Development of a custom on-line ultrasonic vapour analyzer/flowmeter for the ATLAS inner detector, with application to gaseous tracking and Cherenkov detectors

Precision sound velocity measurements can simultaneously determine binary gas composition and flow. We have developed an analyzer with custom electronics, currently in use in the ATLAS inner detector, with numerous potential applications. The instrument has demonstrated similar to 0.3% mixture precision for C sub(3)F sub(8)/C sub(2)F sub(6) mixtures and < 10 super(-4) resolution for N sub(2)/C sub(3)F sub(8) mixtures. Moderate and high flow versions of the instrument have demonstrated flow resolutions of plus or minus 2% of full scale for flows up to 250 1 min super(-1), and plus or minus 1.9% of full scale for linear flow velocities up to 15 m s super(-1); the latter flow approaching that expected in the vapour return of the thermosiphon fluorocarbon coolant recirculator being built for the ATLAS silicon tracker.