Teledyne API Model 200AH NO
X
Analyzer Instruction Manual, 06492, Rev. G2
4-1
4. THE M200AH NOX ANALYZER
4.1. Principle of Operation
4.1.1. NO
X
Measurement
The Teledyne API Model 200AH Analyzer is designed to measure the concentration of nitric
oxide [NO], total oxides of nitrogen [NO
x
] and, by calculation, nitrogen dioxide [NO
2
] (Note: the
calculation of NO
2
is not available in instruments equipped with the Oxygen measurement
option.) With the proper setup, it can operate in any of three sampling modes.
Table 4-1: Sampling Modes of the M200AH
Mode Description
NO/NO
X
switching mode
Converter is switched, measures NO, NO
x
, and NO
2
.
NO only mode
Converter is switched out of sample stream. Nitric Oxide is only
gas measured.
NO
x
only mode
Converter is switched into the sample stream, NO
x
is only gas
measured.
Regardless of which sampling mode the instrument is operating in, the signal from the M200AH
comes from the light emitted from the chemiluminescent gas phase reaction of nitric oxide [NO]
and ozone [O
3
] as follows:
223 O*NOONO
hvNO*NO 22
The reaction of NO with ozone results in electronically excited NO
2
molecules as shown in the
first equation above. The excited NO
2
molecules release their excess energy by emitting a
photon and dropping to a lower energy level as shown in the second equation. It has been shown
that the light intensity produced is directly proportional to the [NO] concentration present.
In the NO mode, the sample gas is routed directly into the reaction cell. Any NO gas present
reacts with ozone, producing light as described above.
In the NO
X
mode, the sample gas is routed through a NO
2
to NO converter, and any NO
2
present
is reduced to NO. The NO initially present remains as NO, therefore the signal is the sum of NO
and NO
2
present in the sample gas stream.
In the NO/NO
X
switching mode the Analyzer samples the gas stream and measures [NO]
concentration by digitizing the signal from the Analyzer's photomultiplier tube (PMT). The
