Artifacts in electrical measurements on wood caused by non-uniform moisture distributions

Abstract

This paper examines how the moisture conditioning method affects the electrical conductance of wood. A widely used dataset was acquired by Stamm in 1929 who used a method of conditioning where water-saturated wood specimens were partially dried, sealed and left for a period of time for moisture to be redistributed before the electrical conductance was measured. However, more recent measurements combined conditioning above saturated salt solutions and pressure plate/pressure membrane techniques to obtain equilibrium moisture contents at constant relative humidity levels in the full moisture range. In this paper, the electrical conductance as a function of moisture content was compared for these two conditioning methods. When the specimens were conditioned to constant relative humidity levels, the data obeyed a percolation model better than when the conditioning procedure by Stamm was used. This was attributed to that Stamm’s method gives moisture gradients through the specimen because of sorption hysteresis effects, even though the wood is conditioned to a steady-state moisture content. Equilibration to constant relative humidity levels thus provided more well-defined moisture states and that the data followed a percolation model indicates that the mechanism of electrical conduction in wood does not change, even at high moisture contents.

Wood Modification as a Tool to Understand Moisture in Wood

“…Conditioning, especially at high moisture contents is, however, often done by drying samples down to a specific moisture content. This introduces moisture gradients within the sample that can make the interpretation of results challenging due to non-uniform moisture distributions [60]. Increased knowledge on the location and state of water at different water potentials therefore requires careful conditioning procedures in order to get well-defined results.…”

Calibration of Electrical Resistance to Moisture Content for Beech Laminated Veneer Lumber “BauBuche S” and “BauBuche Q”

“…A recent study by Fredriksson et al [31] showed that moisture gradients in wood can have an impact on resistance measurements. In real timber structures, moisture gradients usually predominate over steady-state moisture conditions.…”

Resistividad eléctrica de la madera de Pinus pseudostrobus, Tabebuia rosea y Quercus scytophylla

“…El mecanismo de conducción eléctrica en la madera depende de la presencia de iones, como portadores de carga en la pared celular, y de las propiedades de porosidad del plano leñoso, lo que resulta en un mecanismo de percolación a través del cual se produce el movimiento de iones (Zelinka, et al, 2016;Fredriksson, et al, 2021). Así, la estructura anatómica (Jiang, et al, 2003) y su composición química (Jakes, et al, 2013) Una de las aplicaciones más importantes de la caracterización de las propiedades de resistencia eléctrica de la madera es la correlación con su contenido de humedad (Fernández-Golfín, et al, 2012).…”