GAS FLOW-RATE MEASUREMENTS FOR LEAK CALIBRATION

Results concerning the calibration of metal capillary tubes of the lin ear 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 a bove 5 x 10(-7) Pa m(3) s(-1) (2 x 10(-10) mol (s-)1), direct comparis ons are made, whereas for flow rates below that value the reduction me thod is applied. The unknown gas flow rates and those from the flowmet er are compared by means of a quadrupole mass spectrometer. These capi llaries, after appropriate calibration, can be used as secondary refer ence 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.