Abstract: Very generally, the gas analyzer of the invention includes a source of infrared energy, a sample cell for containing an analyte gas mixture positioned in the path of infrared energy, and a monochrometer including a movable diffraction grating for producing a beam of infrared energy wherein the constituent wavelengths are spetrally separated. The device also includes a wide band interference filter for transmitting a predetermined wavelength band spanning the characteristic absorption wavelength of each of a plurality of constituent gases in the analyte gas mixture. A detector positioned to receive radiation passing through the filter produces an electrical response related to the infrared energy impinging thereon. The monochrometer includes provision for moving the diffraction grating to sequentially cause infrared energy of different wavelengths to impinge upon the detector, and for intermittently causing infrared energy directed toward the detector from the source to be blocked by the interference filter.