Relative humidity (RH) is defined as the ratio of the water vapor pressure or water vapor content to the saturation vapor pressure or the maximum vapor content at the temperature of the air or gas. The saturation vapor pressure in the air varies with air temperature, the higher the temperature, the more water vapor it can hold. When saturated the relative humidity in the air is 100 %RH.

Vaisala's wide variety of relative humidity measurement instruments cover all the applications from ventilation to process control in demanding explosive areas.

Dewpoint is the temperature at which air becomes saturated with water and begins to condense - forming dew. Therefore at 100 % relative humidity the ambient or process temperature equals the dewpoint temperature. The more negative the dewpoint temperature is from the ambient temperature, the smaller is the risk of condensation and the drier the gas or air stream.

Vaisala's dewpoint products provide solutions for humidity measurement problems in dry conditions.