Objects to be measured electrically turn into electric insulator or semiconductor. They are shown equivalently as a parallel circuit of resistance R and electric capacity C.Moisture contents are measured utilizing these electrical characteristics.
The electric moisture meters are classified into two types, one utilizes the change of resistance R and the other utilizes the change of electric capacity C.As the relation between moisture and resistance or capacity is different by a kind of materials, several kinds of meters are provided for each object to be measured such as for wood, paper, and mortar, or the meter which is applicable to the object to be measured by changing a type of the probe.
Electric resistance type moisture meters utilize the electric character of the measuring objects sensitively reacting to moisture contents and the reacting relations between them do not correspond with in a full one-on-one basis.
It is necessary to adjust, rectify, compensate for measuring methods and results or avoid critical places for the measurements when tissues and compositions of objects are different even with the same materials, when they are deteriorated or contaminated, when specially processed or liquid treatment is made.
As for compensations of measuring results, the moisture measurement method by drying method is generally applied as standard.