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Model 9110T NOx Analyzer Principles of Operation
Teledyne Analytical Instruments 332
reaction cell.
O
3
supply inlet of reaction cell
Controls rate of flow of ozone gas into the
reaction cell.
0.004” (0.10 mm) 80 cm³/min
Dry air return of Perma Pure
®
dryer
Controls flow rate of dry air return / purge
air of the dryer.
0.004” (0.10 mm) 80 cm³/min
Vacuum manifold, Auto Zero port.
Controls rate of sample gas flow when
bypassing the reaction cell during the Auto
Zero cycle.
0.010” (0.25 mm) 500 cm³/min
Vacuum manifold, Internal span gas
generator exhaust port
Controls rate of flow of zero purge gas
through the optional Internal span gas
generator when it is installed.
0.003” (0.10 mm) 60 cm³/min
The necessary 2:1 ratios across the critical flow orifices is largely exceeded by the pumps supplied with
the analyzer which are designed to accommodate a wide range of possible variability in atmospheric
pressure and age related degradation of the pump itself. Once the pump does degrade the ratio between
sample and vacuum pressures may fall to less than 2:1. At this point, the instrument will display an
invalid sample flow rate measurement (XXXX).
Note The diameter of a critical flow orifice may change with temperature
because of expansion of the orifice material and, hence, the most crucial
critical flow orifices in the 9110T (those controlling the sample gas and O3
flow into the cell itself) are located in the reaction cell where they can be
maintained at a constant temperature.
13.2.3. OZONE GAS GENERATION AND AIR FLOW
The excess ozone needed for reaction with NO in the reaction cell is generated inside the analyzer
because of the instability and toxicity of ozone. Besides the ozone generator itself, this requires a dry air
supply and filtering of the gas before it is introduced into the reaction cell.
Due to its toxicity and aggressive chemical behavior, O
3
must also be removed from the gas stream
before it can be vented through the exhaust outlet.
CAUTION
GENERAL SAFETY HAZARD
Ozone (O
3
) is a toxic gas.
Obtain a Material Safety Data Sheet (MSDS) for this gas. Read and
rigorously follow the safety guidelines described there.
Always ensure that the plumbing of the O
3
generation and supply system
is maintained and leak-free.
13.2.3.1. The O
3
Generator
The 9110T uses a dual-dielectric, Corona Discharge (CD) tube for creating its O
3
, which is capable of
producing high concentrations of ozone efficiently and with low excess heat (see Figure 13-10). The
primary component of the generator is a glass tube with hollow walls of which the outermost and
innermost surfaces are coated with electrically conductive material.
Air flows through the glass tube, between the two conductive coatings, in effect creating a capacitor with
the air and glass acting as the dielectric. The layers of glass also separate the conductive surfaces from