) has developed (in cooperation with Charles University in Prague and company Vakuum Praha) a new primary high vacuum standard utilizing the dynamic (continuous) expansion principle. The standard is designed as a one step expansion system. The conductance is created by a circular orifice in a thin plate which edge region was formed by lapping with a sphere of diameter by 50 % larger than the orifice diameter, so the wall of the orifice has a concave form. Such shape was chosen for easy transmission probability calculation, whilst ensuring mechanical stability. Two constant pressure–variable volume flow meters with directly compressed diaphragm bellows of an original design were used to cover the whole required pressure range (10–5 to 10–1 Pa).
Our experience with development and metrological evaluation of this standard will be presented. Although the standard is based on classical design and takes advantage of long practice with such instruments in the national metrology institutes in the world, it brings some new improvements found out during its long time of development. These will be the focus of this contribution that will be supplemented by detailed analysis of sources of the uncertainties limiting its range and accuracy (expanded uncertainty below 1 %, in the range from 10–2 Pa to 5∙10–4 Pa) and performed comparisons. In the end our future plans for metrological ensure of the entire vacuum range will be briefly outlined.