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Product Spotlight

A Residual Gas Analyzer (RGA) is an instrument for measuring the partial pressures of gas species in a vacuum system.   It is really a MASS SPECTROMETER characterised by being small, robust and low cost.

The origins of RGA date back to the Manhattan Project circa 1942, initially using a magnetic sector field to separate ions of differing charge-to-mass ratio, but nowadays it is the quadrupole mass spectrometer that is usually at the heart of an RGA.

An RGA consists of three modules:

• An ion source, which can convert gas phase sample molecules into ions.
• A mass analyzer, which sorts the ions by their masses by applying electromagnetic fields.
• A detector, which measures the current of ions (rate of flow of charged particles).

The quadrupole mass filter is four rods (or hyperbolic electrodes) with the trajectory of ions along the central z-axis described by the Mathieu equations:

By applying RF + DC voltages to the rods, ions of one mass-to-charge ratio successfully find their way from the source (ionization) to the detector.  Sweeping the RF/DC amplitude produces a mass spectrum which provides a 'fingerprint' of the ions remaining in the vacuum environment.   The figure below diagrammatically shows the ion paths when the quadrupole filter is tuned to measure mass 28 ions (typically nitrogen).

RGA Benefits & Features

• Low cost mass spectrometer — a very powerful diagnostic tool and process monitor
• Leak Detector
• Vacuum Troubleshooter
• Process characterisation
• Understand your vacuum system:  water, outgassing, leaks (real & virtual), foreign objects
• Partial pressure analysis reveals actual contributions to Total Pressure
• Beware: RGA artefacts — Electron source, hot surfaces, ESD spurious peaks