ASTM D4444-13(2018)

Standard Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters

SIGNIFICANCE AND USE
4.1 Hand-held meters provide a rapid means of sampling MC of wood-based materials during and after processing to maintain quality assurance and compliance with standards. These measurements are influenced by actual MC, 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 this test method.  
4.1.1 This test method employs controlled conditions and straight-grain, clear wood specimens to provide measurements that are reproducible in a laboratory. The controlled conditions prevent moisture and temperature gradients in the test specimen.  
4.1.2 In laboratory calibration, the reference direct moisture measurements (for example, Test Methods D4442) shall be made only in the area of direct measurement of the meter. This minimizes error associated with sampling of differing areas of measurement between this test method and that of the reference (Test Methods D4442).  
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, or lots). These correlative relationships are beyond the scope of this test method. (See Practice D7438.)
SCOPE
1.1 This test method applies to the measurement of moisture content (MC) of solid wood products, including those containing additives (that is, chemicals or adhesives) for laboratory standardization and calibration of hand-held moisture meters  
1.2 This test method makes no distinction between meter measurement technologies for standardization and calibration requirements. Provision is made for test specimen size to accommodate specific meters. Appendix X1 provides an explanatory discussion and history corresponding to the mandatory sections. Fundamental measurement technologies are described in Appendix X2 when available.  
1.2.1 Meters employing differing technologies may not provide equivalent readings under the same conditions. When this test method has been applied, it is assumed that the referenced meter is acceptable unless otherwise specified. Meters shall be calibrated with respect to MC by direct measurement as determined by Test Methods D4442.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Jun-2018
• ICS: 79.080 - Semi-manufactures of timber
• ICS: 79.120.99 - Other woodworking equipment
• Technical Committee: D07 - Wood
• Drafting Committee: D07.01 - Fundamental Test Methods and Properties

Relations

• Replaces: ASTM D4444-13 - Standard Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters
• Effective Date: 01-Jul-2018
• Refers: ASTM D4442-20 - Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• Effective Date: 01-Mar-2020
• Refers: ASTM D4442-16 - Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• Effective Date: 15-Nov-2016
• Refers: ASTM D1990-16 - Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens
• Effective Date: 01-May-2016
• Refers: ASTM D5536-15 - Standard Practice for Sampling Forest Trees for Determination of Clear Wood Properties
• Effective Date: 01-Nov-2015
• Refers: ASTM D4442-15 - Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• Effective Date: 01-Jun-2015
• Refers: ASTM D1990-14 - Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens
• Effective Date: 15-Feb-2014
• Refers: ASTM D2915-10 - Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
• Effective Date: 01-Nov-2010
• Refers: ASTM D4933-99(2010) - Standard Guide for Moisture Conditioning of Wood and Wood-Base Materials
• Effective Date: 01-May-2010
• Refers: ASTM D5536-94(2010) - Standard Practice for Sampling Forest Trees for Determination of Clear Wood Properties
• Effective Date: 01-May-2010
• Refers: ASTM D7438-08 - Standard Practice for Field Calibration and Application of Hand-Held Moisture Meters
• Effective Date: 01-Apr-2008
• Refers: ASTM D1990-07 - Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens
• Effective Date: 01-Dec-2007
• Refers: ASTM D4442-07 - Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Base Materials
• Effective Date: 15-Nov-2007
• Refers: ASTM D2915-03 - Standard Practice for Evaluating Allowable Properties for Grades of Structural Lumber
• Effective Date: 10-Apr-2003
• Refers: ASTM D2915-02 - Standard Practice for Evaluating Allowable Properties for Grades of Structural Lumber
• Effective Date: 10-Nov-2002

Overview

ASTM D4444-13(2018), Standard Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters, is an internationally recognized test method developed by ASTM International. This standard outlines procedures for the laboratory standardization and calibration of hand-held moisture meters used to measure moisture content (MC) in solid wood products, including products with additives such as adhesives or chemicals.

Hand-held moisture meters offer a quick and effective way to assess moisture content during and after wood processing, making them essential tools for quality control and compliance with regulatory standards in the wood industry.

