A vacuum-driven gas gauge proximity sensor for sensing a difference
between a reference surface standoff and a measurement surface standoff
is disclosed. Unlike existing proximity sensors, the vacuum-driven gas
gauge proximity sensor uses a vacuum to reverse the traditional flow of
gas through a proximity sensor, such that gas flows inward across
measurement and reference standoffs through measurement and reference
nozzles. The conditioned ambient gas that is vacuumed into the reference
and measurement nozzles flows through reference and measurement channels
that are coupled at a junction into a single channel. The single channel
is coupled to the vacuum that is used to evacuate the conditioned ambient
gas through the proximity sensor. A bridge channel couples the reference
and measurement channels. A mass flow sensor along the bridge channel
monitors flow rates to detect measurement standoffs that can be used to
initiate a control action. A pump-driven liquid flow proximity sensor is
also disclosed.