Stanford Research Systems RGA100, Operating Manual And Programming Reference

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10 Appendix A
SRS Residual Gas Analyzer
RGA Table Scan
Ch# Name Mass Value Alarm Speed Cal CEM
NORMAL
3.8E-07
1 Hydrogen 2 1 1.00 OFF
HIGH
7.1E-08 2 Water 18 1 1.00 OFF
HIGH
1.4E-05
3 Nitrogen 28 1 1.00 OFF
NORMAL
4.6E-10
4 Oxygen 32 3 1.00 ON
NORMAL
3.4E-11
5 CO2 44 3 1.00 ON
NORMAL
1.6E-12 6 Oil 55 3 1.00 ON
NORMAL
1.5E-13
10 Floor 21 1 1.00 ON
Figure 5: SRS RGA Table Display
Leak Testing
In addition to the diagnosis of vacuum systems, the RGA is invaluable as an intrinsic leak
detector. It is always available and does not require perturbing the system. The user does
not have to roll up a large leak detector and attach it to the vacuum system. The system
does not have to be brought up to atmospheric pressure. The RGA can operate in leak
detection mode using any gas, so it does not require helium. For moderate leaks, argon
or tetrafluoroethane (a typical gas in cans of ““dust off””) can be used. Helium is necessary
for only the smallest leaks. Having a built-in leak detector makes working with vacuum
systems much easier and faster, and the SRS RGA is far less expensive than a standard
helium leak detector.
The process of leak detection with an RGA is the same as with a traditional helium leak
detector. Place the software in leak detection mode, indicate the mass of the test gas and
watch the partial pressure as various joints in the vacuum system are sprayed with the test
gas. When the leak is sprayed with the test gas, the partial pressure will rise. The
response is immediate if the leak is in a direct path from the outside to the inside of the
system. Figure 6 contains the result of a leak test with helium on a vacuum chamber. The
tester moves the helium probe towards and then past the leak, causing the first peak.
Once the location of the leak is bounded, the tester tries to precisely locate the leak. For
most situations leak testing is straightforward and no different than traditional methods.
In the following sections, we discuss a few situations where traditional methods fail and
how the RGA provides a better method.