Abstract: A gas analyzer is described comprising a sample cell for containing a gas mixture to be analyzed, a source for producing and directing infrared energy through the sample cell, a rotary filter wheel having at least one filter thereon for passing infrared energy limited to a wavelength band within the characteristic absorption band of a predetermined gas and having a dark level region substantially opaque to infrared energy, a drive for supporting and rotating the filter wheel to successively interpose the filter and the dark level region between the source and the sample cell in the path of the infrared energy directed by the source, a detector for detecting infrared energy passing through the sample cell and producing an electrical signal representative thereof, and a signal processor connected to the detector for producing an output indicating the concentration of the predetermined gas in the sample cell by comparing the electrical signals produced by the detector with the filter positioned in the infrared e