Zero Gas Module; Zeroing The Analyzer - Ametek 3050-AM User Manual

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. Function-
ally, the zero gas module is a very simple device, consisting of only three
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 ze-
roing 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 opera-
tion, 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 rela-
tively small—less than the equivalent of 0.1 PPMV.

Zeroing the Analyzer

The zero process is used to correct any offsets in the sample system. By
comparing the two zero readings (reference and sample) with the inter-
nally generated "zero" gas, any offset can be zeroed out. This is done by
measuring the zero offset frequency and storing it in memory. This offset
is then subtracted from ƒ before the sample moisture concentration is
calculated.
AMETEK recommends performing a zero every 24 hours for the first

month of operation. After this start-up period, the analyzer will have
dried down sufficiently to increase the zeroing interval to one week.
NOTE
AMETEK recommends that the duration of the zero cycle be set to
120 (i.e., 2 hours).
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