In heritage collections and various structures, stresses in wood can occur due to temperature, moisture and relative humidity. Development of strain due to these stresses can lead to damage, fracture, permanent deformation. Therefore, it is important that the strain in the wood caused by environmental variations is continuously monitored. For these varying environmental conditions, the wooden objects must continuously adapt themselves. There are some monitoring methods that help in determining whether the dimensional changes of wood are acceptable. Strain gauges are one of the monitoring methods that can be used in this scenario.
For a heterogeneous material like wood, a gauge length of 4 to 5 times the heterogeneities is required. Therefore, the PFLW/PLW series strain gauge from TML, especially designed for measurements in wood, is utilised for this application. The strain gauge facilitates long-term measurement on wood by converting the mechanical strain caused by changing hygro-thermal conditions into a change in the electrical resistance. These gauges have a metal foil lined on the back for protection against the influence of moisture in the wood. These strain gauges feature an especially designed grid that reduces the stiffening effect of the strain gauges to the specimen wood. The strain gauges are available with 1, 3 or 5m long in 2-wire parallel or 3-wire parallel vinyl lead wires.