The Influence of Specimen Size and Distance to a Surface on Resistive Moisture Content Measurements in Wood

The moisture content of wood is commonly determined by measuring the electrical resistance between two electrodes inserted in the wood. However, problems using this method close to wood surfaces were reported in a previous study. In the present study, the effect of the distance to a surface and the specimen size on the measured electrical resistance was studied analytically as follows. The two electrodes create an electrical potential in the wood specimen. The boundary condition for the electrical potential is that the electrical current across all specimen surfaces is zero, which is achieved by using a suitable array of mirror sources. The analytical solution for the electrical potential was used to analyse the influence of the distance from the electrodes to the specimen surface as well as the size of the specimen. In addition, the error in moisture content was evaluated. The effect of the distance to a surface and the specimen size depended on the equivalent radius of the electrodes; if large electrodes are used in small specimens or close to surfaces, there is a risk that a higher resistance is measured which results in slightly lower measured moisture content than the actual moisture content of the specimen.