Stability tests of standard leaks for the calibration by a comparison method

At the calibration of standard leaks by a comparison method with reference standard leaks, important factors to evaluate the flow rates are the degrees of stability of a mass spectrometer leak detector (MSLD) and standard leaks. Stability of two leak element type standard leaks, a glass and a plastic, are tested. The test indicates that the warming up time is mainly influenced by the temperature of the mass spectrometer and 2 h is required to obtain a stabilized reading for the tested MSLD. In case of the glass type leak, 1 h pumping is required to obtain the stabilized flow rate after the exposure to the ambient air. In case of the plastic type leak, 1 min pumping is enough for the exposure time below 1 h but 6 h pumping is required after the 7 days exposure. After the valve closed duration within 3 h, the flow rates from both type of leaks recovered within a minute to 100% ± 0.5% of the averaged reading before the valve closed.

► The degrees of stability of the mass spectrometer leak detector (MSLD) and the standard leaks are investigated.
► The warming up time is mainly influenced by the temperature of the mass spectrometer.
► For the glass type leak, prior pumping for at least 1 h and in vacuum during the calibration is required.
► For the plastic leak, at least 6 h pumping before the calibration is required after the exposure for 7 days.
► Eliminating the effect of the exposure to the ambient air is important for the calibration of standard leak.