Ozone Scrubber; Flow Rate Control - Critical Flow Orifices - Teledyne 200E Instruction Manual

Model 200E Instruction Manual
sensitivity drift, nitric acid is a very aggressive compound, which can deteriorate the
analyzer's components. In order to remove these chemical byproducts from the O
stream, the output of the O
and the reaction cell.
Any NO that may be produced in the generator (from reaction of O
X
and may cause an artifact in the measurement, is calibrated out through the Auto-zero
functionality, which checks the background signal of the O

10.2.8. Ozone Scrubber

Even though ozone is unstable and typically reacts to form O
fast enough to ensure that it is completely removed from the exhaust gas stream of the
M200E by the time the gas exits the analyzer. Due to the high toxicity and reactivity of O
a special catalytic ozone scrubber is used to remove all of the O
Besides its efficient destruction of O
gases as it only converts ozone to oxygen and it also does not pose an explosion hazard like
charcoal scrubbers.
The O scrubber is located inside the NO
3
order to utilize residual heat given of by the converter heater. Even though the catalyst is
100% efficient at scrubbing ozone at room temperature, heating it significantly reduces the
necessary residence time (the amount of time the gas must be in contact with the catalyst)
for 100% efficiency and full efficiency can be maintained at higher gas flow rates. As this is
a true catalytic converter, there are no maintenance requirements as would be required for
charcoal-based scrubbers.
A certain amount of fine, black dust may exit the catalyst, particularly if the analyzer is
subjected to sudden pressure drops (for example, when disconnecting the running pump
without letting the analyzer properly and slowly equilibrate to ambient pressure). To avoid
the dust from entering the reaction cell or the pump, the scrubber is equipped with sintered
stainless steel filters of 20 µm pore size on either end and on some models, an additional
dust filter may be attached to the exhaust port.

10.2.9. Flow Rate Control - Critical Flow Orifices

In order to maintain constant flow rates for both the O
M200E uses a variety of flow control assemblies located at various key places in the
pneumatic system of the instrument (Figure 10-9).
The most important component of each flow control assembly is the critical flow orifice.
Critical flow orifices are a simple means to regulate stable gas flow rates. They operate
without moving parts by taking advantage of the laws of fluid dynamics. By restricting the
flow of gas through the orifice, a pressure differential is created. This pressure differential,
created by the analyzer's external pump, draws the gas through the orifice.
As the pressure on the downstream side of the orifice (the pump side) continues to drop,
the speed of the gas flowing through the orifice continues to rise. Once the ratio of
upstream pressure to downstream pressure is greater than 2:1, the velocity of the gas
through the orifice reaches the speed of sound and remains constant, regardless of any
further pressure difference. As long as that ratio stays at least 2:1, the gas flow rate is
unaffected by fluctuations, surges, or changes in downstream pressure because such
044100102 Rev A
generator flows through a special filter between the generator
3
, this catalyst does not produce any toxic or hazardous
3
converter housing next to the NO
2
Theory of Operation
or O
2 3
stream only once per minute.
3
, the break-down is not quite
2
exiting the reaction cell.
3
supply air and the sample gas, the
3
gas
3
and N in the air)
2
,
3
converter in
2
167