Rosemount Analytical NGA 2000 - Modulation Check

M
AINTENANCE AND
T
ROUBLESHOOTING
4-10
June 1997 Rosemount Analytical 748332-DNGA 2000 Non-Dispersive Infrared Analyzer
GAS DESICCANT PART NUMBER
CO
2
Cardoxide 096218
CO Mg (C10
4
)
2
096217
H
2
0Mg (C10
4
)
2
096217
SOS Mg (C10
4
)
2
096217
CH
4
Mg (C10
4
)
2
096217
Hexane Mg (C10
4
)
2
096217
CO + CO
2
Cardoxide + Mg (C10
4
)
2
096217/09621
4.13 CELL DESICCANT
The reference cell may use a flowing reference. If so, desiccant is required. A
desiccant holder is used on the inlet and outlets to keep moisture from entering the
reference cell (see Figure 4-7). The desiccant should be replaced each time the cell is
opened, refer to Table 4-1. Before inserting desiccant, purge cell with dry inert gas
(i.e., N
2
).
T
ABLE
4-1. C
ELL
D
ESICCANT
4.14 MODULATION CHECK
The modulation check is a measure of the energy absorption capacity of a gas
mixture, where total absorbency is 100% modulation and zero absorbency is 0%
modulation. The modulation check can be used as a tool for tracking the sensitivity of
the Analyzer Module and for discovering potential detector/source problems.
To perform a modulation check, do the following:
1. Access the Primary Variable Parameters menu (see Figure 3-13).
2. Select Modulation Check.
3. Follow the
Instructions
and
Then
line commands, which are the following:
a. Flow zero gas, press START softkey and wait.
b. Flow span gas when prompted, press START softkey and wait.
4. When the
Instructions
line again prompts the user to flow zero gas, the modulation
check is finished.
5. Note the value on the
Percent Modulation
line.
Find the Percent Modulation value on the Data Sheet in the rear of this manual. Some
standard Analyzer Modules will not have a value. If a value is present, compare this to
the new value.
If 100% span gas was used during the modulation check, the new value should be
within
±
10% of value on the Data Sheet. If it is out of this range, call the factory for
further interpretation. If modulation checks are used for trending, variance from check
to check should not exceed
±
20% per month.