Eco Physics CLD 780 TR - Page 160

E C O P H Y S I C S Gas Phase Titration
CLD 780 TR / July 2000 157
g) Adjust the GPT diluent air and O
3
generator air flows to obtain the
flows determined in Section A3.4. The total GPT air flow must exceed
the total demand of the analyzer(s) connected to the output manifold
to insure that no ambient air is pulled into the manifold vent.
Allow the analyzer to sample zero air until stable NO, NO
x
and NO
2
responses are obtained. The CLD 780 TR has an automatic zero ad-
justment. With NO-free zero air, the response should be zero (within
the detection limit).
Note: Because of the special characteristics of the CLD 780 TR analy-
zer it is necessary to introduce the term „NO.c“, by which the total
quantity of NO converted from NO
x
in the photolytic converter (PLC) is
implied. NO.c differs from the quantity usually designated „NO
x
“
through the following relationships:
1. NO.c
≈
NO + NO
2
x W
K
i.e. negligible interference from other N-
containing substances
2. Converter efficiency W
K
<100 %
h) Preparation of NO and NO
x
calibration curves. Entering of NO and
NO
x
reference values:
1. NO concentration:
Adjust the flow from the standard NO cylinder to generate an NO
concentration of approximately 80% of the upper range limit (URL)
of the NO range. The exact NO concentration is calculated from:
[NO]
OUT
= ( F
NO
x [NO]
STD
) / ( F
NO
+ F
O
+ F
D
)[9]
where:
[NO]
OUT
= diluted NO concentration at the output manifold, ppm.
2. NO
x
concentration:
The presence of any NO
2
impurity in the standard NO cylinder must
be taken into account when entering the analyzer’s NO
x
reference
value. Procedures for determining the amount of NO
2
impurity in
the standard NO cylinder are given in Reference 1. The exact NO
x
concentration is calculated from:
[NO
x
]
OUT
= ( F
NO
x
{
[NO]
STD
+ [NO
2
]
IMP
}
) / ( F
NO
+ F
O
+ F
D
) [10]
where: