Gas measurement over extreme dynamic range of concentrations,
U. S. Patent 7,616,316, issued November 10, 2009
Gas analyzers often need to work over a very wide range of concentrations. For instance, when searching for a natural gas leak, sensitivity comparable to the natural background (about 2 parts per million) is needed. But as the leak is tracked to its source, the concentration can grow to 100%. Another example is measuring water vapor in the air. Near the surface, water vapor makes up about 1% of the air, whereas at the tropopause the concentration is just a few parts per million (and the air is much less dense). this invention provides a way of operating a spectroscopic sensor so as to maximize the dynamic range, by providing means for measuring optically thick signals. The figure shows the calculated transmission for one spectrally-resolved feature of methane. At high concentrations, the transmitted light near the center of the methane peak is about 0%. The concentration of methane can still be measured accurately by determining the spectral width of the peak. The combination of wavelength modulation at low concentrations, direct absorption at moderate concentrations, and width measurements at high concentrations results in a very wide dynamic range without adding much to the cost of the hardware.
Contact Information
e-mail info@swsciences.com