Specifications

S
TARTUP AND
O
PERATION
748410-A
August 1999
20
Chemiluminescense Detector Analyzer Module
Rosemount Analytical NGA 2000
3
3.7 M
EASUREMENT OF
C
ONVERTER
E
FFICIENCY
It is the responsibility of the user to measure efficiency of the NO
2
-to-NO converter during
initial startup and thereafter at intervals appropriate to the application (normally once a
month).
The reactant material used in the converter provides the optimum combination of high
conversion efficiency and low ammonia interference. Unlike most competitive analyzers, the
NGA 2000 CLD Analyzer Module utilizes a reactant material that gradually becomes more
efficient at a given temperature. Thus, after a period of use, operation at a lower
temperature setpoint than initially required is certain.
3.7.1 T
EST
S
ETUP FOR
M
EASUREMENT OF
C
ONVERSION
E
FFICIENCY
A typical setup for measurement of conversion efficiency is shown in Figure 3-7. The test
setup includes:
A cylinder of nitric oxide standard gas consisting of NO in N
2
The concentration of NO in the standard gas should be about the fullscale value of the
range under test. The test sample supplied to the analyzer should contain a concentration of
NO comparable to that in the samples that are to be analyzed. Alternatively, a higher
concentration NO standard may be used if the test setup includes provision for diluting it
appropriately with zero air. Suitable standard gases are available from various suppliers.
Stainless steel cylinders are commonly used, but specially treated aluminum is preferred for
low parts-per-million NO samples.
An ozone generator utilizing an ultraviolet lamp, not a corona discharge
A corona discharge ozone generator is undesirable because it may produce oxygen atoms,
which can then combine with atmospheric nitrogen to form NO. The result can be an
erroneously high value for the measured conversion efficiency.
3.7.2 T
EST
P
ROCEDURE
1. Measure converter temperature in the sub-menu structure as described in Section 3.6.
Note present reading as a reference for comparison with subsequent readings.
2. Lower converter temperature to 300
°
C as described in Section 3.5, Step 4, and wait 15
minutes for temperature equilibration.
3. (See Figure 3-7) Connect the Model 958 Converter Efficiency Tester to the CLD Module,
and follow Steps 4 through 17 below (as adapted from 40 CFR 60):
4. Attach the NO/N
2
supply to C2, the air supply to C1, and the CLD Module inlet fitting to
C3.
5. With the variable transformer off, switch the CLD Module to NO mode, and close valve
MV1.