Abstract
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.
Highlights
Ultrasonic binary vapour analysis was first used for the N2/C5F12 radiator of the SLD Cherenkov Ring Imaging Detector [6] and subsequently adopted in all major RICH detectors, including DELPHI, COMPASS, and LHCb, none of these applications exploited simultaneous flowmetry and vapour analysis in the same instrument
Custom timing electronics — internally implemented in the dsPIC33F microcontroller — generates 50 kHz ultrasound ’chirps’ and synchronously starts a 40 MHz transit time clock, which is stopped by the first pulse crossing the user definable threshold
The instrument has been implemented in several geometries, starting with a small “pinched axial” flow meter/analyzer [5] which has demonstrated a linearity of 2% of full scale for flows up to 230 litres per minute with simultaneous measurements of the C2F6 concentration in C2F6/C3F8 blends to a precision of ∼ 0.3%
Summary
Custom timing electronics — internally implemented in the dsPIC33F microcontroller — generates 50 kHz ultrasound ’chirps’ and synchronously starts a 40 MHz transit time clock, which is stopped by the first pulse crossing the user definable threshold (figure 3). The following comparator is implemented in the dsPIC33F microcontroller. This new configuration replaces a previous version, where the foil signal was ACcoupled to the first amplification stage, and allows shorter transit times to be measured through elimination of the waiting time associated with the discharge of a HV DC blocking capacitor. Bidirectional transit times, vapour temperature and pressure measurements are buffered, averaged, time-stamped, and pipelined by a FIFO memory implemented in the dsPIC33F microcon-
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