Teledyne 9110T instruction manual XNO2 + yMo→ xNO + MyOz at 315C

Model 9110T NOx Analyzer Principles of Operation

In order to measure the concentration of NO2, and therefore the concentration of NOx, the 9110T periodically switches the sample gas stream so that the pump pulls it through a special converter cartridge filled with molybdenum (Mo, “moly”) chips that are heated to a temperature of 315°C.

NO only

Figure 13-3: NO2 NO Conversion

The heated molybdenum reacts with NO2 in the sample gas and produces a NO gas and a variety of molybdenum.

Equation 13-4

xNO2 + yMo→ xNO + MyOz (at 315°C)

Once the NO2 in the sample gas has been converted to NO, it is routed to the reaction cell where it undergoes the chemiluminescence reaction described in Equation 13-1 and Equation 13-2.

By converting the NO2 in the sample gas into NO, the analyzer can measure the total NOX) content of the sample gas (i.e. the NO present + the converted NO2 present). By switching the sample gas stream in and out of the “moly” converter every 6 - 10 seconds, the 9110T analyzer is able to quasi- continuously measure both the NO and the total NOX content.

Finally, the NO2 concentration is not directly measured but calculated by subtracting the known NO content of the sample gas from the known NOX content.

13.1.4. AUTO ZERO

Inherent in the operation of any PMT is a certain amount of noise. This is due to a variety of factors such as black body infrared radiation given off by the metal components of the reaction cell, unit to unit variations in the PMT units and even the constant universal background radiation that surrounds us at all times. In order to reduce this amount of noise and offset, the PMT is kept at a constant 7° C (45° F) by a Thermo-Electric Cooler (TEC).

While this intrinsic noise and offset is significantly reduced by cooling the PMT, it is not eradicated. To determine how much noise remains, once every minute for about 8 seconds the 9110T diverts the sample gas flow directly to the vacuum manifold without passing the reaction cell.

Teledyne Analytical Instruments 322