Teledyne 9110T instruction manual Measurement Interferences, Direct Interference

Model 9110T NOx Analyzer Principles of Operation

During this time, only O3 is present in the reaction cell, effectively turning off the chemiluminescence reaction. Once the chamber is completely dark, the 9110T records the output of the PMT and keeps a running average of these AZERO values. This average offset value is subtracted from the raw PMT readings while the instrument is measuring NO and NOX to arrive at an Auto Zero corrected reading.

Figure 13-4: Pneumatic Flow During the Auto Zero Cycle

13.1.5. MEASUREMENT INTERFERENCES

It should be noted that the chemiluminescence method is subject to interferences from a number of sources. The 9110T has been successfully tested for its ability to reject interference from most of these sources. Table 13-1 list the most common types of interferents that could affect the performance of your 9110T.

13.1.5.1. Direct Interference

Some gases can directly alter the amount of light detected by the PMT due to chemiluminescence in the reaction cell. This can either be a gas that undergoes chemiluminescence by reacting with O3 in the reaction cell or a gas that reacts with other compounds and produces excess NO upstream of the reaction cell.

Teledyne Analytical Instruments 323