AVS 59th Annual International Symposium and Exhibition
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP11
Expanded Capability of Measuring Pumping Speed of Dry Vacuum Pumps Using Calibrated Sonic Nozzles

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Session: Vacuum Technology Poster Session and Student-built Vacuum System Poster Competition
Presenter: W.S. Cheung, KRISS, Korea
Authors: W.S. Cheung, KRISS, Korea
S.H. Nam, KRISS, Korea
W.J. Kim, KRISS, Korea
J.Y. Lim, KRISS, Korea
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This paper addresses technical issues in expanding the capability of measuring the pumping speed of dry vacuum pumps using a built-up block of multiple calibrated sonic nozzles. The first challenging issue comes from the technical limit that their calibration results available from the flow measurement standard laboratories do not fully cover the low vacuum measurement range of 10 ~ 1000 mbar although the use of sonic nozzles for precision measurement of gas flow has been well established in national metrology institutes. In order to tackle the first technical issue, the constant volume flow measurement method dedicated for the vacuum range of 10 ~ 1000 mbar is exploited to calibrate the discharge coefficient multiplied by the cross-section area of each sonic nozzle used in the built-up block of sonic nozzles. On the other hand, the discharge coefficient multiplied by the cross-section area of each sonic nozzle in the upstream pressure range of 2 ~ 10 bar is calibrated in the gas flow standard laboratory. These combined calibration methods are illustrated to enable each sonic nozzle to cover the three decade measureable range 10 mbar ~ 10 bar.The second technical issue comes from a logical way of stacking multiple sonic nozzles to expand the capability of measuring the pumping speed of dry vacuum pumps. A target value of the upper limit of pumping speed in this work was selected to be 4,500 m3/h as the Korean flat display manufacturers requested to KRISS. On the onset of this work, sonic nozzles of 5 mm throat diameter were machined to fulfill the upper limit pumping speed by stacking three or four nozzles in the built-up block. Of course, small sized nozzles (0.1, 0.16, 0.5, and 1.0 mm throat diameter) were also machined in this work to cover the low and mid range of the throughput of 0.1 ~ 100 mbar-l/s. A prototype of the built-up block with the capacity of installing six sonic nozzles simultaneously is under test. Its design throughput was to be about 125,000 mbar-l/s. This prototype is expected to provide a possible ‘on-line pumping speed tester’ with the capability of 4,500 m3/h or more, applicable not only to the on-site flat display processes but also to the semiconductor processes.