Humidity measurement technology
Definitions & Terms
Relative humidity has always been an important factor for the condition and health of humans, animals, plants and objects.
We experience relative humidity ourselves on a daily basis, often unknowingly. For example the morning dew is the humidity of the night air, which condenses in the cooler morning hours.We apply its laws, for instance when we have a sauna, we increase the temperature of the air so much that the air absorbs a lot of moisture. We recognize the high influence of humidity upon our well-being. Everyone is familiar with the sensation where the mucous membrane of the nose dries up during the heating period during the winter, placing everyone at risk of catching viral infections or the unpleasant sultry feeling that we experience in the prevailing high humidity during the summer.
Relative humidity plays a major role, not only in what we perceive to be comfortable but also for the condition of many things. In many production processes, goods require the correct level of relative humidity as otherwise they lose their properties. We are thinking for example here of paper which is hygroscopic and which causes problems if you try to print on it under incorrect humidity conditions, or storing fruit and vegetables which start to shrink and ripen too early if stored in the wrong humidity conditions, of computer systems which switch off, if the air around them is too dry or too humid, of sausage and cheese, of storing steel, preserving steel armour, drying of tobacco, the list is endless.
Measuring principles
Galltec+Mela are manufacturer of humidity measurement products based on two different basic measurement principles: Hygrometric and capacitive.
More information
Definitions, terms, measuring methods
Maintenance instructions
Absorption Principle
Humidity sensing elements, Modules
Relative humidity
Relative humidity is a “dimensionless quantity”, it is a ratio. You will often find the description %RH. A figure on its own, e.g. 50 %, often makes no sense, as other quantities are also given in %, such as 50 % actuating variable. To avoid any misunderstandings, Galltec+Mela retain the description 50 % RH.
Relative humidity is used to identify the level of humidity in the air and is determined as follows:
The dew-point temperature is the temperature at which the air is saturated with water vapour at constant air pressure. The prevalent water vapour partial pressure is then equal to the water vapour saturation pressure.
The dew-point temperature and thus the water vapour saturation pressure of the humid air are attained for example by cooling the humid air at a temperature t without changing pressure or humidity, until condensation of the water vapour occurs at the dew-point temperature td. The dew-point temperature is equal to the water vapour saturation temperature.
The dew-point temperature difference is the difference between the temperature and the dew-point temperature of the humid air.
The Mollier-hx-diagram
(1923 Richard Mollier)
