1、Designation: D 7438 08Standard Practice forField Calibration and Application of Hand-Held MoistureMeters1This standard is issued under the fixed designation D 7438; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. 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 practice applies to the measurement o
3、f 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 productcharac
4、teristics, 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 refere
5、ncedmeter is acceptable unless otherwise specified. Meters shallhave been calibrated by Test Methods D 4444.1.2 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
6、and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 2915 Practice for Evaluating Allowable Properties forGrades of Structural LumberD 4442 Test Methods for Direct Moisture Content Measure-ment of Wood and Wood-Base
7、 MaterialsD 4444 Test Methods for Laboratory Standardization andCalibration of Hand-Held Moisture MetersD 4933 Guide for Moisture Conditioning of Wood andWood-Based MaterialsD 6782 Test Methods for Standardization and Calibration ofIn-Line Dry Lumber Moisture Meters2.2 Other ASTM Sources:ASTM Standa
8、rds 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. Direct-current con-duct
9、ance meters are commonly referred to as “resistance”meters. Most commercial conductance meters are high-inputimpedance (about 1012V), wide-range (104to 1012V) ohmme-ters. Their scales are calibrated to read directly in moisturecontent (oven-dry mass basis) for a particular calibrationspecies and at
10、a specific reference temperature.3.1.2 dielectric metersdielectric meters transmit electro-magnetic wave energy into the wood to detect the influence ofmoisture in the wood on these waves as an estimate of moisturecontent. Wave energy is most often in the radio frequencyrange; hand-held meters commo
11、nly are placed directly on thewood 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,
12、 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, anddesig
13、n of the meter. The maximum accuracy can only beobtained by an awareness of the effect of each parameter on the1This 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 appro
14、ved April 1, 2008. Published May 2008.2For 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 Interna
15、tional, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.meter 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 add
16、resses the influence ofprocess and wood variables.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) relationshi
17、ps 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 potential need for this type of sampling. These correlativeuses are examined in
18、Appendix X3.5. Standardization5.1 GeneralStandardization shall be performed to estab-lish the integrity of the meter and electrode under the fieldconditions of use. The meter circuit shall be tested by applyingthe reference material in accordance with manufacturersrecommendations, noting the corresp
19、onding meter responsevalue, and comparing with the manufacturers data. Standard-ization shall be done before calibration. If alternate electrodesare to be used with a meter, standardization shall be done for allelectrode types and alternate assemblies.5.1.1 Initially, standardization should be perfo
20、rmed beforeeach period of use. The time interval may be extended ifexperience shows that the particular meter is stable for a longertime under equivalent use conditions.5.1.2 Standardization procedures in the field will be affectedby the standardization performance of the meter during evalu-ation un
21、der Test Methods D 4444. The report of section 5.2.3of Test Methods D 4444 provides this information.5.2 The standardization shall be carried out with the instru-ment, including electrodes, at the temperature of the antici-pated application. This shall include the range of anticipatedconditions; the
22、 reference material shall maintain its essentialcharacteristics over this range. The sensitivity of this standard-ization to temperature of the meter shall be part of theevaluation.5.2.1 If the environmental conditions change during theusage period beyond those evaluated in the initial standardiza-t
23、ion, the standardization shall be repeated.5.2.2 If the manufacturer 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 manufacturers recommendation.5.2.3 Field standardization may be
24、 difficult to carry outunder some ambient field conditions and with the electrodes tobe used. One example is the use in monitoring in-kiln perfor-mance. If the measurement conditions are difficult to reproduceor are transient (for example, in a hot dry kiln), then it shall beunderstood that the vali
25、dity of the meter readings are depen-dent upon the laboratory standardization and manufacturersrecommendations.6. Calibration6.1 GeneralUnder processing conditions, laboratory cali-bration procedures maybe impractical, particularly because ofmoisture and temperature gradients, nonstandard temperatur
26、es,unverified species within commercial species groups, nonstraight-grain wood, and common production variables such asmixtures of heartwood and sapwood. Further, these processvariables may change or invalidate some of the calibrationresults obtained under laboratory conditions in Test MethodsD 4444
27、.6.2 MethodsThe principles and procedures of calibrationin Test Methods D 4444 shall be applied to the degree possibleand relevant to develop a meaningful relationship betweenmeter readings and actual moisture content (MC).6.2.1 All field calibrations shall be referenced to direct MCmeasurements (Te
28、st Methods D 4442).6.2.2 Field calibration shall be carried out with meters thathave been laboratory standardized and calibrated for appropri-ate wood variables, such as species and temperature using TestMethods D 4444, and subsequently field standardized.6.3 Field VariablesThe calibration may be ba
29、sed onend-use environmental and product and process conditions thatare more restricted than those evaluated by Test MethodsD 4444. In addition, the process conditions may produceinteractions that must be considered in the calibration.6.3.1 Special care must be taken to minimize errors causedby the i
