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Sapwood Depth Tool – Proof of Principle

By Nurzhan Nursultanov and Bill Heffernan, June 2018.

Download SWP-T054 (pdf)

Executive summary

This research aims to develop a sapwood tool that can determine the sapwood/heartwood interface based on electrical resistance measurements with minimised set-up time. This report shows the first developed lab-based prototype of the sapwood tool, and describes its main operational principles, including the algorithm of sapwood depth identification. To prove the proposed concept, the sapwood tool was tested on four logs, including specimens of Pinus radiata, Pseuodtsuga menziesii, and Sequoia sempervirens. In addition, electrical conductivity of Eucalyptus globoidea is presented in this report.

The sapwood tool consists of the measuring and return probes, each of 12 mm diameter. Such a diameter provides structural strength, preventing the probes from excessive bending, and allows an operator to use a domestic battery drill, with the maximum drill bit diameter of 13 mm. Each probe has a plastic handle and socket at the top, to connect the probe to a power source. The return probe is made of brass, while the measuring probe consists of a brass tip connected to a socket by a wire, inside a plastic sleeve.

The investigated method showed promising results on selected logs, including S. sempervirens with the relatively conductive transitional zone and heartwood. The developed prototype of the sapwood tool proved the concept. However, the resolution of the tool and its current design require further improvement. Ideally, to be used under field conditions, the sapwood tool should measure electric current, with higher accuracy, during drilling and log the electric current versus depth automatically. At present, concepts for such designs are being developed. Lastly, in future work, the sapwood thickness in E. globoidea logs, and other relevant species, should be measured using the sapwood tool.

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