Generation of a stable vacuum pressure by flow method using micro capillaries

A stable vacuum pressure is necessary to calibrate a vacuum gauge by direct comparison. Three flow methods to generate a vacuum pressure are examined; by using a variable leak valve, a mass flow controller and a micro capillary in conjunction with a precise pressure controller for the calibration of a spinning rotor gauge. The fluctuation of generated pressure by using a micro capillary in conjunction with a pressure controller is 0.01%-0.22%, that is the most stable of three methods, and the adjustable pressure range is more than 4 orders, from 3times10^-4 Pa to 5 Pa. The two-stage flow method using two capillaries in series is also examined to generate a stable ultra-high vacuum (UHV) pressure for the calibration of an ionization gauge. The fluctuation of generated UHV pressure lies within the range from 0.1% to 0.6% corresponding to the pressure from 2times10^-7 Pa to 6times10^-3 Pa. The fluctuations are mainly determined by the resolution of the digital indication of the ionization gauge