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6 Measurements with the meter
The basic configuration of the MOIST 350 consists of the handheld and the sensing
heads MOIST-PM V2 and MOIST-R1M V2(see title).
For doing measurements some special features of the microwave method have to be
kept in mind, which are described in the following chapter.
6.1 Basics of Dielectric Moisture Measurements
The microwave method is a dielectric moisture measurement method.
Dielectric measurement methods are based on the special physical properties of water.
Water is a polar molecule, i.e. the molecule doesn’t appear electrically neutral when an
electric field is applied to it. That’s why the water molecule will orientate in a preferred
direction given by the electric field - it is polarizable. If an alternating electromagnetic
field is applied, then the water molecule will start rotating with the frequency of the field
(orientation polarization). This effect is described macroscopically by the physical
property Dielectric Constant or permittivity.
The dielectric effect of water is very strong, it’s permittivity is about 80. The permittivity
of the most solids (for instance building materials) is much smaller, it ranges between 2
and 10 and mainly between 3 and 6.
Therefore the difference between the permittivity of water and the permittivity of the
solids is measured. Because of the great difference of these values even small amounts
of water can be detected well.
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