Teledyne T200, Operation Manual, Page: 298 / 425

Principles of Operation Teledyne API
– T200 NO/NO2/NOx Analyzer Operation Manual
296
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 T200 (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
G
ENERAL
S
AFETY
H
AZARD
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 T200 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 13-8). 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 the air stream to prevent reaction with the O
3
. As
the capacitor charges and discharges, electrons are created and accelerated across the air
gap and collide with the O
2
molecules in the air stream splitting them into elemental
oxygen.
Some of these oxygen atoms recombine with O
2
to O
3
. The quantity of ozone produced
is dependent on factors such as the voltage and frequency of the alternating current
applied to the CD cells. When enough high-energy electrons are produced to ionize the
O
2
molecules, a light emitting, gaseous plasma is formed, which is commonly referred to
as a corona, hence the name corona discharge generator.
06858E DCN7057