Function and setup multi N/C 2100S
26
filled with special copper wool. The filling of the halogen trap has to be renewed at the
latest once half of the copper wool or the brass wool is discolored.
Fig. 14 Halogen trap
3.1.5 Detectors
The NDIR detector (NonDispersive Infrared absorption Detector) is behind the right-
hand side wall of the analyzer.
Gases with molecules from different atoms have specific absorption bands in the
infrared wavelength range. When a light beam is sent through an arrangement of cells
which contains gases in the IR active range, these gas components absorb the
characteristic wave lengths with their proportional part of the total radiation according
to their concentration part in the gas mixture.
The radiation receivers inserted in the used NDIR detector is selective for the CO
2
.
The CO
2
molecules are detected by the measuring technology as long as they remain in
the cell of the NDIR detector. Due to fluctuations of the measuring gas during the CO
2
measurement (e.g. on account of evaporation and condensation processes when
metering the liquid samples) CO
2
molecules are sometimes detected by spectrometry for
longer (low gas flow) or shorter (high gas flow) periods of time.
Using the VITA method (dwell time coupled integration for TOC analyses) the measuring
gas flow is detected parallel to the NDIR signal. Occurring flow variations are
compensated to a constant gas flow by computer-controlled normalization of the signal
and only integrated afterwards.
To this end, a high-accuracy, digital flow sensor is arranged very close to the NDIR
detector flow.
Measurements using the
VITA method
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