Mass Spectrometry

The heart of the most sensitive and accurate instrument for detecting extremely small leaks is the mass spectrometer, which is used to measure the rate of flow of a tracer gas through leaks using vacuum, pressure or vacuum-pressure techniques. The mass spectrometer detects the tracer gas and converts it to an electrical signal proportional to the size of the leak. Helium is usually used as a tracer gas because of its unique combination of properties:

• Helium is extremely rare in the atmosphere, so there is little ambient “noise” to interfere with leak measurement
• Non-explosive, non-toxic, completely inert (no contamination of the tested product)
• Will not contaminate and desensitize its own detector as is common with detectors using other tracers
• Helium is a small, light molecule (mass 4) and will flow readily through extremely small leaks