At one end of the spectrum is the classic Speedy Moisture Tester where
Then there are instruments that use absorption of electromagnetic frequencies to detect and quantify moisture. These work using frequencies in the near infrared microwave and radio spectra. Pretty sophisticated algorithms are needed to get the moisture measurement job done with some of these. The instruments that do this are above the $12,000 price range.
There is what I consider the "other side of the moisture measurement world". Here we measure how moisture travels between the environment and a material and how it travels between the material and the environment. I call this the "World of Sorption". In fact, there is a water sorption group on LinkedIn devoted to this type of moisture measurement.
The "sorption universe" is involved in measuring how much moisture is yielded into a controlled environment (sometimes referred to as water activity) and how much water is adsorbed from an environment of controlled humidity.
Devices called water activity meters are used to determine this moisture yield characteristic. This is done by putting a sample in a closed chamber and measuring the level of relative humidity created by the moisture leaving the material.
When water activity is generated for varying environmental conditions and at different water content levels, the relationship of moisture content and water activity can be developed and presented as Sorption Isotherms.
To measure the other direction (adsorption of water instead of shedding water), a technique known as Dynamic Vapor Sorption can be used. To give a simplified picture of this technique, imagine that
Hope this little ramble contained some useful insight. Please share it with associates who you think might enjoy it.
I remain mystified, as usual, by the consequences of looking into what seems like a simple question.
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By Art Gatenby