Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Probe Bakeout 8-5
SRS Residual Gas Analyzer
Probe Bakeout
Bakeout of the RGA probe is recommended in the following cases:
1. After installation of the probe in the vacuum chamber.
2. After prolonged exposure of the probe assembly to open air.
2. When background contamination is present in the mass spectra.
3. When the performance of the RGA is degraded due to excessive contamination.
When a new component is introduced into a high vacuum system or after the vacuum
chamber has been vented up to air, outgassing of molecules (particularly H
2
O) from the
walls usually determines the time it takes the pumping station to establish the desired
base pressure. A bakeout accelerates the outgassing rates and results in reduced pump-
down times.
In many cases a bakeout is needed to efficiently remove low-vapor pressure impurities
from the walls. A thorough bakeout helps clean the entire probe and usually results in
reduced contribution of the RGA sensor to the background signals.
As the RGA is used, deposits form on the ionizer parts and on the filter components. The
performance of the spectrometer is affected by the build-up of electrostatic charge on the
contaminated surfaces. The symptoms of the problem are: decreased sensitivity,
decreased resolution and, in severe cases, unusual peak shapes. A periodic bakeout helps
keep the quadrupole probe clean and minimizes this problem.
A thorough bakeout affects the entire probe. It is a better alternative than a ““Filament
Degas”” process which acts only on the ionizer and compromises the lifetime of the
filament.
Warnings
i
To avoid fire risk use a good quality heater with a built-in temperature limit switch.
i
The O100HJR 200 °C self regulating heater jacket is recommended for use with the
standard RGA nipple.
i
To avoid overheating the components use a reliable temperature controller to regulate
the bakeout temperature.
i
Do not leave the system unattended for long periods of time.
i
To avoid damage to the electronic components detach the ECU from the probe during
bakeout.
i
Do not operate the RGA during bakeouts.
i
To avoid burns cover the heater with heavy insulation during bakeout, and do not
touch the probe until it cools down after bakeout is over.
i
Use only metal gasket seals during bakeout since rubber gaskets might melt!