Key Topics

• Controlled Laboratory Conditions: The standard prescribes using straight-grain, clear wood specimens under controlled temperature and humidity to ensure accurate and reproducible results. This minimizes external variables such as moisture and temperature gradients that can skew measurements.
• Applicability: The method applies to all recognized hand-held moisture meter technologies, including conductance (resistance-type) and capacitive-admittance meters, without distinction.
• Calibration Reference: Calibration is performed using direct moisture content measurement methods, typically ASTM D4442, ensuring that meter readings can be reliably correlated to actual wood moisture.
• Standardization Procedure: Detailed steps are provided to ensure the meter and electrode assemblies are functioning correctly before calibration. Standardization is essential for achieving consistency in meter response and reducing measurement error.
• Influence of Variables: The method stresses the importance of considering wood variables (such as species, density, sapwood/heartwood ratio), environmental conditions (temperature, humidity), and meter characteristics (probe geometry, technology type) when conducting calibration.
• Correction Factors: The standard emphasizes deriving correction factors to account for sample temperature, wood characteristics, and chemical treatments. Proper application of these factors improves the meter's accuracy and reliability.
• Reporting Requirements: Documentation must include details about the meter, electrode configuration, sample properties, calibration procedures, and any correction factors used, supporting transparency and repeatability.

Applications

The practical value of ASTM D4444-13(2018) lies in its use for:

• Quality Assurance in Wood Products: Ensures hand-held moisture meters are properly calibrated, enabling reliable on-site measurements for quality control in lumber, engineered wood, and other wood-based products.
• Compliance with Industry Standards: Satisfies the requirements for moisture measurement in production and post-production processes, supporting compliance with national and international regulations.
• Calibration of New or Existing Moisture Meters: Provides a systematic approach to calibrate new devices or verify calibration of existing hand-held moisture meters under laboratory conditions.
• Supporting Material Research: Facilitates accurate measurement of wood moisture for laboratory studies, essential for product development and material science.
• Consistency in Global Trade: By following internationally recognized principles established by the World Trade Organization Technical Barriers to Trade (TBT) Committee, the standard enhances confidence in test results across international markets.

Related Standards

For enhanced measurement accuracy, users of ASTM D4444-13(2018) should also consider the following related ASTM standards:

• ASTM D4442: Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• ASTM D7438: Practice for Field Calibration and Application of Hand-Held Moisture Meters
• ASTM D1990: Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens
• ASTM D2915: Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
• ASTM D4933: Guide for Moisture Conditioning of Wood and Wood-Based Materials
• ASTM D5536: Practice for Sampling Forest Trees for Determination of Clear Wood Properties

These standards complement ASTM D4444 by addressing direct reference measurements, field calibration procedures, and best practices for sampling and conditioning wood specimens.

