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Small resistive wood moisture sensors: a method for moisture content determination in wood structures

Kleine widerstandsbasierte Sensoren zur Bestimmung der Holzfeuchte in Holzkonstruktionen

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Abstract

The wood moisture content influences the service life of wood structures since wood is susceptible to decay by rot fungi if it is exposed to high moisture contents during long periods of time. In rain exposed structures, the moisture content close to end grain surfaces and joints can be significantly higher than the average moisture content, but moisture content determinations at such locations require small moisture content sensors. This paper presents small resistive moisture content sensors fastened by electrically conductive adhesive. The relationship between moisture content and electrical resistance was determined for Norway spruce (Picea abies (L.) Karst.) for a wide range of moisture conditions achieved both by equilibrating specimens over saturated salt solutions and by the pressure plate method. The error, i.e. the difference between the gravimetric moisture content and the moisture content from the regression equation, increased with increasing moisture content. Neither the wood type (heartwood/sapwood) nor the growth rate (southern or northern Sweden) influenced the resistance-moisture content relationship.

Zusammenfassung

Die Holzfeuchte hat einen Einfluss auf die Nutzungsdauer von Holzkonstruktionen, da Holz anfällig für Pilzbefall ist, wenn es über einen längeren Zeitraum hoher Feuchte ausgesetzt ist. Bei Konstruktionen, die Regen ausgesetzt sind, kann der Feuchtegehalt im Hirnholzbereich und im Bereich von Verbindungen deutlich höher als der mittlere Feuchtegehalt sein. Zur Bestimmung des Feuchtegehalts an diesen Stellen sind kleine Feuchtesensoren erforderlich. In diesem Artikel werden kleine widerstandsbasierte Feuchtesensoren vorgestellt, die mit elektrisch leitfähigem Klebstoff befestigt werden. Der Zusammenhang zwischen Feuchtegehalt und elektrischem Widerstand wurde am Fichtenholz (Picea abies (L.) Karst.) in einem weiten Feuchtebereich bestimmt, wobei die Feuchten sowohl durch Lagerung über gesättigten Salzlösungen als auch mittels der Drucktopfmethode eingestellt wurden. Der Fehler, d.h. die Differenz zwischen dem gravimetrischem und dem über die Regressionsgleichung ermittelten Feuchtegehalt nahm mit steigendem Feuchtegehalt zu. Weder die Art des Holzes (Kernholz/Splintholz) noch die Wuchsbedingungen (Süd- oder Nordschweden) hatten einen Einfluss auf die Beziehung zwischen Widerstand und Holzfeuchte.

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Acknowledgments

Thomas Ulvcrona, Swedish University of Agricultural Sciences, is gratefully acknowledged for providing the wood material used in this study. Thord Lundgren, Division of Structural Mechanics, Lund University is gratefully acknowledged for building the logger. This work is part of WoodBuild, a research programme within the Sectoral R&D Programme 2006–2012 for the Swedish forest-based industry. This Programme is jointly funded by the government, industry and other stakeholders with interests related to the Swedish forest-based industry.

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  1. Division of Building Materials, Lund University, Box 118, 221 00, Lund, Sweden

    Maria Fredriksson, Lars Wadsö & Peter Johansson

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  1. Maria Fredriksson
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  2. Lars Wadsö
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  3. Peter Johansson
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Correspondence to Maria Fredriksson.

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Fredriksson, M., Wadsö, L. & Johansson, P. Small resistive wood moisture sensors: a method for moisture content determination in wood structures. Eur. J. Wood Prod. 71, 515–524 (2013). https://doi.org/10.1007/s00107-013-0709-0

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