E C O P H Y S I C S Operating Guide
CLD 780 TR / July 2000 40
Details of the individual modes:
– “NO“: This mode serves to determine and display the nitrogen monox-
ide (i.e. nitric oxide, NO) concentration in the sample gas. The elec-
tronic and chemical zero point is continuously determined and cor-
rected for, eliminating NO interferences.
– “NO.c“: The sample gas is passed through a PLC 762 photolytic con-
verter before entering the CLD 780 TR analyzer. Only NO.c is meas-
ured and displayed. NO.c is the raw value of the sample gas NO
x
concentration after passing through the converter and consists of the
sum of the NO and NO
2
signals. The NO
2
contribution in NO.c is not
adjusted for the converter efficiency (W
K
).
NO.c = NO + NO
2
x W
K
In this mode also the electronic and chemical zero point is continuously
determined and corrected for, eliminating NO.c interferences.
– “NO and NO.c“: In alternating cycles the NO and NO.c concentra-
tions in the sample gas are measured and displayed. The details given
above for the NO and NO.c modes are still valid. The cycle duration
for the NO and NO.c determination can be set indirectly in window
(24) under “Integration Interval“.
– “NO and NO
2
“: In alternating cycles the NO and NO.c concentra-
tions in the sample gas are measured and displayed. The nitrogen di-
oxide (NO
2
) content is calculated from the NO.c value and the con-
verter efficiency as last determined. (The effect of ozone in the sample
gas is not taken into account.)
– “NO (cont.)“: In this mode, only the effective nitrogen monoxide con-
tent of the sample gas is measured and displayed. All the options
which can be set in windows (5) to (13) are active, e.g. the displayed
NO data may be smoothed using a sliding average filter (see windows
(9) and (13)). The electronic and chemical zero point is evaluated and
corrected for as per the settings in the “AICI“ window (7). This elimi-
nates the effect of interferences in the sample, assuming the concentra-
tion of the interfering substances varies directly with the NO concentra-
tion between two AIC measurements, thus ensuring that the factor
λ
NO
remains constant (see window (58)).
The analytical basis of the “Continuous measuring mode“ is described
in detail in Appendix A5.
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