Endress+Hauser Analytik Jena multi N/C, Руководство по эксплуатации, Страница: 22 / 106

Function and setup multi N/C pharma UV
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Fig. 11 Halogen trap
3.1.5 NDIR detector
The NDIR detector (non-dispersive infrared absorption detector) is on the rear right
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 active IR range, these gas components absorb the
characteristic wave lengths with their proportional share of the total radiation
according to their concentration 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