Technical Information
2.5 Measurement Principle
LDS 6
22
Operating Instructions, 01/2009, A5E00295894-05
Relative absorption
Wavelength [μm]
1.543
1.5435
1.544
1.5445
1.545
1.5455
1.546
0.1
0.0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
H
2
O 15%
NH
3
5ppm
1.0
0.9
Figure 2-10 Absorption spectra of water and ammonia
Moreover, in some applications it is possible to determine the gas temperature as a
measured value. In this case, the ratio of the absorbance of two characteristic lines of the
same molecule measured at the same time in the same volume gives the actual temperature
in the process gas.
Typical measurable gases for LDS 6 are:
● Oxygen (O
2
) for low and high pressure
● temperature
● Hydrogen fluoride (HF) + water
● Hydrogen chloride (HCl) + water
● Ammonia (NH
3
) + water
● Water vapor (H
2
O)
● Carbon monoxide (CO)
● Carbon dioxide (CO
2
)
● CO + CO
2
By using an internal reference cell normally filled with the gas measured, the stability of the
spectrometer is permanently checked in a reference channel.
By doing so, the continuous validity of the calibration is ensured without the need to carry out
external recalibration using bottled test gases or reference gas cells.