Development of vacuum metrology in National Institute of Metrology

► NIM has developed the static expansion system, leak rate standard and micro-manometer in recent years. ► The reference volume method is first introduced in determining the volume ratio of the static expansion system. ► The thermal transpiration effect of CDG is round 3%∼4% for pressure from 1 Pa to 100 Pa. ► An adjustable micro-conductance from 1 × 10−7 m3/s to 1 × 10−6 m3/s is realized by the clearance of a piston-cylinder unit.