Long-term monitoring of timber moisture content below the fiber saturation point using wood resistance sensors

A moisture-monitoring system has been developed that provides a network of monitoring cells, centrally monitored, to give early warning of potentially damaging failures of wood building components, generating high and persistent moisture levels, which are known to cause decay and damage. The most critical aspect of system design is the useful range of the moisture sensors and their performance and reliability, which are crucial to a low-maintenance installation and long-term customer satisfaction. The paper describes the development ofa novel moisture sensor designed to meet stringent requirements with respect to accuracy. The sensor consists of two pairs of parallel electrodes, equivalent to a network of six resistances, providing the potential for measuring moisture gradients. Electrodes are embedded within a cylindrical, high durability, wood buffer. Several measurement techniques used are evaluated. The performance of a prototype sensor used in connection with a datalogging system is described. Results demonstrate the possible benefit to the construction and timber industries in situations where there is the need for accurate long-term measurement of the moisture content, for example, in purchase, treatment, construction, and surveying.