Study on Leak Rate Formula and Criterion for Helium Mass Spectrometer Fine Leak Test

In the course of analyzing and deducing leak rate formula of fine leak test measurement of helium mass spectrometer, equivalent standard leak rate L is replaced with standard helium leak rate LHe . Helium gas exchange time constant zetaHe is cited, and the contents of typical gases inside hermetic cavity is calculated. It shows that after properly handling the measured leak rate deviation, a series of formulas of the paper can be used to perform engineering calculation on the process of gas exchange. zetaHes are calculated corresponding to leak rate criterion under various test conditions of current Chinese national military standards and US military standards in fine leak test of helium mass spectrometer, so real LHe is preferable to virtual L. Additionally, it is noted that zetaHe is the characteristic parameter to measure the relative hermeticity, and especially, most leak rate criterions in current military standards cannot guarantee meeting the requirement of internal vapor content, so by analyzing the improvement in the standards and existing hermeticity levels, it is evident that there still exists the necessity for the standards to be further improved.