A Statistical Approach for Determining the Impact of Sensor Orientation and Electrode Type on Moisture Content Measurements in Eastern White Pine

Abstract

As buildings become more airtight and insulated, the movement and accumulation of moisture within building envelopes become paramount in determining its resiliency.Current methods for quantifying the moisture content (MC) of wood species involve the measurement of electrical resistance between two installed electrodes and the use of existing empirical correlations to evaluate the MC. However, these correlations do not adequately consider the impact of sensor orientation and electrode type within wall assemblies. The aim of this study was to statistically examine the impact of sensor orientation and electrode geometry on MC measurements in 126 eastern white pine samples with electrodes placed along and across the grains of the wood using six different fasteners. Samples were placed in a controlled environmental chamber until steady state was achieved at three relative humidity (RH) levels. Oven-dry MC measurements were taken and electrical resistances were measured in both directions as samples reached steady state at each RH level (73.3%, 85%, and 92.5%) at temperatures ranging from -10℃ to 40℃. Based on the homogeneous nature observed from statistical t-tests, it was determined that sensor orientation does not have a significant impact on MC measurements (p>0.05) and therefore does not need to be considered. Additional t-tests and multivariate regression analyses using Pfaff and Garrahan's empirical MC equation showed that fasteners similar in geometry to 2.1mm stainless steel nails require a unique set of regression coefficients (p<0.05) to minimize overall 𝑅𝑀𝑆𝐸 from 1.81%MC to 0.79%MC. A different and more general set of regression coefficients was developed for the other 5 fasteners to minimize the overall 𝑅𝑀𝑆𝐸 from 1.15%MC to 0.85%MC. When using electrodes and regression coefficients that are incompatible, errors associated with MC can reach up to ±2% MC.