
As with dissolving solids in a liquid, a gas can only hold a certain amount of dissolved moisture before it starts to condense back to liquid phase. Relative humidity is a measure of the humidity in terms of its saturation point.

There is always a level of humidity in the air around us, but when it comes to industrial processes, the levels of humidity often need to be controlled. Humidity is simply moisture that is dissolved in a gas. What are the differences between humidity, dew point and relative humidity? As well as the term ‘hygrometer’ it may also be called a: Hygrometry is the measurement of the moisture content of gases, and a hygrometer senses, measures and outputs or displays the relative or absolute humidity in the gas.

(If you want to find out about meteorological applications for dew point measurements, here is a short explanation from the UK Met Office.) It’s a common parameter in meteorology, hence the name ‘dew point’ but in this article we are going to look at why it’s important to a wide variety of industrial processes. Where the condensate is ice, this is known as the frost point.’ The NPL defines dew point as: ‘The temperature at which dew, or condensation, forms as you cool a gas.
