Properties and Specifications of Helium Leak Detectors

In principle, a helium leak detector detects the partial pressure of a tracer gas in vacuum with a suitable sensor. Small mass spectrometers have become common as a sensor, especially small magnetic sector-field mass spectrometers with permanent magnets. Also the quadrupole mass spectrometer well known from residual gas analysis can be found in some leak detectors. 

A mass spectrometer ionises all gas particles by means of electrons emitted from an incandescent filament. In a next step helium ions are filtered by a (magnetic or electric) separation system and are fed to an ion collector, which is coimected to a sensitive current amplifier that can measure and indicate the extremely tiny electrical current. 

The main specifications of a modern general-purpose leak detector are the following (the given data are typical for a good leak detector)  

Detection limit 5 X 10 mbar 1 s Helium pumping speed 11 s Maximum inlet pressure 5 mbar. 

Definitions of these specifications of helium leak detectors are given in Table 8.3. 

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