a discoloration of their contents (Panshin and DeZeuw 1980). It is almost ubiquitous in older trees at felling age, but often affects younger specimens too. Healthy red heartwood is mostly considered a visual defect only, but, since beech is most often used in the furniture industry and interior design, red heart causes a major decrease in the perceived value, and leads to a serious drop in the retail price of beech wood (Molnar et al. 2001;Hapla and Ohnesorge 2005).There are several forms of red heart, all of which occur in beech wood. According to the characterisation by Sachsse (1991), they can be classified as red heartwood with round borders and a partly cloudy appearance on the cross-section, wounded heartwood with a small spatial extent, splashing heartwood (or dotty red heart) with jagged borders, and abnormal heartwood with black borders attacked by bacteria. In either case, the borders of red heart do not follow the annual ring boundaries. Figure 1 shows the first type, immediately after felling. In terms of its longitudinal expansion, it is most often spindle-like, but it may also be cone or upside-down cone shaped, or irregular. Red heart can also be classified as healthy or diseased, based on whether or not it has been attacked by fungi, and, as a result, they suffered some strength loss (Rumpf and Biro 2003;Wernsdörfer et al. 2005).Beech red heart has generated considerable research interest over the past decades. Wernsdörfer et al. (2005) provided a very detailed overview of the work done up to that point. Knoke (2002) provided a thorough review of the publications on heartwood formation, and concluded that reducing the amount of discolored timber is possible only based on information about the recent formation of red heartwood. He lamented the fact that non-destructive methods are not yet far enough advanced to provide information on early heartwood formation. AbstractRed heart is one of the most important visual defects in beech wood. Its detection is difficult, since its mechanical characteristics do not differ significantly from sound wood. However, its electric conductivity is different, which offers an opportunity for detecting beech red heart. Initial measurements using a 24-channel impedance tomograph were very efficient in detecting red heart due to its significantly lower electric resistance. High conductivity regions on the resistance map corresponded to the size and shape of the red heart. An 8-detector setup was investigated in a laboratory setting to establish the best electrode arrangement to develop a simple and reliable on-site detection method. On-site measurements, using only four electrodes, proved to be highly reliable to detect the presence of red heart in beech trees of 40-60 cm diameter. In the meantime, the method did not seem capable of determining the extent of red heart. The diameter of the tree was found to have very little effect on the measured voltage. Therefore, there is no need for diameter-correction in the examined diameter range.
A bükkfa egyik legjelentősebb esztétikai hibája az álgeszt, melynek elektromos tulajdonságai is eltér-nek az egészséges faanyagétól. Ez lehetőséget kínál az álgeszt elektromos ellenállás mérésen alapuló vizsgálatára. Az álgeszt kimutatására irányuló vizsgálataink során először egy 24 csatornás impedancia tomográffal vizsgáltunk bükk törzseket. A jelentősen alacsonyabb ellenállású álgesztes farész jól kirajzolódott a tomográffal előállított ellenállás-térképeken, és jó egyezést mutatott a vágásképen látható álgeszt méretével és alakjával. 8 érzékelővel végzett laboratóriumi előkísérletek segítségével megálla-pítottuk a legelőnyösebb elektróda-elrendezést, aminek a segítségével a terepen gyorsan és egyszerűen lehet vizsgálni az álgeszt jelenlétét. A tapasztalatok alapján a terepi vizsgálatokhoz kifejlesztett műszer egyértelműen alkalmasnak bizonyult az álgeszt jelenlétének a kimutatására, azonban annak kiterjedé-sét nem lehetett vele megbízhatóan megállapítani. A vizsgált átmérő tartományban a feszültség csak igen kis mértékben függ az átmérőtől, a vizsgálat az átmérőtől függetlenül megbízható, nincs szükség átmérő szerinti korrekcióra. Kulcsszavak: bükk, álgeszt, élőfa-vizsgálat, roncsolásmentes faanyagvizsgálat, impedancia tomográfia Detecting red heart in beech (Fagus sylvatica) through electric resistance and voltage measurements AbstractOne of the most important visual defects of beech is red heart, whose electric conductivity is also different from that of sound wood. This offers an opportunity for detecting red heart based on resistance measurements. First, beech trees were investigated using a 24-channel impedance tomograph. Red heart beech wood, which has a much lower electric resistance, was clearly visible on the resulting resistance maps, and it corresponded well to the size and shape seen on the trees' cross-section after felling. The laboratory investigations using 8 detectors helped establish the best arrangement of electrodes for the quick and reliable detection of red heart on site. Based on the onsite tests, the developed instrument is highly reliable for detecting the presence of red heart in beech trees of 40-60 cm in diameter, but could not consistently predict its extent. The measured voltage shows very weak correlation to diameter in the examined range; the diameter does not effect the test significantly, and there is no need for diameter-correction.
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