1、Designation: D 4444 08Standard Test Method forLaboratory Standardization and Calibration of Hand-HeldMoisture Meters1This standard is issued under the fixed designation D 4444; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method applies to th
3、e measurement of moisturecontent (MC) of solid wood products, including those contain-ing additives (that is, chemicals or adhesives) for laboratorystandardization and calibration of hand-held moisture meters1.2 This test method makes no distinction between metermeasurement technologies for standard
4、ization and calibrationrequirements. Provision is made for test specimen size toaccommodate specific meters. Appendix X1 provides an ex-planatory discussion and history corresponding to the manda-tory sections. Fundamental measurement technologies aredescribed in Appendix X2 when available.1.2.1 Met
5、ers employing differing technologies may notprovide equivalent readings under the same conditions. Whenthis test method has been applied, it is assumed that thereferenced meter is acceptable unless otherwise specified.Meters shall be calibrated with respect to MC by directmeasurement as determined b
6、y Test Methods D 4442.1.3 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
7、to use.2. Referenced Documents2.1 ASTM Standards:2D 1990 Practice for Establishing Allowable Properties forVisually-Graded Dimension Lumber from In-Grade Testsof Full-Size SpecimensD 2915 Practice for Evaluating Allowable Properties forGrades of Structural LumberD 4442 Test Methods for Direct Moistu
8、re Content Measure-ment of Wood and Wood-Base MaterialsD 4933 Guide for Moisture Conditioning of Wood andWood-Based MaterialsD 5536 Practice for Sampling Forest Trees for Determina-tion of Clear Wood PropertiesD 7438 Practice for Field Calibration and Application ofHand-Held Moisture Meters2.2 Other
9、 ASTM Sources:ASTM Standards on Precision and Bias for Various Appli-cations, 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
10、. Direct-current con-ductance meters are commonly referred to as “resistance”meters. Most commercial conductance meters are high-inputimpedance (about 1012V), wide-range (104to 1012V) ohm-meters.3.1.2 dielectric metersDielectric meters transmit electro-magnetic wave energy into the wood to detect th
11、e influence ofmoisture in the wood on these waves as an estimate of MC.Wave energy is most often in the radiofrequency range;hand-held meters commonly are placed directly on the woodsurface.4. Significance and Use4.1 Hand-held meters provide a rapid means of samplingMC of wood-based materials during
12、 and after processing tomaintain quality assurance and compliance with standards.These measurements are influenced by actual MC, a number ofother wood variables, environmental conditions, geometry ofthe measuring probe circuitry, and design of the meter. Themaximum accuracy can only be obtained by a
13、n awareness of1This test method is under the jurisdiction of ASTM Committee D07 on Woodand is the direct responsibility of Subcommittee D07.01 on Fundamental TestMethods and Properties.Current edition approved April 1, 2008. Published May 2008. Originallyapproved in 1984. Last previous edition appro
14、ved in 2003 as D 4444 92 (2003).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.1Copyright ASTM International
15、, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the effect of each parameter on the meter output and correctionof readings as specified by this test method.4.1.1 This test method employs controlled conditions andstraight-grain, clear wood specimens to provide me
16、asurementsthat are reproducible in a laboratory. The controlled conditionsprevent moisture and temperature gradients in the test speci-men.4.1.2 In laboratory calibration, the reference direct moisturemeasurements (for example, Test Methods D 4442) shall bemade only in the area of direct measurement
17、 of the meter. Thisminimizes error associated with sampling of differing areas ofmeasurement between this test method and that of the reference(Test Methods D 4442).4.2 Most uses of hand-held moisture meters employ correla-tive (predictive) relationships between the meter reading andwood areas or vo
18、lumes that exceed that of the direct metermeasurement (for example, larger specimens, pieces of lumber,or lots). These correlative relationships are beyond the scope ofthis test method. (See Practice D 7438.)5. Standardization5.1 GeneralStandardization provides a measured relation-ship to a standard
19、 reference material that can be used to ensurethat a meter is operating properly. Standardization shall beperformed to establish the integrity of the meter and electrode.Standardization shall be done before calibration and use. Ifalternate electrodes can be used with a meter, standardizationshall be
20、 done for all electrode types and alternate assemblies.5.2 Standardization shall be based, where feasible, on thedirect measurement region of the meter as supplied by themeter manufacturer. If not supplied by the manufacturer, thearea of direct measurement shall be determined by test.5.2.1 If the ma
