An Introduction to Humidity Measurement

Relative Humidity
Relative Humidity or RH is defined as the amount of water vapour held in the air compared to the amount that the air can hold at any given temperature. The higher the temperature, the more water vapour can be held in a given volume of air.

The %RH is the ratio of water vapour present in the air relative to the amount required to reach saturation or for condensation to begin to form at the current temperature.

ATP has an extensive range of hygrometers to allow the measurement of relative humidity in commercial applications.

Dew Point Calculation

Dew Point is defined by a reference temperature at which condensation (dew) will form given the current %RH measured value

As an example, the dew point temperature of air containing 10 grams per cubic metre of water vapour is about 11°C. If air at this temperature contained only 5 grams per cubic metre of water vapour, its relative humidity would be 50%.
Click on image above to view diagram in more detail.

ATP has a range of dew point hygrometers for measurement and testing applications.