ASTM_D_7438_-_13.pdf

Designation:D743813Standard Practice forField Calibration and Application of Hand-Held MoistureMeters1This standard is issued under the fixed designation D7438;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice applies to the measurement of moisturecontent of solid wood,including solid wood products contain-ing additives,that is,chemicals or adhesives,by hand-heldmoisture meters under conditions of end-use.1.1.1 This practice includes calibration,use,and interpreta-tion of meters for conditions that relate to wood productcharacteristics,such as nonuniform grain and growth ringorientation,and to end-use process conditions,such as mois-ture gradients.1.1.2 Meters employing differing technologies may notprovide equivalent readings under the same conditions.Whenthis practice has been applied,it is assumed that the referencedmeter is acceptable unless otherwise specified.Meters shallhave been calibrated by Test Methods D4444.1.2 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D2915 Practice for Sampling and Data-Analysis for Struc-tural Wood and Wood-Based ProductsD4442 Test Methods for Direct Moisture Content Measure-ment of Wood and Wood-Base MaterialsD4444 Test Method for Laboratory Standardization andCalibration of Hand-Held Moisture MetersD4933 Guide for Moisture Conditioning of Wood andWood-Based MaterialsD6782 Test Methods for Standardization and Calibration ofIn-Line Dry Lumber Moisture Meters2.2 Other ASTM Sources:ASTM Standards on Precision and Bias for VariousApplications,19923.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 conductance metersconductance meters are thosethat measure predominantly ionic conductance between pointsof applied voltage,usually direct current.Direct-current con-ductance meters have been commonly referred to as“resistance-type”meters.Most commercial conductance me-ters are high-input impedance(about 1012),wide-range(104to 1012)ohmmeters.Their scales are calibrated to readdirectly in moisture content(oven-dry mass basis)for aparticular calibration species and at a specific reference tem-perature.3.1.2 capacitive-admittance meterscapacitive-admittancemeters transmit electromagnetic wave energy into the wood todetect the influence of moisture in the wood on these waves asan estimate of moisture content.Wave energy is most often inthe radio frequency range;hand-held meters commonly areplaced directly on the wood surface.4.Significance and Use4.1 Hand-held meters provide a rapid means of samplingmoisture content of wood-based materials during and afterprocessing to maintain quality assurance and compliance withstandards.However,these measurements are inferential;thatis,electrical parameters are measured and compared against acalibration to obtain an indirect measure of moisture content.The electrical measurements are influenced by actual moisturecontent,a number of other wood variables,environmentalconditions,geometry of the measuring probe circuitry,anddesign of the meter.The maximum accuracy can only beobtained by an awareness of the effect of each parameter on themeter output and correction of readings as specified by thesetest methods.Appendix X1 is a commentary that providesexplanation of the mandatory sections and discussion ofhistorical practices.Appendix X2 addresses the influence ofprocess and wood variables.1This practice is under the jurisdiction of ASTM Committee D07 on Wood andis the direct responsibility of Subcommittee D07.01 on Fundamental Test Methodsand Properties.Current edition approved April 1,2013.Published May 2013.Originallyapproved in 2008.Last previous edition approved in 2008 as D743808.DOI:10.1520/D7438-13.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.1.1 This practice provides for calibration and applicationof wood products that contain commercial characteristics andthat reflect the manufacturing environment.4.2 Most uses of hand-held moisture meters employ correla-tive(predictive)relationships between the meter reading andwood areas or volumes that exceed that of the direct metermeasurement(for example,larger specimens,pieces of lumber,lots).The field calibration section of this practice anticipatesthe potent