21、nufacturer recommends an area, a method, ora standard specimen for standardization that does not reflect theentire direct measurement area of the meter, this shall be notedas the manufacturer recommendation.5.2.2 The meter circuit and electrode shall be tested withexternal reference material to veri
22、fy the precision and bias inthe meter response range of anticipated use. The meter shall beevaluated over the range of environmental conditions recom-mended by the manufacturer. The sensitivity of this standard-ization procedure to temperature of the meter shall be part ofthe evaluation.5.2.2.1 The
23、sensitivity of the standardization reference ma-terial to the range of environmental conditions in 5.2.2 shall beevaluated.5.2.3 ReportThe report shall indicate (in the metermanual, on the meter or meter scale, or on the suppliedreference standard) the meter model, and the electrodes forwhich the st
24、andardization is valid. The sensitivity of the meter,the electrode assembly and the reference material, as evaluatedin 5.2.2.1, shall be reported.5.2.3.1 The manufacturers recommendation on frequencyof standardization shall be included in the report.6. Calibration6.1 GeneralCalibration of a meter an
25、d the electrode shallestablish reference data to adjust meter response for species,ambient conditions, and specimen variables, such as size anddensity. Meter and electrode assemblies shall be standardizedin accordance with Section 5 prior to calibration.6.2 Calibration:6.2.1 Area of MeasurementCalib
26、ration shall be based,where feasible, on the direct measurement region of the meteras supplied by the meter manufacturer. If not supplied by themanufacturer, the area of direct measurement shall be deter-mined by test. Every effort shall be made to quantify thecapability of the meter assembly to est
27、imate moisture contentby reducing extraneous sources of error.6.2.2 Sampling and AnalysisThis calibration procedure isdesigned for full-scale calibration of the meter and electrodeassembly. If only a limited portion of the scale requirescalibration, the number of equilibrium moisture content (EMC)le
28、vels can be reduced to as low as two. Calibration should notbe extrapolated below the lowest value. Extrapolation above21 % EMC to the fiber saturation point is permissible, providedthat caution be taken in regression extension beyond themoisture data high end point. Calculation of confidence limite
29、nvelopes are recommended with use of regression in thisfashion. Stratified sampling and analysis of variance, or both,can be applied to quantify sensitivity to wood characteristics. Ifthe test material is other than solid wood, it shall be preparedand tested in a manner consistent with the solid woo
30、d calibra-tion procedures.6.2.2.1 Wood CharacteristicsWood characteristics thatneed to be treated as measurement variables because they mayinfluence meter readings shall be represented in the calibrationsampling. Examples of these variables are density and mineralcontent. These characteristics shall
31、 be included, identified, andmeasured as part of random sampling from a target populationor they shall be sampled separately as part of a strategy ofstratified sampling.6.2.3 Sample PreparationThe sample size shall be basedon the sampling principles of Practice D 2915, Section 3.4,based upon subsequ
32、ent subdivision of the sample into sub-setsfor conditioning and testing. Specimen size shall be selected toencompass the direct measurement region of the meter/electrode assembly with minimal excess material. Specimensmust be free of visible irregularities such as knots, decay,reaction wood, and res
33、in concentrations. The specimens shallbe conditioned at 25 6 1C and selected relative humidities toeach of five EMC levels between 7 and 21 % (see GuideD 4933).Alternatively, specimens may be equilibrated (follow-ing a desorption path) at each of the five EMC conditions.6.2.3.1 SpeciesSpecies shall
34、be identified. If the samplerepresents a species group, the individual species of eachspecimen shall be identified if anatomically possible.6.2.3.2 Sapwood/HeartwoodSpecimens shall be chosen tobe entirely sapwood or heartwood, or two separate groups ofeach, but not mixed in the same specimens. It sh
35、all be reportedif sapwood/heartwood mixing is unavoidable.6.2.3.3 Wood CharacteristicsSpecimen selection forwood characteristics shall be considered in setting sample size.6.2.4 TestingThere are two steps in the testing phase ofcalibration. The first is meter measurements on the woodsamples followin
36、g the procedures of this test method and theapplicable criteria provided by the manufacturer. The secondD4444082step is conducting a direct moisture content determinationfollowing Test Methods D 4442.6.2.4.1 Meter MeasurementThe equilibrated specimensare numbered, weighed, and a meter measurement ta
37、ken withthe electrode aligned on the specimen in accordance with themanufacturers recommendation. The speed of response of themeter will determine the timing of the meter reading; manu-facturers recommendations shall be followed unless thisvariable is examined as part of the calibration process.6.2.
