Laser spectroscopic oxygen sensor using diffuse reflector based optical cell and advanced signal processing |
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Authors: | J Chen A Hangauer R Strzoda M-C Amann |
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Institution: | 1. Corporate Research and Technology, Siemens AG, Otto-Hahn-Ring 6, 80200, Munich, Germany 2. Walter Schottky Institut, Technische Universit?t München, Am Coulombwall 3, 85748, Garching, Germany
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Abstract: | In this paper, an improved signal processing method is given, aiming at a sensitivity improvement of the tunable diode laser
spectroscopy based gas concentration measurement. The gas absorption spectrum is probed with an optimum wavelength scanning
function which enables a more efficient curve fit than for traditional linear wavelength scanning. The wavelength scanning
function is determined to be optimum, in the sense that the variance of the estimated concentration noise is minimized. This
optimum scanning function depends on the signal model used in curve fitting. Several models including interfering gas spectra
and etalon fringes are examined. Compared to the gas absorption spectrum recorded by ramping the wavelength linearly, the
optimum spectrum waveforms have a cascade structure, which means that the optimum scanning preferably samples important points
of the spectrum. The new method theoretically enables a factor of ∼2 improvement on detection sensitivity of the estimated
concentration. Furthermore, direct spectroscopy is superior to second harmonic detection, because the concentration noise
can be an additional factor of ∼2 lower. |
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Keywords: | |
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