| 摘要 |
979, 850. Infra-red gas &c. analysers. OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AEROSPATIALES. May 26, 1961 [June 3, 1960], No. 19152/61. Heading G1A. In an infra-red analyser radiation from a source 1, Fig. 1, is passed through two chambers 2, 3, the first containing the fluid (which may be in motion) whose concentration is to be determined from the extent to which it absorbs radiation, and the second containing a reference fluid, and the emergent radiation from the two is directed alternately by a rotating shutter 6 on to a detector 7 comprising two radiation sensitive elements so that the concentration may be indicated at 14 in terms of the difference between, or ratio of, the alternating signal from the two elements. In a first embodiment the elements are leadsulphide photo-electric cells 10, 12, in front of which are disposed interference type filters 9, 11, respectively. The filter 9 has a passband including wavelengths lying within the absorption spectrum of the test fluid, whilst the filter 11 has a passband which differs from that of filter 9 although it may embrace it. A semi-transparent mirror 8 8 transmits some of the radiation incident upon the detector to the photo-cell 11 and transmits the remainder to the photo-cell 10, the characteristics of the mirror and filters being such that the intensities of illumination of the two photocells is approximately equal when there is no selective absorbtion in either of the chambers 2 and 3. This arrangement is stated to result in there being an indication of absorption on the instrument 14 due to an alternating differential output from the photo-cells only when energy is absorbed in the chamber 2 within the passband of the filter 9, so obviating errors due to variations affecting both chambers. In another embodiment detector of the type disclosed in Specification 849,831 is utilized in which two successive layers of gas 15, 16, Fig. 3, are exposed to the radiation and the differential pressure produced is measured by a diaphragm capacitor 17. The gas 15 absorbs radiation within the absorption spectrum of the substance to be investigated and the gas 16 exhibits absorption outside this range. In either embodiment two sources may be used, each irradiating one of two separate chambers. |
