GAS FLOW-RATE MEASUREMENTS FOR LEAK CALIBRATION

Results concerning the calibration of metal capillary tubes of the linear and crimped types with different inert testing gases from 3 x 10(-8) Pa m(3) s(-1) to 3 x 10(-5) Pa m(3) s(-1) (1 x 10(-11) mol s(-1)-1 x 10(-8) mol s(-1)) are presented. A primary flowmeter connected to a dynamic expansion system is used as a reference. With gas flow rates above 5 x 10(-7) Pa m(3) s(-1) (2 x 10(-10) mol (s-)1), direct comparisons are made, whereas for flow rates below that value the reduction method is applied. The unknown gas flow rates and those from the flowmeter are compared by means of a quadrupole mass spectrometer. These capillaries, after appropriate calibration, can be used as secondary reference leaks in the stated range with total uncertainty between 1.3 x 10(-2) and 9 x 10(-3) and the final object of this work is to provide a leak calibration service to users.