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Zero Gas Module
The Zero gas module, shown inside of the dotted rectangle in Figure 1-2, is
used to provide a dry gas stream at the inlet of the analyzer. Functionally, the
Zero gas module is a very simple device, consisting of only three (3) diaphragm
valves and a dryer. The diaphragm valves used in this device are UHP grade
components; all surfaces are electropolished, and the gas connections are
welded. Because of the high quality of the surfaces in these components,
residual moisture retention is minimized. Therefore, the assembly is capable of
rapidly achieving a dry condition once the Zeroing cycle has been initiated.
Under normal operation of the analyzer, both DV1 and DV3 remain closed to
protect the dryer, while DV2 is open to allow the flow of Sample gas into the
analyzer. When performing the Zeroing operation, DV2 is closed, while both
DV1 and DV3 are open. Thus, the flow of Sample gas is diverted through the
dryer, providing a dry reference (<10 PPBV) for the analyzer. By providing
this dry Reference gas, the Zero gas module enables the offsets present in the
system (e.g., electronic offsets, offsets caused by pressure differences in the
different flow paths, and offsets caused by low-level outgassing of water vapor
from upstream valving) to be measured. Normally, the magnitude of these
offsets is relatively small – less than the equivalent of 0.035PPMV.
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Overview
1-7
PN 305804902, Rev A
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