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Abstract

An apparatus and method for open-path gas detection. The apparatus includes a radiation source and first and second radiation detectors sensitive to radiation in first and second spectral bands. The long cut-off wavelength of the second spectral band is longer than the long cut-off wavelength of the first spectral band, and the short cut-off wavelength of the second spectral band is shorter than the short cut-off wavelength of the short spectral band, such that the second spectral band is wider than and completely overlaps the first spectral band. Radiation from the radiation source passes through the area to be checked for gas, and is partially absorbed if gas is present. The path between the radiation source and the first and second radiation detectors need not be enclosed, and may exceed 100 meters in length. A processor compares intensity signals from the radiation detectors with a threshold value, and generates an output signal indicating a presence of gas based on the comparison. The method includes the steps of passing radiation through an area, and sensing radiation that has passed through the area within first and second spectral bands, wherein the long cut-off wavelength of the second spectral band is longer than the long cut-off wavelength of the first spectral band, and the short cut-off wavelength of the second spectral band is shorter than the short cut-off wavelength of the short spectral band. The intensities in the spectral bands are compared with a threshold value, and the presence of gas is indicated based on the comparison.

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