30、nfluence of unintended wood variables, such as densityand temperature (uncorrected) on readings. Specimen size forfield testing may be selected to represent the appropriategeometry of the target sample. Field meter readings areconditional upon both the prior standardization and calibrationprocess, t
31、he influence of wood variables in the field test, andapplication information supplied by the meter manufacturer.6.4 Calibration StepsThe field calibration shall be con-ducted on specimens and in conditions that are representativeof the process and are carefully documented. SeeAppendix X2for discussi
32、on of process variables and wood characteristics.6.4.1 Sample SelectionThe number of wood specimensused for the calibration shall be selected following the conceptsof Practice D 2915, considering the variables to be representedand the desired precision of the calibration. For example, if thesample i
33、s to represent grain patterns, moisture gradients, etc.found in a lumber grade, these variables shall be considered insetting sampling criteria. (See also Test Methods D 4444.)6.4.2 Sample PreparationWhile the sample may be in-tended to include process variables such as moisture gradients,temperatur
34、e, etc., the measurement and subsequent preserva-tion of these variables prior to and during meter measurementshall be considered part of the sampling process. See TestMethods D 4444 for discussion of other relevant issues.6.4.3 TestingField calibration shall be based on the rela-tionship of the met
35、er readings to Test Methods D 4442 mois-ture measurement values. Because process conditions may betransient (for example, temperature and moisture gradients, orboth), calibration that reflects these variables requires specialtreatment of specimens (such as subdividing specimens) oradditional equipme
36、nt (such as temperature probes). Care shallD7438082be taken to not distort the original specimen condition withthese additional steps.6.4.4 Determination of CorrectionsTo establish a correc-tion that reflects the influence of the measured variables, theprinciples of Test Methods D 4444, section 6.2.
37、4, shall befollowed.6.5 ReportUseful application of field test calibration isconditional upon the relevance of the test sample. Conse-quently, accurate reporting of the wood and process variables(see 6.3 and 6.4) is critical. The report shall follow the practiceof Test Methods D 4444, section 6.2.5.
38、6.5.1 Field samples often contain uncertainties with respectto exact species or species mixtures, temperature at the point ofelectrode measurement, in-exact moisture gradients, and otherspecimen variables. Where these non-uniformities and uncer-tainties cannot be measured or corrected, their presenc
39、e shallbe noted in the report and quantified where possible.APPENDIXES(Nonmandatory Information)X1. COMMENTARYINTRODUCTIONThe purpose of this appendix is to supply auxiliary information on the basis for and practice of thispractice. It is organized with paragraphs that correspond by section number t
40、o those in the mandatorytext; text paragraphs needing no explanation are not listed. This concept permits changes at any timein order to keep the practice current and to improve its usefulness.This is a practice standard; thus, it describes and standardizes, to the degree possible, the calibrationan
41、d measurement practices that occur outside the environment of the testing laboratory.TABLE X1.1Section Comments1.1 The principal concepts of this practice, as first incorporated in Practice D 2016 and then in subsequent editions of this practice, addressed onlymeters based on the change of wood cond
42、uctance or dielectric properties with moisture content. Specific electrode configurations wereanticipated, based on early commercial use. Conductance and dielectric meters were separated in the practice; no provisions were made otherelectrode configurations or measurement technologies. The current p
43、ractice makes no distinction between meter measurement technologies forstandardization and calibration requirements. Provision for unique characteristics of measurement technologies is accommodated in Appendix X1-Appendix X3. The use of “field” to describe calibrations and measurement issues denotes
44、 conditions that cannot be controlled as in a laboratory,yet the conditions are very commonly the environment in which the meters are used.1.1.1 This practice targets use outside of the laboratory where controlled conditions are not usually possible. In addition, most commercial woodproducts are not
45、 “clear” and straight-grain and are heterogenous in other characteristics. Sampling is necessarily tied to commercial productdescriptions.1.1.2 Requiring calibration under Test Methods D 4444 ensures prior technical evaluation of a meter, with an associated report describing performanceunder control
46、led conditions. Although the intended use may not adhere to these same conditions, the performance in the laboratory establishesthe minimum performance criteria for field use as well as reference points on sensitivity to variables such as species, density, temperature, etc.3.1 This practice is desig
47、ned to apply to meters using technologies other than the two technologies included in the section. Conductance anddielectric meters are included because they provide the generic descriptions of principal, current commercial meters. Individual characteristicsofcommercial meters are not intended to be
48、 covered in these generic descriptions. As other meter technologies are developed, more genericdescriptions should be added to this section.4.1.1 Much of the content of this practice was incorporated in previous versions and drafts of Test Methods D 4444, and some earlier in PracticeD 2016. The mixi
49、ng of test methods and practices in one standard is not desirable; thus, this practice attempts to capture the critical elements ofthe many and varied commercial applications of hand-held meters while Test Methods D 4444 concentrates on the base-line laboratory testmethods. Specific issues of meter technology in use are covered in more detail in Appendix X2.4.2 Correlative methods of data analysis are critical to many meter uses; however, they vary widely and are difficult to characterize as true calibrationof a meter. Consequently, Appendix X3 addresses both calibration
