Instruction Manual
760000-C
November 2002
3-38 Operation Rosemount Analytical Inc. A Division of Emerson Process Management
Model NGA2000 CLD
3-13 MEASUREMENT OF CONVERTER EFFI-
CIENCY
It is the responsibility of the user to measure
efficiency of the NO
2
-to-NO converter during
initial startup and thereafter at intervals ap-
propriate 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 inter-
ference. 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
possible.
a.
Test Setup for Measurement of Con-
version Efficiency
A typical setup for measurement of con-
version efficiency is shown in Figure 3-67,
page 3-41. 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 full-scale 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. Al-
ternatively, a higher concentration NO
standard may be used if the test setup in-
cludes provision for diluting it appropri-
ately with zero air. Suitable standard
gases are available from various suppli-
ers. Stainless steel cylinders are com-
monly 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 oxy-
gen atoms, which can then combine with
atmospheric nitrogen to form NO. The re-
sult can be an erroneously high value for
the measured conversion efficiency.
b. Test
Procedure
1.
Measure converter temperature in
the sub-menu structure as de-
scribed in Section 3-7i, page 3-18.
Note present reading as a reference
for comparison with subsequent
readings.
2.
Lower converter temperature to
300
°
C as described in Section 3-
11a, page 3-32, Temperature Con-
trol Parameters, and wait 15 min-
utes for temperature equilibration.
3.
(See Figure 3-67, page 3-41) Con-
nect the Model 958 Converter Effi-
ciency 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 Mod-
ule inlet fitting to C3.
5.
With the variable transformer off,
switch the CLD Module to NO
mode, and close valve MV1.
6.
Open valve MV2 until the CLD
Module SAMPLE Pressure Gauge
reaches operating pressure and the
BYPASS flowmeter indicates some
bypass flow. Wait until stable read-
ings are obtained by the CLD Mod-
ule.
7.
Zero and span the Analyzer output
to indicate the value of the NO con-
centration being used. This value
should be about 80% of full-scale.
Record this concentration.
8.
Open valve MV1 (air supply meter-
ing valve) and adjust to blend
enough air to lower the NO concen-
tration (as noted above) about 10%.
Record this concentration.
9.
Power up the ozonator, and in-
crease its supply voltage until the
