Instruction Manual
June 2007
NGA 2000 CLD
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 % minimum required by several Environmental Protection Agency.
Two conditions reduce the efficiency of the converter:
•The converter is operating at too low a tempera- ture and the efficiency drops or
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 on the Physi- cal Measurements menu (see Section
3.Introduce a calibration gas of known (NO2) con- centration into the analyzer and note concentra- tion value determined when the full response has been achieved.
•The converter is operating at too high a tempera- ture and the nitrogen dioxide is reduced to nitro- gen, which is not detectable by the chemilumines- cence 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 temperature 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...
4.Change Converter Setpoint in the "Temperature Control" menu to 300 °C. Allow module 15 min- utes 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 suit-
able for low ammonia interference and efficient NO2 conversion.
7.Recheck the Converter Temperature value in the "Physical Measurements" menu, and compare it to the initially recorded value.
NOTE
Converter temperature is not a direct measure of converter efficiency. Temperature measurement is for reference purposes only.
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