SRS Labs QMS 100 Series, Руководство пользователя

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What’s Inside ? 1–5
SRS QMS Gas Analyzer
a length of 0.9 m. Most of the capillary flow does not travel to the RGA, but is bypassed directly to the
diaphragm pump. A small part of this flow is drawn through a small aperture (60
µ
m diameter) into the
chamber where the RGA is located. The RGA chamber is maintained at approximately 10
-6
mbar by a
hybrid turbomolecular/drag pump. The flow through the RGA chamber is recombined with the flow that
was bypassed around the chamber. The recombination of the two flow streams is the key to the
compactness of the QMS instrument; without it, the system would require two pumps.
Figure 1-3. Schematic of gas flow.
The bypass flow configuration is also critical to the fast response time achieved by the QMS instrument.
A single stage pressure reduction with no bypass flow is possible using leak valves. These valves use
precision knife edges to create microscopic gaps. Such an inlet would draw gas at only 5
µ
l per minute
from atmospheric pressure into the RGA chamber. This flowrate is so small that the system would take
hours just to drain the volume in the body of the valve and result in an unusable response time. The
bypass flow configuration gives an exceptional response time of less than 0.2 seconds from the tip of the
capillary to the RGA chamber. The flexible capillary allows the inlet to be connected to remote
locations easily. Capillaries are available in a wide variety of materials and sizes for different
applications. The Technical Reference Manual contains guidelines for choosing the diameter and length
of custom capillaries.
Two solenoid valves control the gas flows. They can be set in four different combinations, and the
Operation section describes the use of each. The entire gas handling system is supervised by a
microcontroller, which assures that the valves and pumps are operated correctly.