Performance of Remote Moisture Sensing Devices

Unitized electrical resistance, wood-element, moisture sensing probes have been developed after designs by Talbot, Delmhorst, and Duff which when inserted and sealed in holes bored in drying lumber respond to the moisture gradients which occur in kiln-drying atmospheres. The sensors consist of hard maple (Acer saccharum) elements 0.07 inches square and 0.75 inches along the grain with electrodes on opposing faces consisting of epoxy silver adhesive to which leads are bonded using the same adhesive. One of the leads is fused to a constantan lead to provide a thermocouple for temperature readings at the point of moisture measurement. The three leads and the end of the attached wood element are rigidly enclosed in a shaft produced by heat shrinkable polyolefin tubing. A threaded teflon cap with 0-rings is provided for an effective seal of the hole into which the probe is inserted. Sensors can be calibrated to read directly on commercial resistance-type moisture meters or to the particular wood species being dried by adjusting the electrical resistance of the wood element by shortening it until direct reading is achieved. Trial runs in 8/4 red oak (Quercus rubra) demonstrated that the sensors are durable and sensitive to moisture change of less than 1 percent of fiber saturation point and below. The system of bored holes required for the sensors does not appear to affect the normal drying moisture gradient. As a consequence, the true moisture gradient can be sensed by the probes.

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