| 摘要 |
The invention relates to apparatus for open-path gas monitoring and is particularly concerned with measuring the opacity of stack gases. Single and double pass systems to provide an optical across the stack, are known, but to provide meaningful data, gain compensation is required to deal with temperature variations and the possibility of ageing of electronic components. The object of the present invention is to provide an instrument that meets the above requirement but without moving components, which objective is met by a construction comprising a transceiver unit adapted to be mounted on one side of the optical path; a passive reflector adapted to be mounted on the other side of the path; and electronic control circuitry, the transceiver unit comprising: (i) first and second light detectors; (ii) first light source capable of projecting a beam of light along the optical path (iii) second light source capable of flooding the first and second detectors with light; and (iv) means to alternate activation of the first and second light sources at a predetermined frequency.
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