The present invention relates to photoelectric gas analysis under utilization of the specific absorption of radiation by a gas upon being traversed by such radiation.
U.S. Pat. No. 3,694,086 is representative of this field of art; it describes a correlation spectrometer for measuring the concentration of certain gases such as SO.sub.2, NO, NO.sub.2, and others. The equipment disclosed in that patent includes a source of ultraviolet light. A transducer introduces cyclically a dual-filter into the light path so that, alternatingly, two wavelengths are transmitted and pass through the gas; one of the wavelengths is an absorption line of the component to be detected, the other wavelength is not. The intensities of the radiation at the two wavelengths are detected photoelectrically and processed to obtain a measuring result.
U.S. Pat. No. 3,947,685 discloses measuring the NO content in a carrier using a particular hollow cathode tube emitting radiation which is alternatingly intercepted by two cuvettes, one containing NO, the other one air. Thus, the filter containing NO also preabsorbs some of the radiation to which the component to be detected is specifically responsive. Moreover, the source of radiation for this equipment is specifically constructed to emit radiation by exciting NO molecules; it is, thus, specific as to the gas concentration to be detected. See also U.S. Pat. No. 4,176,963.
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