Abstract
An apparatus is described for following in the factory the progress of a vapour-phase reaction by absorptiometric measurements. The apparatus determines the instantaneous value of the component in a pipe, operates alarm relays if it departs from preselected values, and may control valves. The types of apparatus described are accurate, simple and robust, with electronic amplifiers of rugged type. The detectors used are photo-multiplier cells with chopped beams and electronic a.c. amplifiers; the chopping may be by a sector disc but we have preferred a mercury vapour source modulated at mains frequency. Compensating beam layout of the apparatus is used, and the amplifier has sufficient feedback to secure stability while having enough stages to secure high gain. Standardisation of the amplifier is by two built-in filters giving selected output values. As examples of the application of the apparatus are the estimation of chlorine from 10 −5 to 10 −1, of NO 2 of sulphuric anhydride, of humidity in the range 10–250 mg m 3 .
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