Teledyne 9110T instruction manual Light Leaks

Model 9110T NOx Analyzer Principles of Operation

13.1.5.2. Third Body Quenching

As described by Equation 13-3, other molecules in the reaction cell can collide with the excited NO2*, causing the excited NO2* to return to its ground state without releasing a photon of light. This is known as third party quenching.

Quenching is an unwanted phenomenon and the extent to which it occurs depends on the properties of the collision partner.

∙Larger, more polarized molecules such as H2O and CO2 are the most significant quenching interferents of NO chemiluminescence.

∙The influence of water vapor on the 9110T measurement can be eliminated with an optional, internal sample gas dryer (see Section 3.3.2.6).

∙The interference of varying CO2 amounts at low concentrations (less that 0.5%) is negligible.

∙In cases with excessively high CO2 concentrations (larger than 0.5%), the effect can be calibrated out by using calibration gases with a CO2 content equal to the measured air.

∙Only very high and highly variable CO2 concentrations will then cause a measurable interference. For those applications, it is recommended to use other analyzer models. Please consult TAI Sales Department or our website (see Section 12.10).

∙Smaller less polar and electronically “harder” molecules such as N2 and O2 can cause interference of this type as well, however, the concentrations of N2 and O2 are virtually constant in ambient air measurements, hence provide a constant amount of quenching that is accounted for in the calibration of the instrument .

13.1.5.3. Light Leaks

The 9110T sensitivity curve includes a small portion of the visible light spectrum (see Figure 13-2), therefore it is important to ensure that the reaction cell is completely sealed with respect to light. To ensure this:

∙All pneumatic tubing leading into the reaction cell is opaque in order to prevent light from entering the cell.

∙Light penetration is prevented by stainless steel filters and orifices.

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