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By adhering to ASTM D4444-13(2018), stakeholders in the wood products industry can ensure accurate, traceable, and reproducible calibration of hand-held moisture meters, supporting product integrity, regulatory compliance, and customer confidence.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D4444 − 13 (Reapproved 2018)
Standard Test Method for
Laboratory Standardization and Calibration of Hand-Held
Moisture Meters
This standard is issued under the fixed designation D4444; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 2. Referenced Documents
1.1 Thistestmethodappliestothemeasurementofmoisture 2.1 ASTM Standards:
content (MC) of solid wood products, including those contain- D1990 Practice for Establishing Allowable Properties for
ing additives (that is, chemicals or adhesives) for laboratory Visually-Graded Dimension Lumber from In-Grade Tests
standardization and calibration of hand-held moisture meters of Full-Size Specimens
D2915 Practice for Sampling and Data-Analysis for Struc-
1.2 This test method makes no distinction between meter
tural Wood and Wood-Based Products
measurement technologies for standardization and calibration
D4442 Test Methods for Direct Moisture Content Measure-
requirements. Provision is made for test specimen size to
ment of Wood and Wood-Based Materials
accommodate specific meters. Appendix X1 provides an ex-
D4933 Guide for Moisture Conditioning of Wood and
planatory discussion and history corresponding to the manda-
Wood-Based Materials
tory sections. Fundamental measurement technologies are
D5536 Practice for Sampling ForestTrees for Determination
described in Appendix X2 when available.
of Clear Wood Properties
1.2.1 Meters employing differing technologies may not
D7438 Practice for Field Calibration and Application of
provide equivalent readings under the same conditions. When
Hand-Held Moisture Meters
this test method has been applied, it is assumed that the
2.2 Other ASTM Sources:
referenced meter is acceptable unless otherwise specified.
ASTM Standards on Precision and Bias for Various
Meters shall be calibrated with respect to MC by direct
Applications, 1992
measurement as determined by Test Methods D4442.
1.3 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions of Terms Specific to This Standard:
responsibility of the user of this standard to establish appro-
3.1.1 conductance meters—Conductance meters are those
priate safety, health, and environmental practices and deter-
that measure predominantly ionic conductance between points
mine the applicability of regulatory limitations prior to use.
of applied voltage, usually direct current. Direct-current con-
1.4 This international standard was developed in accor-
ductance meters are commonly referred to as “resistance”
dance with internationally recognized principles on standard-
meters. Most commercial conductance meters are high-input
ization established in the Decision on Principles for the
12 4 12
impedance (about 10 Ω), wide-range (10 to 10 Ω) ohm-
Development of International Standards, Guides and Recom-
meters.
mendations issued by the World Trade Organization Technical
3.1.2 capacitive-admittance meters—Capacitive-admittance
Barriers to Trade (TBT) Committee.
meters transmit electromagnetic wave energy into the wood to
detect the influence of moisture in the wood on these waves as
This test method is under the jurisdiction of ASTM Committee D07 on Wood
and is the direct responsibility of Subcommittee D07.01 on Fundamental Test
Methods and Properties. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2018. Published August 2018. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1984. Last previous edition approved in 2013 as D4444–13. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D4444-13R18. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4444 − 13 (2018)
an estimate of MC. Wave energy is most often in the radiof- 5.2.3 Report—The report shall indicate (in the meter
requency range; hand-held meters commonly are placed di- manual, on the meter or meter scale, or on the supplied
rectly on the wood surface. reference standard) the meter model, and the electrodes for
which the standardization is valid. The sensitivity of the meter,
4. Significance and Use
the electrode assembly and the reference material, as evaluated
in 5.2.2.1, shall be reported.
4.1 Hand-held meters provide a rapid means of sampling
5.2.3.1 The manufacturer’s recommendation on frequency
MC of wood-based materials during and after processing to
maintain quality assurance and compliance with standards. of standardization shall be included in the report.
These measurements are influenced by actual MC, a number of
other wood variables, environmental conditions, geometry of 6. Calibration
the measuring probe circuitry, and design of the meter. The
6.1 General—Calibration of a meter and the electrode shall
maximum accuracy can only be obtained by an awareness of
establish reference data to adjust meter response for species,
the effect of each parameter on the meter output and correction
ambient conditions, and specimen variables, such as size and
of readings as specified by this test method.
density. Meter and electrode assemblies shall be standardized
4.1.1 This test method employs controlled conditions and
in accordance with Section 5 prior to calibration.
straight-grain, clear wood specimens to provide measurements
6.2 Calibration:
that are reproducible in a laboratory. The controlled conditions
6.2.1 Area of Measurement—Calibration shall be based,
prevent moisture and temperature gradients in the test speci-
where feasible, on the direct measurement region of the meter
men.
as supplied by the meter manufacturer. If not supplied by the
4.1.2 In laboratory calibration, the reference direct moisture
manufacturer, the area of direct measurement shall be deter-
measurements (for example, Test Methods D4442) shall be
mined by test. Every effort shall be made to quantify the
made only in the area of direct measurement of the meter. This
