Moisture content measurement in the wood industry

Abstract: In the wood industry, determination of the moisture content (mc) with a high accuracy is of great importance. The green mc is important for optimisation of the wood drying process at sawmills, whereas the mc of dried boards is of interest for the further processing and final use of the boards. In the first publication in this thesis, which is a technical report written in Swedish, different measuring techniques with their own pros and cons are discussed. A total of 13 different measurement principles are discussed, focusing on the ability to measure mc in the range of 7-18%. The result suggests that mc-meters that use electromagnetic waves in the radio- and microwave ranges have the greatest potential to become the next generation mc-meters for dried boards. The second publication, which is presented in this thesis, investigates the possibility of measuring the green sapwood mc in pine logs by combining industrial X-ray scanners and 3D-scanners. The method is shown to be suitable for identifying batches of logs in which the sapwood has begun to dry prior to sawing, rather than predicting the sapwood mc with high accuracy at the level of individual logs. In a single board, one would ideally like to measure the mc profile over the entire cross section to determine the mc gradient. However, the measured result is affected in the vicinity of the board edges. In the third publication, the existence of this problem is identified, and it is shown that it can be decreased by using correlation functions generated by finite element simulations of the measurement system. The fourth publication considers the potential to increase the measurement accuracy of the mc of single boards by combining different measurement techniques. Microwaves, X-rays and visual sorting into different wood quality classes are used. It is shown that the measurement accuracy is increased by the addition of both the Xray measurements and the visual sorting. This result is interesting because visual sorting is usually already present in the final sorting of large sawmills. This is also where the mc measurement preferably is to be performed.