Although the drying process can improve the overall quality and usefulness of forest products, if drying is not carefully controlled, drying loss can be substantial. As most drying defects occur when the lumber moisture content is above fiber saturation point (FSP), measurement of moisture content (MC) above FSP is critically important. In this study, a technique was developed which permits use of an electrical resistance moisture meter RDX-1 (Delmhorst Instrument Company) to measure MCs of red oak and yellow-poplar during drying when MC is above FSP. The Lignomat in-kiln probe electrode was used throughout experiments. Two experiments were conducted. The first dealt with developing a two-point technique to measure MC above FSP. The other evaluated the effect of the moisture gradient on the MC reading from the meter. During the drying, pin electrode also was used when oven-dry MC was about 40% in order to compare the MC readings by the pin electrode and the probe electrode.

The experimental results show the correlation between the MC readings and oven-dry MC of the sample is quite high during drying; the correlation of each sample is higher than 0.9. Based on this relationship, two-point technique of measuring MC above FSP was developed. This technique can predict MC above FSP of red oak within 5%, and the MC of yellow-poplar within 10%. From the experiment, it was found, when MC is above FSP, MC readings measured by probe electrodes are significantly different from those measured by pin electrodes. It was also found that the moisture gradient affects the MC readings dramatically. The depths of probes inserted into the boards are an important parameter for measuring MC. Different depths yield different MC readings.