Instruction Manual
748214-V
June 2009
Rosemount Analytical Inc. A Division of Emerson Process Management Installation 1-1
Model 951C
SECTION 1
DESCRIPTION AND SPECIFICATIONS
1-1 OVERVIEW
The Model 951C NO
X
Analyzer is designed to
measure NO
X
using one of three sets of ranges
designated as Hi, Mid, or Lo. The Hi Range set
consists of spans with ranges of 0-100, 0-250,
0-1000, and 0-2500 ppm NO
X
. The Mid Range
set consists of spans with ranges of 0-20, 0-50,
0-200, and 0-500 ppm NO
X
. The Lo Range set
consists of spans with ranges of 0-10, 0-25,
0-100, and 0-250 ppm NO
X
.
The NO
X
analyzer continuously analyzes a flow-
ing gas sample for NO
X
[nitric oxide (NO) plus
nitrogen dioxide (NO
2
)]. The sum of the concen-
trations is continuously reported as NO
X
.
The analyzer is based on the chemilumines-
cence method of NO detection. The sample is
continuously passed through a heated bed of
vitreous carbon, in which NO
2
is reduced to NO.
Any NO initially present in the sample passes
through the converter unchanged, and any NO
2
is converted to an approximately equivalent
(95%) amount of NO.
The NO is quantitatively converted to NO
2
by
gas-phase oxidation with molecular ozone pro-
duced within the analyzer from air supplied by
an external cylinder. During this reaction, ap-
proximately 10% of the NO
2
molecules are ele-
vated to an electronically excited state, followed
by immediate decay to the non-excited state,
accompanied by emission of photons. These
photons are detected by a photomultiplier tube,
which in turn generates a DC current propor-
tional to the concentration of NO
X
in the sample
stream. The current is then amplified and used
to drive a front panel display and to provide po-
tentiometric and isolated current outputs.
To minimize system response time, an internal
sample-bypass feature provides high-velocity
sample flow through the analyzer.
The Backlight blinks when the analyzer is 10%
or more over-range. Selecting a less sensitive
(higher) range restores the display function.
The case heater assembly of the Model
951C maintains the internal temperature at
approximately 50
o
C (122
o
F).
1-2 TYPICAL APPLICATIONS
The Model 951C Analyzer has specific ap-
plications in the following areas:
• Oxides of nitrogen (NO
X
)
emissions from the combustion
of fossil fuels in:
• Vehicle engine exhaust
• Incinerators
• Boilers
• Gas appliances
• Turbine exhaust
• Nitric acid plant emissions
• Ammonia in pollution control
equipment (with converter)
• Nitric oxide emissions from
decaying organic material (i.e.,
landfills).
