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1 March 1991 New apparatus and method for fluid composition monitoring and control
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Proceedings Volume 1392, Advanced Techniques for Integrated Circuit Processing; (1991)
Event: Processing Integration, 1990, Santa Clara, CA, United States
Acoustic pulses are generated at one end of acoustic waveguide tubes and detected at the other ends and the times required for the acoustic waves to traverse the gases contained in the tubes is measured. Several such waveguide tubes connected in series form an acoustic analyzer train. Individual components of a gas mixture are flowed serially into and through the analyzer train with one component added between each pair of individual acoustic analyzers. Thus the contents of each tube (except the first) is a binary mixture with one component being the contents of the previous tube and the other component being the gas which is added between the two adjacent tubes or at each stage of the blending process. TimeOf--Flight measurements are obtained at a frequency of about 100 Hz. with a technique which renders them independent of amplitude or gain factors. They are examined by several digital data quality assurance routines then converted to engineering units by a method called " ratiometric comparative sensing" . The results are substantially linear with respect to molecular fraction and free of all systematic error. Mechanically instrumentation has been developed which is compact and has an internal surface of welded stainless steel with no elastomeric seals of compression fittings. Internal surface to volume ratio is low compared to that of a thermal mass flow sensing unit. Transducer crystals (external) allow operation up to their
© (1991) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
John Urmson "New apparatus and method for fluid composition monitoring and control", Proc. SPIE 1392, Advanced Techniques for Integrated Circuit Processing, (1 March 1991);

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