Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Hardware modifications 3-17
SRS Residual Gas Analyzer
Hardware modifications
Warning
The information in this section is for the use of Qualified Personnel only. To avoid
shock and irreparable damage to the unit, do not attempt any of the changes in this
section unless you are authorized to do so.
Read and follow all ““Safety and Precaution”” instructions before handling the
product.
Because of the danger of introducing additional hazards, do not install substitute
parts or perform any unauthorized modification to the product. Do not use the
product if it has unauthorized modifications. Return the product to SRS for service
and repair to ensure that safety features are maintained.
The SRS RGA is a quadrupole mass spectrometer specially engineered to perform all the
functions of a residual gas analyzer, and its standard electron impact ionizer is designed
specifically for that type of operation. However, the simplicity of design of the probe
facilitates the modification of the instrument so that measurement applications other than
simple partial pressure analysis are possible. The relative insensitivity of quadrupole
mass filters to variations in ion entrance conditions makes it possible to apply quadrupole
mass spectrometers to the detection of ions from sources other than the standard electron
impact ionizers of RGA’’s. For example, quadrupole mass filters have been used to
monitor ion formation in plasma, SIMS, electrospray, ICP, laser ionization and surface
desorption experiments.
Many of the changes required to apply the RGA probe to alternative measurement
schemes involve the modification of the ionizer from its standard design. The ionizer is
of a very simple design and can be completely disassembled by the user loosening a few
screws (please see the RGA Maintenance chapter). Ease of disassembly is ideal for
periodic cleaning and very convenient when design modifications are needed. Special
applications might require modifying, replacing or even removing ionizer parts. The
scope of this section is to discuss the effects that design changes will have on the overall
performance of the probe. These types of modifications are most common in research
applications, and obviously
should only be attempted by qualified personnel who
completely understand the operation of the quadrupole mass spectrometer.
It is a good practice to minimize the changes performed on the probe so that the RGA can
still perform its basic functions of residual gas analysis, which are invaluable tools for
vacuum system diagnostics.
Repeller and anode grid modifications
The two ionizer grids can easily be removed from the probe for replacement or
modification. They are structurally very strong because they are made out of sintered
wire mesh (i.e. all crossing wires are welded to each other). Typical modifications, such
as punching holes or cutting slots, can be performed by skilled personnel without
compromising their shape. The replacements and modifications should obviously be
compatible with the operation of the rest of the quadrupole probe. Optimum performance
of the quadrupole can only be achieved if the ions are injected in the form of a beam of
low energy (2 to 15 eV) and low divergence (i.e. close to and parallel to the axis of the