Leak detection - Ultra sensitive techniques employing the Helium leak detector

The development of closures for electron devices often requires that leaks far below the range of the helium mass spectrometer type leak detector be localized and measured. It has been possible by using new techniques to extend the sensitivity of detection several orders of magnitude beyond the normal limit of the instrument. Two highly sensitive methods with similar techniques but separate sensitivity ranges are discussed. In seals similar to those of color television picture tube closures, it is noted that the kinetics of small leaks are such that long times are required to reach a constant maximum rate of helium leakage. Methods for predicting this maximum rate from early observations are discussed. Methods for establishing procedures necessary for sensitivity requirements for any particular seal type are given. Time and sensitivity limitations are discussed.