Raman Spectroscopy and
the Laser Gas Analyzer at work

In 1928 Indian Physicist C. V. Raman demonstrated that monochromatic light passing through a substance scatters and produces a spectrum that is unique to that substance. Raman found that bands appearing in the spectrum distinctively characterize the chemical composition of the substance illuminated.

Since the 1960s the precisely monochromatic light emitted by lasers has enabled numerous scientific and industrial applications of spectroscopy based on Raman’s work to detect and quantify the presence of chemical compounds in solids and liquids.

ARI’s Laser Gas Analyzer exploits the phenomenon that gas molecules struck by laser light absorb it and re-emit light at frequencies different from the laser. The molecular bonds of each gas molecule uniquely determine the resulting “Raman Shift” frequency(ies) of the re-emitted light. The shifts are so discrete and precise that the intensity of light observed at various shifted frequencies is directly proportional to the concentrations of constituent molecules in the atmosphere.

The heart of the Laser Gas Analyzer is a detector module that shines a safe, low-power laser through a gas sampling chamber. The chamber has eight ports, each fitted with an optical filter and light sensor to measure the intensity of light at a specific frequency.

When an atmosphere sample is analyzed pumps draw the gas to the sampling chamber. A media filter at the intake removes particulate contaminants.

In the chamber the gases pass through the laser beam, and the molecules emit their characteristic light signatures. Electronics for each light sensor provide a digital signal quantifying its particular gas component.

The detector is connected to a specially-built computer that logs, interprets and displays the sensor data. The computer typically communicates with the control systems for the equipment being monitored and controlled.

Custom-fitted piping and a proprietary valve manifold subsystem connect the detector to the phyiscal environment being measured. The valve manifold assures that the gas samples drawn from multiple sources and locations each are presented uncontaminated to the sampling chamber.

Gas Process Real-Time Control

ARI’s Laser Gas Analyzer and Controller combines the LGA with existing process gas control valves and safety systems on site.

The system monitors process conditions and adds process gas in response to reaction needs in real time. This ability results in tighter control of reactive processes as well as the opportunity to reduce process gas consumption significantly.

Because the system measures all types of reactive gases in near-real time, accurate atmosphere control of industrial gas processes can become easier to understand and control.

For example, when used with non-standard atmosphere mixtures for heat treating, the sophisticated control enables improvements in processing speed from 20% to 50%, enhancing heat treating facility bottom-line profits by 25% and more.

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