capability of the meter assembly to estimate moisture content
minimizes error associated with sampling of differing areas of
by reducing extraneous sources of error.
measurementbetweenthistestmethodandthatofthereference
6.2.2 Sampling and Analysis—This calibration procedure is
(Test Methods D4442).
designed for full-scale calibration of the meter and electrode
4.2 Mostusesofhand-heldmoisturemetersemploycorrela-
assembly. If only a limited portion of the scale requires
tive (predictive) relationships between the meter reading and
calibration,thenumberofequilibriummoisturecontent(EMC)
wood areas or volumes that exceed that of the direct meter
levels can be reduced to as low as two. Calibration should not
measurement(forexample,largerspecimens,piecesoflumber,
be extrapolated below the lowest value. Extrapolation above
orlots).Thesecorrelativerelationshipsarebeyondthescopeof
21 %EMCtothefibersaturationpointispermissible,provided
this test method. (See Practice D7438.)
that caution be taken in regression extension beyond the
moisture data high end point. Calculation of confidence limit
5. Standardization
envelopes are recommended with use of regression in this
5.1 General—Standardizationprovidesameasuredrelation-
fashion. Stratified sampling and analysis of variance, or both,
ship to a standard reference material that can be used to ensure
canbeappliedtoquantifysensitivitytowoodcharacteristics.If
that a meter is operating properly. Standardization shall be
the test material is other than solid wood, it shall be prepared
performed to establish the integrity of the meter and electrode.
and tested in a manner consistent with the solid wood calibra-
Standardization shall be done before calibration and use. If
tion procedures.
alternate electrodes can be used with a meter, standardization
6.2.2.1 Wood Characteristics—Wood characteristics that
shall be done for all electrode types and alternate assemblies.
need to be treated as measurement variables because they may
5.2 Standardization shall be based, where feasible, on the influence meter readings shall be represented in the calibration
direct measurement region of the meter as supplied by the sampling. Examples of these variables are density and mineral
meter manufacturer. If not supplied by the manufacturer, the content. These characteristics shall be included, identified, and
area of direct measurement shall be determined by test. measured as part of random sampling from a target population
5.2.1 If the manufacturer recommends an area, a method, or or they shall be sampled separately as part of a strategy of
astandardspecimenforstandardizationthatdoesnotreflectthe stratified sampling.
entire direct measurement area of the meter, this shall be noted 6.2.3 Sample Preparation—The sample size shall be based
as the manufacturer recommendation. on the sampling principles of Practice D2915, Section 3.4,
5.2.2 The meter circuit and electrode shall be tested with based upon subsequent subdivision of the sample into sub-sets
external reference material to verify the precision and bias in for conditioning and testing. Specimen size shall be selected to
the meter response range of anticipated use.The meter shall be encompass the direct measurement region of the meter/
evaluated over the range of environmental conditions recom- electrode assembly with minimal excess material. Specimens
mended by the manufacturer. The sensitivity of this standard- must be free of visible irregularities such as knots, decay,
ization procedure to temperature of the meter shall be part of reaction wood, and resin concentrations. The specimens shall
the evaluation. be conditioned at 25 6 1°C and selected relative humidities to
5.2.2.1 The sensitivity of the standardization reference ma- each of five EMC levels between 7 and 21 % (see Guide
terial to the range of environmental conditions in 5.2.2 shall be D4933).Alternatively, specimens may be equilibrated (follow-
evaluated. ing a desorption path) at each of the five EMC conditions.
D4444 − 13 (2018)
6.2.3.1 Species—Species shall be identified. If the sample temperature probes attached, in a sealed container. The change
represents a species group, the individual species of each in indicated MC (meter indication) shall be recorded while
specimen shall be identified if anatomically possible. changing temperature through the desired range. A final meter
reading must be made at 25 6 1°C (77 6 1.8°F) to confirm
6.2.3.2 Sapwood/Heartwood—Specimensshallbechosento
that the MC has not varied from the temperature cycling.
be entirely sapwood or heartwood, or two separate groups of
(2) Standard Temperature Correction—If a laboratory de-
each, but not mixed in the same specimens. It shall be reported
termination is not made for conductance meters, the following
if sapwood/heartwood mixing is unavoidable.
relationship shall be used to correct MC below the fiber
6.2.3.3 Wood Characteristics—Specimen selection for
saturation point over the temperature range of 0 to 40°C.
wood characteristics shall be considered in setting sample size.
0.5
6.2.4 Testing—There are two steps in the testing phase of MC 5 MC 1 0.06MC T 2 25 (1)
~ !~ !
2 1 1 2
where:
calibration. The first is meter measurements on the wood
samples following the procedures of this test method and the
MC = the MC at 25°C.
applicable criteria provided by the manufacturer. The second
This information is presented in Appendix X2.
step is conducting a direct moisture content determination
following Test Methods D4442. 6.2.5.3 Correction for Chemical Additives—Meter assem-
blies applied to wood materials that have been treated with
6.2.4.1 Meter Measurement—The equilibrated specimens
additives and have adhesives interspersed with the fiber, or
are numbered, weighed, and a meter measurement taken with
both, shall be calibrated with those materials following the
the electrode aligned on the specimen in accordance with the
precepts of this and previous sections on sampling and prepa-
manufacturers recommendation. The speed of response of the
