Resistance Moisture Meter Correction Factors for Western Softwood Species

Species correction factors for the standard Delmhorst resistance moisture meter were determined for the following species: Pinus monticola, Pinus contorta, Picea sitchensis, Picea glauca, Pseudotsuga menziesii (Mirb.) Franco, Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco, Larix occidentalis, Abies amabilis, Tsuga heterophylla, Chamaecyparis nootkatensis, and Thuja plicata. Green boards were either air-dried or kiln-dried using a conventional industrial schedule or constant high-temperature conditions. After drying, 28 replicates of each drying schedule were put into a constant environment designed to achieve an equilibrium moisture content (EMC) of 6 percent. After several months of exposure, the MC of the specimens was determined by a standard Delmhorst moisture meter, equipped with four 5/16- inch-long needles; and the samples were weighed. The specimens were similarly exposed to four additional EMC conditions, namely, 9, 12, 15, and 18 percent–9 percent EMC with 73?F temperature and 50.5 percent PH; 12 percent EMC with 70?F temperature and 64 percent RH; 15 percent EMC with 86?F temperature and 78 percent RH, and 18 percent EMC with 75?F temperature and 82 percent RR. Finally all specimens were ovendried and MC calculated for each exposure condition. The individual EMCs obtained by ovendrying and the corresponding resistance MC readings under the five different environments were tabulated. Linear regressions of resistance moisture meter readings on oven-dried MCs gave the species corrections, which are algebraically additive to resistance meter readings. The magnitude of the correction factors generally increased with MC, and ranged from -2.0 (western red cedar) to 2.4 (western white spruce and western hemlock sapwood). The upper and lower 95 percent inverse fiducial limits were calculated for each combination of species and equilibrium condition; these limits ranged from ?0.02 to ?0.26. Their narrow limits indicate that the different drying schedules employed prior to conditioning had no appreciable effect on the correction factors obtained.

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