38、4.2 Direct Moisture TestThe MC of each specimenshall be determined by the appropriate direct method (TestMethods D 4442) after the meter measurement. Proceduresshall be followed to prevent moisture gain or loss from thespecimens between the meter measurement and the direct test.6.2.5 Correction Fact
39、or DeterminationThe correctionsapplied to moisture meters and the precision and bias of themeters may differ significantly between the technology em-ployed and manufacturing variables. Wood characteristics,species, temperature and chemical additives are specimenvariables that may require correction
40、factors. The followingprocedures shall be followed to determine correction factorsfor meters.6.2.5.1 Correction for Wood Sample CharacteristicsThemoisture meter scale readings determined from 6.2.4.1 proce-dures shall be related to the corresponding MC from 6.2.4.2 foreach specimen in the sample by
41、regression or analysis ofvariance analysis.(1) Species calibrations that are intended to represent anentire species (for example, to correspond to globally-determined design values assigned to structural products) shallbe obtained only by conducting species-wide sampling.(2) The species sampling sug
42、gested in this test method isnot required to be species-wide. Species representation claimsbased on less-than species-wide sampling shall be correspond-ingly limited.6.2.5.2 Correction for Wood Sample TemperatureThiscorrection shall be applied after the meter has been standard-ized in accordance wit
43、h Section 5 and calibrated in accordancewith 6.2.5.1. The options for this correction are to use astandard temperature correction or to conduct a laboratorycalibration.(1) Determination of Temperature CorrectionThe correc-tion shall be based on samples prepared as specified in 6.2.2except that speci
44、mens of known MC (Guide D 4933)at25 6 1C (77 6 1.8F) shall be placed, with electrodes andtemperature probes attached, in a sealed container. The changein indicated MC (meter indication) shall be recorded whilechanging temperature through the desired range. A final meterreading must be made at 25 6 1
45、C (77 6 1.8F) to confirmthat the MC has not varied from the temperature cycling.(2) Standard Temperature CorrectionIf a laboratory de-termination is not made for conductance meters, the followingrelationship shall be used to correct MC below the fibersaturation point over the temperature range of 0
46、to 40C.MC25 MC11 0.06MC10.5!T22 25! (1)where:MC1= the MC at 25C.This information is presented in Appendix X2.6.2.5.3 Correction for Chemical AdditivesMeter assem-blies applied to wood materials that have been treated withadditives and have adhesives interspersed with the fiber, orboth, shall be cali
47、brated with those materials following theprecepts of this and previous sections on sampling and prepa-ration. Some discretion is appropriate on temperature andmoisture levels, depending on the end use of the products.6.2.6 ReportThe following wood sample informationshall be recorded: MC, size (dimen
48、sions in each plane), speciesand method of species identification, sapwood/heartwood per-centage, density or specific gravity, growth rate (rings/25 mm)and ring orientation, and earlywood/latewood percentage. Forother materials, the appropriate wood sample information shallbe recorded together with
49、adequate data to identify the productand its constituents. The following meter information shall berecorded: manufacturer and model, reference temperature, andelectrode type and configuration. The following standardiza-tion and calibration information shall be reported: method ofanalyses and presentation, influence of wood characteristics(variables), influence of temperature and method of correction,and details of electrode placement.6.2.6.1 If a meter is not accompanied by the calibration dataof 6.2.5 or by a discussion of sensitivity of the meter too
