Precision ultrasonic measurements in binary gas systems provide continuous real-time monitoring of mixture composition and flow. Using custom microcontroller-based electronics, we have developed an ultrasonic instrument, with numerous potential applications, capable of making continuous high-precision sound velocity measurements. The instrument measures sound transit times along two opposite directions aligned parallel to - or obliquely crossing - the gas flow. The difference between the two measured times yields the gas flow rate while their average gives the sound velocity, which can be compared with a sound velocity vs. molar composition look-up table for the binary mixture at a given temperature and pressure. The look-up table may be generated from prior measurements in known mixtures of the two components, from theoretical calculations, or from a combination of the two. We describe the instrument and its performance within numerous applications in the ATLAS experiment at the CERN Large Hadron Collider (LHC). The instrument can be of interest in other areas where continuous in-situ binary gas analysis and flowmetry are required.

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 (C F ) evaporative cooling fluid would be replaced by a blend containing up to 25% hexafluoroethane (C 2 F 6 ). The instrument has been developed in two geometries following computational fluid dynamics studies of various mechanical layouts. An instrument with 45 crossing angle has been installed for commissioning in the ATLAS silicon tracker cooling system. It can be used in gas flows up to 20 000 l.min -1 and has demonstrated a flow resolution of 2.3% of full scale for linear flow velocities up to 10 m.s in preliminary studies with air. Other instruments are currently used to detect low levels of C 2 F 8 vapor leaking into the N 2 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 .

We describe a combined ultrasonic instrument for gas flow metering and continuous real-time binary gas composition measurements. The combined flow measurement and mixture analysis algorithm employs sound velocity measurements in two directions in combination with measurements of the pressure and temperature of the process gas mixture.The instrument has been developed in two geometries following extensive computational fluid dynamics studies of various mechanical layouts. A version with an axial sound path has been used with binary gas flows up to 230 l.min(-1), while a version with a sound path angled at 45 degrees to the gas flow direction has been developed for use in gas flows up to 20000 l.min(-1).The instrument with the axial geometry has demonstrated a flow resolution of <= 1 % of full scale for flows up to 230 l.min(-1) and a mixture resolution of 3.10(-3) for C3F8/C2F6 molar mixtures with similar to 20 %C2F6. Higher mixture precision is possible in mixtures of gases with widely-differing molecular weight (mw): a sensitivity of < 5.10(-5) to traces of C3F8 in nitrogen (mw difference 160) has been seen in a long duration (> 1yr) continuous study.A prototype instrument with 45 degrees crossing angle has demonstrated a flow resolution of 1.9 % of full scale for linear flow velocities up to 15 ms(-1).Although this development was motivated by a requirement of the ATLAS silicon tracker evaporative fluorocarbon cooling system, the developed instrument can be used in many applications where continuous knowledge of binary gas composition is required. Applications include the analysis of hydrocarbons, vapour mixtures for semi-conductor manufacture and anaesthetic gas mixtures.

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. Custom electronics based on Microchip® dsPIC and ADuC847 microcontrollers transmits 50kHz ultrasound pulses and measures transit times in the two directions together with the process gas temperature and pressure. 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 (C3F8) evaporative cooling fluid would be replaced by a blend containing up to 25% hexafluoroethane (C2F6). Such a blend will allow a lower evaporation temperature and will afford the tracker silicon substrates a better safety margin against leakage current-induced thermal runaway caused by cumulative radiation damage as the luminosity profile at the CERN Large Hadron Collider (LHC) increases. The instrument has been developed in two geometries following computational fluid dynamics studies of various mechanical layouts. An instrument with 45° crossing angle has been built in stainless steel and installed for commissioning in the ATLAS silicon tracker evaporative fluorocarbon cooling system. It can be used in gas flows up to 20000 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 C3F8 vapour leaking into the N2 environmental gas surrounding the ATLAS silicon tracker. Gas from several parts of the tracker is aspirated through two instruments and analyzed. A long duration continuous study of more than a year has demonstrated a sensitivity to mixture variation of better than 5.10-5. The developed instrument has many applications where continuous knowledge of binary gas composition is required. Such applications include anaesthesia, the analysis of hydrocarbon mixtures, and vapour mixtures for semiconductor manufacture.

Precision sound velocity measurements can simultaneously determine binary gas composition and flow. We have developed an analyzer with custom microcontroller-based electronics, currently used in the ATLAS Detector Control System, with numerous potential applications. Three instruments monitor C3F8 and CO2 coolant leak rates into the nitrogen envelopes of the ATLAS silicon microstrip and Pixel detectors. Two further instruments will aid operation of the new thermosiphon coolant recirculator: one of these will monitor air leaks into the low pressure condenser while the other will measure return vapour flow along with C3F8/C2F6 blend composition, should blend operation be necessary to protect the ATLAS silicon tracker under increasing LHC luminosity. We describe these instruments and their electronics.

The ATLAS silicon tracker community foresees an upgrade from the present octafluoropropane (C 3 F 8 ) evaporative cooling fluid to a composite fluid with a probable 10-20% admixture of hexafluoroethane (C 2 F 6 ). Such a fluid will allow a lower evaporation temperature and will afford the tracker silicon substrates a better safety margin against leakage current-induced thermal runaway caused by cumulative radiation damage as the luminosity profile at the CERN Large Hadron Collider increases. Central to the use of this new fluid is a new custom-developed speed-of-sound instrument for continuous real-time measurement of the C 3 F 8 /C 2 F 6 mixture ratio and flow. An acoustic vapour mixture analyzer/flow meter with new custom electronics allowing ultrasonic frequency transmission through gas mixtures has been developed for this application. Synchronous with the emission of an ultrasound `chirp' from an acoustic transmitter, a fast readout clock (40 MHz) is started. The clock is stopped on receipt of an above threshold sound pulse at the receiver. Sound is alternately transmitted parallel and anti-parallel with the vapour flow for volume flow measurement from transducers that can serve as acoustic transmitters or receivers. In the development version, continuous real-time measurement of C 3 F 8 /C 2 F 6 flow and calculation of the mixture ratio is performed within a graphical user interface developed in PVSS-II, the Supervisory, Control and Data Acquisition standard chosen for LHC and its experiments at CERN. The described instrument has numerous potential applications - including refrigerant leak detection, the analysis of hydrocarbons, vapour mixtures for semi-conductor manufacture and anesthetic gas mixtures.

An upgrade to the ATLAS silicon tracker cooling control system may require a change from C3F8 (octafluoro-propane) to a blend containing 10-30% of C2F6 (hexafluoro-ethane) to reduce the evaporation temperature and better protect the silicon from cumulative radiation damage with increasing LHC luminosity. Central to this upgrade is a new acoustic instrument for the real-time measurement of the C3F8/C2F6 mixture ratio and flow. The instrument and its Supervisory, Control and Data Acquisition (SCADA) software are described in this paper. The instrument has demonstrated a resolution of 3.10 -3