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13.
PRINCIPLES OF OPERATION
13.1. MEASUREMENT PRINCIPLE
13.1.1. CHEMILUMINESCENCE CREATION IN THE T200 REACTION CELL
06858E DCN7057
The T200 Nitrogen Oxides Analyzer is a microprocessor controlled instrument that
determines the concentration of nitric oxide (NO), total nitrogen oxides (NO
of NO and NO
) and nitrogen dioxide (NO
2
instrument.
It requires that sample and calibration gases be supplied at ambient atmospheric
pressure in order to establish a constant gas flow through the reaction cell where
the sample gas is exposed to ozone (O
light (hv).
The instrument measures the amount of chemiluminescence to determine the
amount of NO in the sample gas.
A catalytic-reactive converter converts NO
with the NO present in the sample is reported as NO
difference between NO
Calibration of the instrument is performed in software and usually does not require
physical adjustments to the instrument. During calibration, the microprocessor measures
the sensor output signal when gases with known amounts of NO or NO
and stores these results in memory. The microprocessor uses these calibration values
along with the signal from the sample gas and data of the current temperature and
pressure of the gas to calculate a final NO
The concentration values and the original information from which it was calculated are
stored in the unit‟s internal data acquisition system (DAS Section 7) and are reported to
the user through a vacuum fluorescence display or several output ports.
The T200‟s measures the amount of NO present in a gas by detecting the
chemiluminescence which occurs when nitrogen oxide (NO) is exposed to ozone (O
This reaction is a two-step process:
In the first step, one molecule of NO and one molecule of O
react to produce one molecule of oxygen (O
(NO
). Some of the NO
2
from the collision and exist in an excited state, where one of the electrons of the
NO
molecule resides in a higher energy state than normal (denoted by an asterisk
2
in the following equation).
) in a sample gas drawn through the
2
), initiating a chemical reaction that gives off
3
in the sample gas to NO which, along
2
and NO.
X
concentration.
X
) and one molecule of nitrogen dioxide
2
molecules created by this reaction retain excess energy
2
, the sum
X
. NO
is calculated as the
X
2
are supplied
2
collide and chemically
3
)
3
.
283
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