Tamme. V *, Muiste, P., Padari, A. and Tamme, H. 2014. Modelling of Resistance-Type Wood Moisture Meters for Three Deciduous Tree Species (Black Alder, Birch, Aspen) in Moisture Contents Above Fibre Saturation Point. Baltic Forestry 20(1): 157-166.

For fast detection of wood moisture content (MC), handheld resistance-type and capacitance-type electrical moisture meters are widely used. In moisture contents above the fibre saturation point (FSP), the measuring accuracy and precision of resistance-type moisture meters starts to progressively decrease as the wood MC increases. The aim of this research was to quantitatively explore this well-known qualitative trend. Three different resistance-type wood moisture meters from leading manufacturers were compared. The display readings of the moisture meters were compared by using the absolute MCs determined for relevant specimens with the oven-dry method. The specimens with the dimensions of 100x60x60 mm (length x width x thickness) were made of three different tree species (black alder, birch, aspen); a total of 60 specimens per each tree species were used. The specimens were dried in a climatic chamber under equal conditions (32°C and 98% RH) until the desired MC was achieved. All wood MC measurements were conducted at a room temperature of 20°C.

Modelling of experiment data confirmed the progressive increase in the absolute error in a single measurement of wood MC with resistance-type moisture meters as the average absolute MC rose. Based on the model, the absolute error on the same confidence level (95%) and for the average MC of 27% was ± 3.9% MC, for the average MC of 60% it was ± 10% MC, and for the average MC of 97 % the absolute error was ± 17.5% MC. The best prediction error in wood average MC predicted on the basis of the same model was ± 1.12% MC. The same model was used to predict the resolution of resistance-type moisture meters for the above-mentioned average MCs, which was found to be approximately 1% MC.

Key words: wood drying, wood moisture meter, above FSP.