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We describe a combined ultrasonic instrument for continuous gas flow measurement and simultaneous real-time binary gas mixture analysis. In the instrument, sound bursts are transmitted in opposite directions, which may be aligned with the gas flow path or at an angle to it, the latter configuration being the best adapted to high flow rates. The combined flow measurement and mixture analysis algorithm exploits the phenomenon whereby the sound velocity in a binary gas mixture at known temperature and pressure is a unique function of the molar concentration of the two components. The instrument is central to a possible upgrade to the present ATLAS silicon tracker cooling system in which octafluoropropane (\C3 {\F}8) evaporative cooling fluid would be replaced by a blend containing up to 25% hexafluoroethane (\C2{\F}6). The instrument has been developed in two geometries following computational fluid dynamics studies of various mechanical layouts. An instrument with 45^\circ crossing angle has been installed for commissioning in the ATLAS silicon tracker cooling system. It can be used in gas flows up to 20\thinspace000 l.min^-1 and has demonstrated a flow resolution of 2.3% of full scale for linear flow velocities up to 10 m.s^-1 in preliminary studies with air. Other instruments are currently used to detect low levels of \C3{\F}8 vapor leaking into the \N2 environmental gas surrounding the ATLAS silicon tracker. A long-duration continuous study of more than a year has demonstrated a sensitivity to mixture variation of better than 5.10^-5. [ABSTRACT FROM PUBLISHER]

Custom ultrasonic instruments have been developed for simultaneous monitoring of binary gas mixture and flow in the ATLAS Inner Detector. Sound transit times are measured in opposite directions in flowing gas. Flow rate and sound velocity are respectively calculated from their difference and average. Gas composition is evaluated in real-time by comparison with a sound velocity/composition database, based on the direct dependence of sound velocity on component concentrations in a mixture at known temperature and pressure. Five devices are integrated into the ATLAS Detector Control System. Three instruments monitor coolant leaks into N 2 envelopes of the silicon microstrip and Pixel detectors. Resolutions better than ± 2 × 10 − 5 and ± 2 × 10 − 4 are seen for C 3 F 8 and CO 2 leak concentrations in N 2 respectively. A fourth instrument detects sub-percent levels of air ingress into the C 3 F 8 condenser of the new thermosiphon coolant recirculator. Following extensive studies a fifth instrument was built as an angled sound path flowmeter to measure the high returning C 3 F 8 vapour flux ( ∼ 1.2 kgs − 1 ) . A precision of < 2.3 % FS for flows up to 10 ms − 1 was demonstrated. These instruments have many potential applications where continuous binary gas composition measurement is required, including hydrocarbon and anaesthetic gas mixtures. [ABSTRACT FROM AUTHOR]