Michell Instruments has introduced the S8000RS Precision Chilled Mirror Hygrometer. It measures dew points down to -90°C (0.1ppmv) with an accuracy of ±0.1°C. However, no additional external cooling equipment is needed to accurately reach these dry dew points.
Designed to fit into a standard 19″ rack, the hygrometer is compact and convenient because it does not need extra equipment to work. According to the company, its compact design was made possible due to a new optical system that detects very small changes in moisture condensed on the mirror surface, leading to high sensitivity and fast response when measuring low dew points.
Although referred to as ‘dew-point temperature’, chilled mirror hygrometers most often measure the frost point because the temperatures are below freezing. However, in some conditions, liquid water can exist as ‘super-cooled water’ in temperatures as low as -40°C. Because the difference in condensing temperature between water and ice can be as much as 10 per cent of the reading, it is essential to know which phase you are measuring.
This hygrometer uses Frost Assurance Technology (FAsT) to ensure that ice, not liquid water, is present on the mirror surface at low temperatures to ensure that measurements are always a known quantity.