A self-contained hydrocarbon dew point analyser that combines a hydrocarbon dew point cell and water dew point measurement in a single compact and lightweight explosion proof, or EExd, enclosure, requiring only mains power to operate, is now available.
Michell Instruments, locally represented by Instrotech, offers the Condumax II On-Line that uses the Dark Spot measurement principle, which is a patented chilled mirror optical measurement technique that is said to be radically different to that of any other instrument.
Sensitivity of better than 1 ppm molar (1 mg/m3) of condensed hydrocarbons enables the analyser to detect the almost invisible films of condensate that are characteristic of hydrocarbon gases at dew point, owing to their low surface tension and colourless appearance, explains the company. The result is seen as a breakthrough in accuracy and repeatability.
The optical sensor comprises an acid etched, semi-matt stainless-steel mirror surface with a central conical-shaped depression, which is chilled during a measurement cycle. Collimated visible red light is focused onto the central region of the optical surface. In dry conditions, the incident light beam is dispersed by the matt surface providing a base signal to the optical detector. During a measurement cycle, hydrocarbon condensate is formed on the optical surface and it becomes reflective, owing to the low surface tension of the condensate. An annular ring of light forms around the detector and there is a dramatic reduction in the scattered light intensity within the central Dark Spot region.
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