Method of Measuring Dew point Measurements
It is defined as the temperature at which air attains saturation and a further addition of water vapour leads to dew formation because of condensation of water vapour. It is rarely used to indicate the moisture content of the air. The temperature recorded in this case is dry bulb temperature. At dew point, dry bulb and wet bulb temperature are same.
Dew point products use chilled mirror hygrometers. These can measure dew/frost points from -80 degree C to 85 degree C that is obtained by cooling a solid surface usually a mirror, until condensation occurs on the surface. High accuracy (±0.15 degree C) platinum RTD is embedded in the mirror surface to measure the reading. Various methods used to cool the mirror include ice, refrigerants (freon), thermoelectric cooling etc. These are often used as a secondary standard to calibrate other humidity transducers.