Leak detection, calibrations and reference flows: Practical example

The most diffused leak detection method for the leak rates lower than 10(-2) mbarL/s that is based on the application of mass spectrometry with tracer gas (generally helium) is considered. A description is given of the metrological characterization of the mass spectrometer leak detectors (MSLD) for industrial applications since they represent the best choice for tightening tests having good sensitivity and high testing speed. The calibration of MSLDs is performed with reference to known gas flow-rates as given by the so-called standard leaks which may generate flow from 10(-8) to 10(-2) mbar L/s; these leaks are calibrated against primary gas flow-meters which, at I.N.RI.M., cover the gas flow-rate ranges from 2 x 10(-8) to 1 x 10(-3) mbar L/s. As an example a device for on-line tests on components is presented together with the results of the calibrations against reference leaks of the MSLD alone and when it is inserted in a complete machine. By taking into account all the factors contributing to the uncertainty evaluation, a relative expanded uncertainty smaller than 20% may be reached.