The CRH in the term “CRH method” stands for corresponding relative (air) humidiy. It describes the equilibrium moisture content, which is achieved when, in addition to air, a sample containing water is stored in a closed system.
Instead of the term “CRH method” other, more known terms like “measurement of the water activity” and “the determination of a material’s climate” can be used.
The CRH method allows for the determination of the state of moisture of an arbitrary sample through the measurement of the state of equilibrium of the air in a 3-material system. It is therefore an indirect system for the determination of mositure. the system is strongly temperature-dependant and salt loads in porous water can lead to unspecific measurement results.
In its state of equilibrium and at a constant temperature the relative humidity will not change anymore. The mass transger out of the sample into the air and out of the air into the sample occurs, just like the chemical reaction of the carbide method in its state of equilibrium, equally fast.