Eco Physics CLD 780 TR - Page 161

E C O P H Y S I C S Gas Phase Titration
CLD 780 TR / July 2000 158
[NO
x
]
OUT
= diluted NO
x
concentration at the output manifold, ppm
[NO
2
]
IMP
= concentration of NO
2
impurity in the standard NO cylinder,
ppm.
Carry out a calibration procedure as detailed in section 5.2.2.7.1.
Note: With the CLD 780 TR it is not necessary to enter a reference
value for NO
x
, since for both NO and NO
x
the same reaction
chamber is used for the measurement determinations (single-
chamber principle). If the NO calibration gas is uncontaminated
then the NO and NO.c signals are identical. If contamination with
NO
2
has occurred then the NO.c value will be higher.
3. Generate several additional concentrations (at least five evenly
spaced points across the remaining scale are suggested to verify
linearity) by decreasing F
NO
or increasing F
D
. For each concentration
generated, calculate the exact NO and NO
x
concentrations using
equations [9] and [10] respectively. Record the analyzer’s NO and
NO
x
responses for each concentration. Plot the analyzer responses
versus the respective calculated NO and NO
x
concentrations and
draw or calculate the NO and NO
x
calibration curves. For subse-
quent calibrations where linearity can be assumed, these curves
may be checked with a two-point calibration consisting of a zero air
point and NO and NO
x
concentrations of approximately 80 % of
the URL (zero and span check).
i) Preparation of NO
2
calibration curve: Press MEAS!
1. Assuming the NO
2
zero has been properly adjusted while sampling
zero air in step A3.5 g), adjust F
O
and F
D
as determined in section
A3.4. b). Adjust F
NO
to generate an NO concentration near 90 % of
the URL of the NO range. Sample this NO concentration until the
NO and NO
x
responses have stabilized. Measure and record the
NO concentration as [NO]
orig
, then measure and record the NO
x
concentration as [NO
x
]
orig
.
2. Adjust the O
3
generator to generate sufficient O
3
to produce a de-
crease in the NO concentration equivalent to approximately 80 %
of the URL of the NO
2
range. The decrease must not exceed 90 %
of the NO concentration determined earlier. After the analyzer re-
sponses have stabilized, record the resultant NO and NO
x
concen-
trations as [NO]
rem
and [NO
x
]
rem
.