Effect of Temperature on Reading of Electric Moisture Meters

Temperature effects on readings of electric moisture meters were obtained on two softwoods and two hardwoods for a range from 0? to 200?F, and for a moisture range from 8 to 20 percent. The data for the resistance meter essentially confirmed previous results; the electrical conductance of wood increases with both increasing temperature and moisture content, and existing charts for temperature correction of resistance-type meters appear valid. Data for the capacitive-admittance meter were similar in form to those for the resistance-type meter. Capacitance admittance, essentially a measure of dielectric constant when the loss tangent is not excessive, increased with both increasing temperature and moisture content with an apparent positive interaction. Data from the power-loss meter were more complex, showing maximum and minimum values at certain combinations of temperature and moisture content. Power-loss data were similar to internal friction data and suggest that the loss mechanisms are analogous. Temperature had no measurable effect on the calibration of the resistance meter itself, but both radio-frequency meters showed zero offset and calibration changes when cooled below room temperature. Charts for approximate temperature correction of the readings of radio-frequency moisture meters are given.

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