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Structure of timber and the presence of moisture
Published in Peter Domone, John Illston, Construction Materials, 2018
Determination of the moisture content of timber is usually carried out using the basic gravimetric technique above, though it should be noted that at least a dozen different methods have been recorded in the literature. Suffice it here to mention only two of these alternatives. First, where the timber contains volatile extractives, which would normally be lost during oven drying, thereby resulting in erroneous moisture content values, it is customary to use a distillation process, heating the timber in the presence of a water-immiscible liquid such as toluene, and collecting the condensed water vapour in a calibrated trap. Second, where ease and speed of operation are preferred to extreme accuracy, moisture content is assessed using electric moisture meters. The type most commonly used is known as the resistance meter, though this battery-powered hand-held instrument actually measures the conductance or flow (the reciprocal of resistance) of an electric current between two probes. Below the fibre saturation point (about 27% moisture content; see later) an approximately linear relationship exists between the logarithm of conductance and the logarithm of moisture content. However, this relationship, which forms the basis for this type of meter, changes with species of timber, temperature, and grain angle. Thus, a resistance-type meter is equipped with a number of alternative scales, each of which relates to a different group of timber species; it should be used at temperatures close to 20°C. with the pair of probes inserted parallel to the direction of the grain.
Structure of timber and the presence of moisture
Published in Marios Soutsos, Peter Domone, Construction Materials, 2017
Determination of moisture content in timber is usually carried out using the basic gravimetric technique above, though it should be noted that at least a dozen different methods have been recorded in the literature. Suffice it here to mention only two of these alternatives. First, where the timber contains volatile extractives, which would normally be lost during oven-drying thereby resulting in erroneous moisture content values, it is customary to use a distillation process, heating the timber in the presence of a water-immiscible liquid such as toluene, and collecting the condensed water vapour in a calibrated trap. Second, where ease and speed of operation are preferred to extreme accuracy, moisture contents are assessed using electric moisture meters. The type most commonly used is known as the resistance meter, though this battery-powered hand-held instrument actually measures the conductance or flow (the reciprocal of resistance) of an electric current between two probes. Below the fibre saturation point (about 27% moisture content, see later), an approximately linear relationship exists between the logarithm of conductance and the logarithm of moisture content. However, this relationship, which forms the basis for this type of meter, changes with species of timber, temperature and grain angle. Thus, a resistance-type meter is equipped with a number of alternative scales each of which relates to a different group of timber species; it should be used at temperatures close to 20°C with the pair of probes inserted parallel to the grain direction.
Damp: Rising damp, penetrating damp and condensation
Published in Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann, Understanding Housing Defects, 2013
Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann
Most moisture meters are specifically calibrated for timber and cannot give accurate readings (i.e. percentage moisture content) for other materials. Even with timber there are differences between timber species, and between hardwoods and softwoods. However, the differences are not particularly significant and measurements can be adjusted if an accurate moisture content is required for a known species. There are, however, one or two pitfalls which should be recognised by anyone carrying out testing to assess moisture content. For example, readings from an electric moisture meter can be affected (readings will be too high) if the timber has been treated with water-based preservatives. The temperature of the wood will also affect readings.
Real-time monitoring of milk powder moisture content during drying in a spouted bed dryer using a hybrid neural soft sensor
Published in Drying Technology, 2019
Gustavo N. A. Vieira, Martín Olazar, José T. Freire, Fábio B. Freire
In spite of the great importance of measuring the moisture content of dried products, its measurement for control purposes is not easily applicable to many different dried products. Some moisture meters are those based on some physical properties of water, such as its capacity for absorbing electromagnetic radiation in specific wavelengths, mainly at infrared and microwave frequencies.[2] Such meters are gradually being applied in chemical and food industries. However, unfortunately the online moisture content measurement techniques by electromagnetic radiation are not applicable for particulate matter (such as grains, seeds, and powders), because the voidage may cause measurement noise and diffuse reflection.[3,4] Additionally, such meters are expensive for low added value products, such as foodstuff in general.
Methods of strengthening cross-laminated timber manufactured using Irish Sitka Spruce: a preliminary study
Published in Journal of Structural Integrity and Maintenance, 2023
Emily McAllister, Daniel McPolin, Jamie Graham, Grainne O’Neill
A handheld device can be used to get instant readings of moisture content from a sample of timber. Moisture meters can either have probes to penetrate the timber or can be pinless and non-invasive to the timber using electromagnetic sensors to read the moisture content. With the testing of timber of the preliminary tests a pinned probe was used. For readings in the next tests, an Orion 910 pin-less moisture meter was used. This meter was suitable for timber with moisture between 4.0% and 32.0%. To ensure accuracy of the hand held moisture meter it was verified with the oven drying method, as outlined in Section 5.2.