Instruction Manual
760000-C
November 2002
Rosemount Analytical Inc. A Division of Emerson Process Management Operation 3-37
Model NGA2000 CLD
3-12 CONVERTER TEMPERATURE ADJUST-
MENT
The vitreous carbon converter used in this
analyzer module must be checked periodically
to assure that it is working at peak efficiency.
The efficiency of the converter is typically 95%
to 98%, that is, 95% to 98% of the nitrogen
dioxide introduced to the module is reduced to
nitric oxide. That is well above the 90% mini-
mum required by the Environmental Protec-
tion Agency. (Refer to 40 CFR 60, App. A,
Method 20)
Two conditions reduce the efficiency of the
converter:
•
The converter is operating at too low a tem-
perature and the efficiency drops or
•
The converter is operating at too high a
temperature and the nitrogen dioxide is re-
duced to nitrogen, which is not detectable by
the chemiluminescence reaction.
Initially, an interval of one week between con-
verter efficiency checks is recommended be-
cause high temperature operation changes
conditions inside the converter. The active
surface area of the vitreous carbon increases
through use. Initially, when the surface area is
low, the temperature at which converter effi-
ciency peaks is relatively high. This peak
temperature moves downscale as surface
area increases, and less external energy is
required to cause adequate conversion.
The nominal range of converter operational
temperatures is 300
°
C to 400
°
C (572
°
F to
752
°
F). The current converter temperature
can be viewed in the “Physical measurement”
menu. To access the converter temperature
adjustment:
Main Menu
↓
Analyzer and I/O expert controls &
setup…
↓
Analyzer module setup…
↓
Physical measurements parameters…
Follow this procedure to optimize the operat-
ing temperature of the converter:
1. Power up the module and allow it to stabi-
lize at operating temperature (about one
hour).
2. Check the Converter Temperature in the
Physical Measurements menu (See Sec-
tion 3-7b, page 3-13). Note the value for
future reference.
3. Introduce a calibration gas of known
(NO
2
) concentration into the analyzer and
note the concentration value determined
when the full response has been
achieved.
4. Change Converter Setpoint in the “Tem-
perature Control” menu to 300
°
C (See
Section 3-11a, page 3-32). Allow module
15 minutes to stabilize, recheck the con-
centration value and note the value for
later use.
5. Increase the Converter Setpoint value by
20
°
C, wait 15 minutes, and note the con-
centration value. Repeat this step until ei-
ther a converter efficiency of between
95% and 98% is obtained or the final
20
°
C increment produces an efficiency in-
crease of less than one percent.
6. Decrease the Converter Setpoint value by
5
°
C, which places the converter at a tem-
perature suitable for low ammonia inter-
ference and efficient NO
2
conversion.
7. Recheck the Converter Temperature
value in the “Physical Measurements”
menu, and compare it to the initially re-
corded value.
NOTE
Converter temperature is not a direct
measure of converter efficiency. Tempera-
ture measurement is for reference pur-
poses only.
