Measuring low levels of methane in carbon dioxide
First Claim
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1. A method of detecting trace amounts of methane in carbon dioxide backgrounds, comprising:
- directing a beam of light at a selected wavelength through a gas mixture comprising carbon dioxide and methane, the selected wavelength coinciding with a methane absorption feature that is resolvable from an absorption background due to carbon dioxide;
quantifying an absorption at the selected wavelength in the gas mixture; and
determining a methane concentration in the gas mixture based on the quantified absorption.
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Abstract
Low concentrations of methane in a gas mixture containing a substantial concentration of carbon dioxide can be detected and quantified using absorption spectroscopy in the infrared spectral region. Absorption spectra can recorded using tunable diode lasers as the light source. Modulation of the laser signal and demodulation of the resultant detector response yields dependable measurements that may be conducted with very little maintenance in demanding environments.
20 Citations
20 Claims
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1. A method of detecting trace amounts of methane in carbon dioxide backgrounds, comprising:
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directing a beam of light at a selected wavelength through a gas mixture comprising carbon dioxide and methane, the selected wavelength coinciding with a methane absorption feature that is resolvable from an absorption background due to carbon dioxide;
quantifying an absorption at the selected wavelength in the gas mixture; and
determining a methane concentration in the gas mixture based on the quantified absorption. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus comprising:
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a laser light source that emits at a selected wavelength that coincides with a methane absorption feature that is resolvable from an absorption background due to carbon dioxide;
a sample cell to contain a gas mixture containing methane and carbon dioxide with a methane concentration of less than or equal to approximately 5%, the sample cell providing a path length through the gas mixture of less than or equal to approximately 50 cm;
a photodetector positioned to quantify an intensity of light traversing the path length and to output a direct current data signal based on the quantified intensity; and
a microprocessor configured to receive and interpret the direct current signal from the photodetector and to determine the methane concentration in the gas mixture based on the direct current data signal and a calibration function. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of detecting trace amounts of methane in carbon dioxide backgrounds, comprising:
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directing a beam of light at a wavelength in the range of approximately 1630 nm to 100 nm through a gas mixture comprising carbon dioxide and less than approximately 5% methane, the selected wavelength coinciding with a methane absorption feature that is resolvable from an absorption background due to carbon dioxide, the beam of light being provided by a tunable diode laser;
quantifying an absorption at the selected wavelength in the gas mixture over a path length of less than or equal to approximately 50 cm; and
determining a methane concentration in the gas mixture based on the quantified absorption and a calibration function.
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Specification