Specifications

S
TARTUP AND
O
PERATION
748410-A
August 1999
19
Chemiluminescense Detector Analyzer Module
Rosemount Analytical NGA 2000
3
•
the converter is operating at too high a temperature and the nitrogen dioxide is reduced
to nitrogen, which is not detectable by the chemiluminescence reaction.
Initially, an interval of one week between converter efficiency checks is recommended
because 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 efficiency 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 located in the Physical Measurement
menu by selecting the following from the Main Menu: Expert Controls and Setup, Analyzer
Module Setup and Physical Measurement Parameters.
Follow this procedure to optimize the operating temperature of the converter:
1. Power up the module and allow it to stabilize at operating temperature (about one hour).
2. Check the Converter Temperature in the Physical Measurements menu (as noted
above). 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 Temperature Control menu to 300
°
C by selecting the
following from the Main Menu: Technical Configuration Menu, Diagnostic Menus,
Analyzer Module Diagnostics, Temperature Control Parameters. Allow module 15
minutes to stabilize, recheck the concentration value and note the value for later use.
5. Increase the Converter Setpoint value by 20
°
C, wait 15 minutes, and note the
concentration value. Repeat this step until either a converter efficiency of between 95%
and 98% is obtained or the final 20
°
C increment produces an efficiency increase of less
than one percent.
6. Decrease the Converter Setpoint value by 5
°
C, which places the converter at a
temperature suitable for low ammonia interference and efficient NO
2
conversion.
7. Recheck the Converter Temperature value in the Physical Measurements menu, and
compare it to the initially recorded value.
Converter temperature is not a direct measure of converter efficiency.
Temperature measurement is for reference purposes only.
NOTE