Portable dew point meter for compressed air Model ATS 301D Applied Techno Systems offer portable microcontroller based dew point meter for Compressed air having dew point range -80 to +30 Deg C Dew point is defined as the temperature at which the water vapor pressure of a gas equals the saturated water vapor pressure. It is therefore the temperature at which condensation "just begins" to occur if a gas is cooled. Dew point is a fundamental unit and directly equivalent to water vapor pressure or parts per million. It is a very convenient measure of actual water content of a gas because it is not a function of temperature in the same way relative humidity