GB922128A - Improvements in and relating to infra-red gas analysers - Google Patents

Abstract

922,128. Infra-red gas analysers. Sir HOWARD GRUBB PARSONS & CO. Ltd. June 15, 1961 [June 15, 1960], No. 21078/60. Class 40 (3). An infra-red gas analyser for the analysis of two or more components in a gas mixture comprises two separate radiation paths 2, 3, means in one path 2 for receiving the mixture, detection means 4 sensitive to wavelengths capable of being absorbed by each component to be determined, the detection means producing a signal whose magnitude is a measure of the difference in energy reaching it over the two paths, and wavelength selection means comprising interference filters, each transmitting a narrow wavelength band coincident with a region of absorption by one component, the filters 8a being movable one at a time into at least the radiation path 2 containing the test mixture. Radiation from each of two sources 1a and 1b is interrupted simultaneously by a chopper 7, that from one 1a being passed through the test mixture 2 and that from the other 1b being passed through a comparison gas 3 exhibiting constant absorption properties. Unequal absorption in the two paths results in a pressure difference between two chambers 4a and 4b of the detector 4, the chambers being filled with a gas exhibiting similar absorption properties to the test mixture, this difference producing deflection of a diaphragm 5 relative to a fixed electrode 6 to produce a pulsating signal whose magnitude is indicative of the relative absorption. Interference filters 8a and 8b are mounted, Fig. 2, to be rotated respectively into the radiation paths to select in turn each wavelength range appropriate to the components being analysed. The filters for the two paths may be mounted in a common carrier which may be rotated or moved linearly, and the movement may be remotely controlled. Instead of identical filters in the two paths, one or both may incorporate an adjustable optical trimmer such as a screw projecting into the radiation path and these screws may be adjusted for equal path energy content when no sample is present. An attenuator may be used in one path in place of a filter.