Abb-Lgr's Off-Axis Icos - ABB GLA232 Series User Manual

ABB LGR-ICOS™ GLA232 Series Methane/Ethane Analyzer User Manual
Integration of the measured spectra with the measured values of:

Gas temperature

Gas pressure

Path length

Line strength of the probed transition
Enables you to determine the mole fraction directly from the relation:
Use this equation to determine gas concentrations, even in hostile environments, without using
calibration gases or reference standards. These values are measured:

Mixtures containing several species

Flows at elevated temperatures and pressures

ABB-LGR's Off-Axis ICOS

Off-Axis Integrated-Cavity Output Spectroscopy (Off-Axis ICOS) uses a high-finesse optical cavity
as an absorption cell as shown in Figure 35. Unlike multi-pass detectors, typically limited to path
lengths of less than 200 meters, an Off-Axis ICOS absorption cell effectively traps the laser
photon so that, on average, photons make thousands of passes before leaving the cell.
As a result, the effective optical path length may be several thousands of meters using high-
reflectivity (HR) mirrors, thus, the measured absorption of light after it passes through the
optical cavity is significantly enhanced. For example, for a cell composed of two 99.99 percent
reflectivity mirrors spaced by 25 cm, the effective optical path length is 2500 meters.
Figure 35: Schematic Diagram of an Off-Axis ICOS Analyzer
ABB PROPRIETARY INFORMATION 49