ABB AO2000-LS25 Laser analyzer

The measuring principle is infrared single-line absorption spectroscopy, which is based on the fact that each gas has distinct absorption lines at specific wavelengths. The measuring principle is illustrated in Figure 1-1. The laser wavelength is scanned across a chosen absorption line of the gas to be measured. The absorption line is carefully selected to avoid cross interference from other (background) gases. The detected light intensity varies as a function of the laser wavelength due to absorption of the targeted gas molecules in the optical path between transmitter and receiver. In order to increase sensitivity the wavelength modulation technique is employed: the laser wavelength is slightly modulated while scanning the absorption line. The detector signal is spectrally decomposed into frequency components at harmonics of the laser modulation frequency. The second harmonics of the signal is used to measure the concentration of the absorbing gas. The line amplitude and line width are both extracted from the second harmonics line shape, which makes the measured concentration insensitive to line shape variations (line broadening effect) caused by background gases.

NOTE: The AO2000-LS25 measures the concentration of only the FREE molecules of the specific gas, thus not being sensitive to the molecules bound with some other molecules into complexes and to the molecules attached to or dissolved in particles and droplets. Care should be taken when comparing the measurements with the results from other measurement techniques.

The transmitter unit contains the laser module with a temperature stabilized diode laser, collimating optics, and the main electronics in a coated Aluminum box.  

A block diagram of AO2000-LS25 is shown in Figure 1-3.

The receiver electronics is connected with the transmitter electronics with a cable.

AO2000-LS25 installation

Open the purging.