US Patent 8675168 Gas gauge compatible with vacuum environments

A gas gauge (100) is provided for use in a vacuum environment having a measurement gas flow channel (105). The gas gauge comprises a measurement nozzle (110) in the measurement gas flow channel (105). The measurement nozzle (110) is configured to operate at a sonically choked flow condition of a volumetric flow being sourced from a gas supply (120) coupled to the measurement gas flow channel (105). The gas gauge (100) further comprises a pressure sensor (127) operatively coupled to the measurement gas flow channel (105) downstream from the sonically choked flow condition of the volumetric flow to measure a differential pressure of the volumetric flow for providing an indication of a gap (130) between a distal end of the measurement nozzle (135) and a target surface (140) proximal thereto.