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Model 9110T NOx Analyzer Troubleshooting & Service
Teledyne Analytical Instruments 293
12.7.10.2. NO
2
Conversion Efficiency
The efficiency at which the NO
2
NO converter changes NO
2
into NO directly effects the accuracy of
the 9110T’s NO
x
, NO and NO
2
measurements. The 9110T firmware includes a Converter Efficiency
(CE) gain factor that is multiplied by the NO
2
and NO
X
measurements to calculate the final
concentrations for each. This gain factor is stored in the analyzer’s memory.
The default setting for the NO
2
converter efficiency is 1.0000. Over time, the molybdenum in the NO
2
NO converter oxidizes and it becomes less efficient at converting NO
2
into NO.
To ensure accurate operation of the 9110T, it is important to check the NO
2
conversion efficiency
periodically and to update this value as necessary.
For the analyzer to function correctly, the converter efficiency must be between 0.9600 and 1.0200
(96-102% conversion efficiency) as per US-EPA requirements.
If the converter’s efficiency is outside these limits, the NO
2
converter should be replaced.
The current converter efficiency level is also recorded along with the calibration data in the DAS for
documentation and performance analysis (Section 7).
12.7.10.3. Calculating / Checking Converter Efficiency
The 9110T to automatically calculate the current NO
2
conversion efficiency by comparing a known
starting concentration of NO
2
gas to the measured NO output of the converter. There are three steps to
performing this operation.
Step 1:
Supply the analyzer with a known concentration of NO
2
gas, to the analyzer.
Figure 12-7: Setup for determining NO
2
NO Efficiency – 9110T Base Configuration
Step 2: