Michell Instruments’ S8000 Integrale cooled mirror hygrometer is able to cope with sample gas at pressures of up to 17 barg. This means a reduced response time which can help save users time and money in dry applications – such as compressed air manufacture – where low dew-points are reached.

Pressurising the sample speeds up the response time because the gas will have a higher dew point than the same sample at atmospheric pressure. This is because the water molecules are squeezed closer together under pressure making the sample "wetter" than it would be at atmospheric pressure. For example, a pressure dew point of -65°C at 17barg is equivalent to an atmospheric dew point of -100°C. With the higher dew point under pressure, the S8000 is able to reach the temperature and stabilise much fast than with the lower atmospheric dew point.

The response speed of the instrument has been further enhanced with updates to the S8000 firmware to allow the tracking of any minute dew point changes in the sample gas. All this is good news for manufacturers of compressed air or expensive gases, as increased response time will allow them to react faster to changes and reduce wastage and down-time.

Operating at pressure has the additional benefit of removing the need to reduce pressure on the inlet of the chilled mirror device. The sampling system is accordingly greatly simplified by eradicating potential uncertainties associated with the use of pressure reducing devices which are prone to water vapour contamination. This is of particular benefit to compressed air systems.