AVS 49th International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuP

Paper VT-TuP6
Study of the Performance of a Precision Constant Volume Flowmeter for Vacuum Calibration and Measurement

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Poster Session
Presenter: Y.W. Chang, Precision Instrument Development Center, Taiwan, R. O. C.
Authors: Y.W. Chang, Precision Instrument Development Center, Taiwan, R. O. C.
J.S. Lin, Precision Instrument Development Center, Taiwan, R. O. C.
Correspondent: Click to Email
The Vacuum Laboratory at Precision Instrument Development Center in Taiwan has developed a high vacuum calibration and measurement system by the orifice flow method. A constant volume flowmeter is used to provide a measurable, steady and uniform gas flow to the vacuum chamber in the range 10@super -2@ to 10@super -5@ Torr.l/s. With this type of flowmeter gas is supplied from a reservoir of fixed and known volume. The pressure drop in the volume is measured and the product of reservoir volume and the pressure drop per unit time determines the gas throughput of flowmeter. A regulating valve at the exit of reservoir controls the gas flow rate. The performance of such a flowmeter is verified by introducing the known gas flow rate to an orifice calibration chamber to generate a pressure, which can be determined by the flow rate and the orifice conductance under molecular flow conditions. The predicted pressure is compared with the pressures simultaneously measured by a spinning rotor gauge calibrated at PTB in German and an ion gauge calibrated at NML in Taiwan. When the correction factors for two gauges show the same tendency in repeated measures, the variations of correction factors then indicate the performance of the flowmeter. The pressure drops in the reservoir are measured both absolutely and differentially. In absolute way the reservoir pressure is measured with a capacitance diaphragm gauge (CDG); while in differential way the pressure difference between the reservoir and a reference volume is measured with a differential CDG. The measurement results of gas throughput of the flowmeter by two ways are also presented in this study.