A European standard "EN 13183-2 Moisture content of a piece of timber - Part 2: Determination by the electrical resistance method" describes a non-destructive method for estimating the moisture content of a piece of sawn timber using an electrical resistance moisture meter. This standard applies to sawn timber and timber that has been planed or mechanically surfaced by other means.
For the purposes of this standard, the terms and definitions in EN 844-1, EN 844-3, EN 844-4, EN 844-6, EN 844-7, EN 844-9 and EN 844-12 standards are valid.
This method is suitable for lumber with moisture content between approximately 7 percent and 30 percent. Certain types of preservative, flame retardant, heat, or chemical treatments will affect the accuracy of the measurement and require specific calibration of the instrument for each type of treatment.
These tests use an electric resistance moisture meter equipped with insulated electrodes, rated for units with a maximum moisture content of 1 percent to 30 percent. The meter should be equipped with adjustments or tables to correct for wood type and temperature.
Before measurements are taken, the electrical resistance moisture meter should be checked according to the instructions provided by the supplier of the instrument. Resistance checkboxes are available to check the accuracy of the instrument.
The following procedure is used to estimate the moisture content of individual parts in lots or shipments. The electric resistance moisture meter reading must be corrected to take into account the temperature and type of lumber being measured.
Normally the measurement is made in the direction of the grain. If specifically requested in the instrument manual, the measurement is taken at right angles to the grain. Due to the strong effects of surface moisture content and possible changes in moisture content in the cross-section, undamaged insulated electrodes should be used.
The electrodes are applied to one face of the part at a point at least 300 mm from each end of the part or at the centre point of parts shorter than 600 mm and 0,3 times the width from one edge, with the tips of the electrodes penetrating to a depth of 0,3 times the thickness of the part. The measurement area should be free of resin wood and features such as bark, knots and resin pockets. If such features are present, the measurement is made in the nearest open area towards the centre of the part. The reading is taken after viewing for 2 to 3 seconds.
When expressing results, the estimated moisture content reading is expressed at least to the nearest whole percent.
Individual test results should be recorded with at least the following information: timber lot characteristics (number, internal coding, supplier, customer, etc.), species, dimensions, date, type of tool used, species setting, temperature setting, penetration depth.
Wood is a hygroscopic material, meaning it absorbs water. Wood takes up water in three ways: as a liquid through capillary tension in the cell lumens, as vapor from the cell lumens, and as molecular diffusion through the cell walls. The moisture content of wood is the ratio of the mass of water in the wood to the mass of the timber that does not contain water. In other words, the moisture content of wood is calculated by dividing the moisture content by the amount of dry material in kg. The moisture content is defined as the ratio of the weight of the wet material to the weight of the dried wood after drying at 103 degrees. For example, if a 100-kg piece of wood contains 50 kg of water, the moisture content is 100 percent. The moisture content of freshly cut wood is usually between 40 percent and 200 percent. In normal use, the moisture content of wood varies between 8 percent and 25 percent by weight, depending on the relative humidity of the air.
Moisture and water affect the properties of wood during both processing and use. For example, moisture content affects key properties such as dimensions, durability, and resistance to deterioration, as well as planing, gluing, and surface treatment. As a result, understanding how moisture affects wood and how to test for moisture content is critical.
Among the numerous tests, measurements, analyses and evaluations that our organization has carried out for businesses in various sectors, it also provides testing services defined in the standard “EN 13183-2 Moisture content of a piece of timber - Part 2: Determination by electrical resistance method” with its trained and expert staff and advanced technological equipment.
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