AVS 52nd International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuA

Paper VT-TuA2
Precise Volume Measurement of Bellows with its Length for a Constant Pressure Flowmeter

Tuesday, November 1, 2005, 2:20 pm, Room 200

Session: Calibration: Pressure and Flow Metrology
Presenter: K. Arai, AIST, Japan
Authors: K. Arai, AIST, Japan
H. Akimichi, AIST, Japan
M. Hirata, AIST, Japan
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A constant pressure flowmeter has been used to generate very low gas flow from 10@super -5@ to 10@super -10@ Pa m@super 3@ s@super -1@ as a reference standard to calibrate standard leaks. The rate of the flow is obtained by a volume change in a time while the pressure is kept constant. There are several methods to change the volume of the flowmeter. Bellows directly elongated and shortened by a pulse-driven linear actuator was used for precise measurements of the displacement and low outgassing due to the all-metal structure. In this study, the volume change in the bellows was measured as a function of its length by Boyle's law. The flowmeter was isolated from pumps and gas sources. The ratio of the volume change to the initial volume was obtained from the ratio of the pressures before and after shortening the bellows. The absolute value of the volume change was obtained from the difference of the pressure ratio by introducing a well-known volume (ball bearings). Pressure measurements were performed by capacitance diaphragm gauges (CDGs). The repeatability of the pressure ratio measurements was 3x10@super -5@, which was comparable to the chamber temperature fluctuation of 30 mK. The deformation of the bellows was caused by a pressure difference between inside and outside of the bellows. The pressure difference was kept under 2500 Pa by controlling the outside pressure. The remaining deformation was compensated by the value of the pressure difference. The volume change in the bellows by shorting it by 25.00 mm was 32.24 ml. The uncertainty of the measurement was 0.07% after consideration of the temperature fluctuation, the difference from the ideal gas and the thermal transpiration effect of the gauge. The volume changed with its length quadratically, as estimated from the structure of bellows.