A new gross leak calibration for leak detectors

Abstract

The basic mechanisms of gas flow through leaks are described. Since many variables affect the sensitivity of a helium mass spectrometer leak detector, it is necessary that both fine leak (10−9 Pa m3/s) and gross leak (10−4 Pa m3/s) calibrations be performed (1 Pa m3/s=9.87 atm cc/s at 0 °C). Reference leaks are used to provide known rates of leakage which can be used to adjust leak detector sensitivity and ensure that specified maximum rates of allowable leakage can be detected reliably. Leakage from artificial leaks is used to calibrate the leak detector scales and in combination with unknown leakage from test objects or systems, permits quantitative measurement of leakage rates. Until recently none of the gross calibration standards available were acceptable. A precision gross leak calibrator has been designed that delivers gas into the leak detector at an absolute known rate. This simple device is convenient to use, has good repeatability, and a recalibration interval of three years.