Residual gas analyzer | |
Acronym: | RGA |
Uses: | Process gas measurement |
Manufacturer: | INFICON |
Model: | Transpector 200 |
A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed for process control and contamination monitoring in vacuum systems. When constructed as a quadrupole mass analyzer, there exist two implementations, utilizing either an open ion source (OIS) or a closed ion source (CIS). RGAs may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, etc. RGAs are used in most cases to monitor the quality of the vacuum and easily detect minute traces of impurities in the low-pressure gas environment. These impurities can be measured down to
10-14
RGAs would also be used as sensitive in-situ leak detectors commonly using helium, isopropyl alcohol or other tracer molecules. With vacuum systems pumped down to lower than
10-5
OIS is the most widely available type of RGA. Residual Gas Analyzers measure pressure by sensing the weight of each atom as they pass through the quadrupole. Cylindrical and axially symmetrical,[1] this kind of ionizer has been around since the early 1950s. The OIS type is usually mounted directly to the vacuum chamber, exposing the filament wire and anode wire cage to the surrounding vacuum chamber, allowing all molecules in the vacuum chamber to move easily through the ion source. With a maximum operating pressure of
10-4
10-14
OIS RGAs measure residual gas levels without affecting the gas composition of their vacuum environment, though there are performance limitations which include:
H2
With applications requiring measurement of pressures between
10-4
10-3
10-2
10-11
10-4
10-2
The CIS anode may be viewed as a high conductance tube connected directly to the process chamber. The pressure in the ionization area is virtually the same as the rest of the chamber. Thus the CIS ionizer produces ions by electron impact directly at the process pressure whilst the rest of the mass analyzer is kept under high vacuum. Such direct sampling provides good sensitivity and fast response times.