Active Standard ASTM D7438 | Developed by Subcommittee: D07.01
Book of Standards Volume: 04.10
Historical (view previous versions of standard)
Significance and Use
4.1 Hand-held meters provide a rapid means of sampling moisture content of wood-based materials during and after processing to maintain quality assurance and compliance with standards. However, these measurements are inferential; that is, electrical parameters are measured and compared against a calibration to obtain an indirect measure of moisture content. The electrical measurements are influenced by actual moisture content, a number of other wood variables, environmental conditions, geometry of the measuring probe circuitry, and design of the meter. The maximum accuracy can only be obtained by an awareness of the effect of each parameter on the meter output and correction of readings as specified by these test methods. Appendix X1 is a commentary that provides explanation of the mandatory sections and discussion of historical practices. Appendix X2 addresses the influence of process and wood variables.
4.2 Most uses of hand-held moisture meters employ correlative (predictive) relationships between the meter reading and wood areas or volumes that exceed that of the direct meter measurement (for example, larger specimens, pieces of lumber, lots). The field calibration section of this practice anticipates the potential need for this type of sampling. These correlative uses are examined in Appendix X3.
1.1 This practice applies to the measurement of moisture content of solid wood, including solid wood products containing additives, that is, chemicals or adhesives, by hand-held moisture meters under conditions of end-use.
1.1.1 This practice includes calibration, use, and interpretation of meters for conditions that relate to wood product characteristics, such as nonuniform grain and growth ring orientation, and to end-use process conditions, such as moisture gradients.
1.1.2 Meters employing differing technologies may not provide equivalent readings under the same conditions. When this practice has been applied, it is assumed that the referenced meter is acceptable unless otherwise specified. Meters shall have been calibrated by Test Methods D4444.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D2915 Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
D4442 Test Methods for Direct Moisture Content Measurement of Wood and Wood-Base Materials
D4444 Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters
D4933 Guide for Moisture Conditioning of Wood and Wood-Based Materials
D6782 Test Methods for Standardization and Calibration of In-Line Dry Lumber Moisture Meters
Other ASTM Sources
ICS Number Code 79.120.99 (Other woodworking equipment)