JPS6423142A - Detector for sulfurous acid gas - Google Patents

Abstract

PURPOSE:To enhance the sensitivity of an SO2 detector by suppressing the standing waves of the light generated in a sensor optical part. CONSTITUTION:The exit light of a semiconductor laser element 3 is branched by a beam splitter 4. One thereof constitutes the measuring optical path which is multiple-reflected in a long optical path cell 2. The other constitutes the reference optical path which passes a reference gas cell 1. The reference optical path is subjected to absorption of SO2 in the cell 1 contg. gaseous SO2 and is photodetected 5. On the other hand, the laser light subjected to the absorption of the gaseous SO2 and steam in the cell 2 is photodetected 6. The signals detected by the detectors 5, 6 are passed through signal detecting circuits 7, 8 by which the signals are made into second order differentiation signals. These signals are converted to the concn. value of the gaseous SO2. The standing waves of the light are generated in the container for housing the element 3 and the independent window bodies of the detectors 5, 6. The surfaces of the windows are, thereupon, inclined at a prescribed angle in the light transmission direction in such a manner that the transmitted light and the reflected light in the window parts do not overlap on each other on the detecting element. In addition, the sections of the windows are made into a wedge shape to remove the overlap of the transmitted light and the reflected light and to suppress the standing waves of the light, by which the sensitivity of the device is enhanced.