ration. Some discretion is appropriate on temperature and
meter will determine the timing of the meter reading; manu-
moisture levels, depending on the end use of the products.
facturer’s recommendations shall be followed unless this
6.2.6 Report—The following wood sample information
variable is examined as part of the calibration process.
shallberecorded:MC,size(dimensionsineachplane),species
6.2.4.2 Direct Moisture Test—The MC of each specimen
and method of species identification, sapwood/heartwood
shall be determined by the appropriate direct method (Test
percentage, density or specific gravity, growth rate (rings/25
Methods D4442) after the meter measurement. Procedures
mm) and ring orientation, and earlywood/latewood percentage.
shall be followed to prevent moisture gain or loss from the
For other materials, the appropriate wood sample information
specimens between the meter measurement and the direct test.
shall be recorded together with adequate data to identify the
6.2.5 Correction Factor Determination—The corrections
product and its constituents. The following meter information
applied to moisture meters and the precision and bias of the
shall be recorded: manufacturer and model, reference
meters may differ significantly between the technology em-
temperature, and electrode type and configuration. The follow-
ployed and manufacturing variables. Wood characteristics,
ing standardization and calibration information shall be re-
species, temperature and chemical additives are specimen
ported:methodofanalysesandpresentation,influenceofwood
variables that may require correction factors. The following
characteristics (variables), influence of temperature and
procedures shall be followed to determine correction factors
method of correction, and details of electrode placement.
for meters.
6.2.6.1 If a meter is not accompanied by the calibration data
6.2.5.1 Correction for Wood Sample Characteristics—The
of 6.2.5 or by a discussion of sensitivity of the meter to
moisture meter scale readings determined from 6.2.4.1 proce-
operating characteristics, it shall be acknowledged that the
duresshallberelatedtothecorrespondingMCfrom6.2.4.2for
influence of these operating variables is not known. Measure-
each specimen in the sample by regression or analysis of
ment of precision and bias for such a meter may have limited
variance analysis.
merit.
(1) Species calibrations that are intended to represent an
entire species (for example, to correspond to globally-
7. Presentation of Corrections and Precision and Bias
determined design values assigned to structural products) shall
Statements for Moisture Meters
be obtained only by conducting species-wide sampling.
7.1 Meters meeting the requirements of this test method
(2) The species sampling suggested in this test method is
shall have standardization procedures and corrections pre-
not required to be species-wide. Species representation claims
sented in formats that permit response to the MC, and wood
based on less-than species-wide sampling shall be correspond-
and environmental variables to which the meter may be
ingly limited.
subjected.
6.2.5.2 Correction for Wood Sample Temperature—This
7.1.1 The precision and bias of a meter may differ between
correction shall be applied after the meter has been standard-
the technology and manufacturing variables. If a meter is not
ized in accordance with Section 5 and calibrated in accordance
accompanied by the calibration data or by a discussion of
with 6.2.5.1. The options for this correction are to use a
sensitivity of the meter to operating characteristics, it shall be
standard temperature correction or to conduct a laboratory
acknowledged that the influence of these operating variables is
calibration.
notknown.Measurementofprecisionandbiasforsuchameter
(1) Determination of Temperature Correction—The correc-
may have limited merit.
tion shall be based on samples prepared as specified in 6.2.2
except that specimens of known MC (Guide D4933)at 7.2 Generic statements of precision and bias for hand-held
25 6 1°C (77 6 1.8°F) shall be placed, with electrodes and meters are not available at this time.
D4444 − 13 (2018)
8. Precision and Bias for this Test Method
8.1 Statements for the precision and bias of this test method
have not yet been developed.
APPENDIXES
(Nonmandatory Information)
X1. COMMENTARY
INTRODUCTION
The purpose of this appendix is to supply auxiliary information on the basis for and practice of this
test method. It is organized with paragraphs that correspond by section number to those in the
mandatory text; text paragraphs needing no explanation are not listed. This concept permits changes
at any time in order to keep the standard current and to improve its usefulness.
This is a laboratory test method; thus, “uses,” including field calibrations, are not considered in this
test method.
TABLE X1.1
Section Comments
1.1 Oven-dry measurements had been the basis of calibration in this test method for many years. In 2004, the oven-dry requirement following Test
Methods D4442 was replaced by reference directly to Test Methods D4442. This infers that any Test Methods D4442 method is acceptable as the
direct reference for a meter. It is anticipated that oven-dry measurement will remain the primary method; however, more flexibility was desired to
accommodate newer technologies and specimen needs.
1.2 The principal concepts of this test method as first incorporated in Test Method D2016 in 1965 and then in subsequent versions of this test
method, addressed only meters based on the change of wood conductance or dielectric properties with moisture content. Specific electrode con-
figurations were anticipated, based on early commercial use. Meters were classified as “resistance-type” and “dielectric-type”; no provisions were
made for other measurement technologies. Meters are now classified as “conductance” rather than “resistance-type,” and “capacitive-admittance”
rather than ”dielectric-type” to better reflect current understanding of the underlying physics of their function. This test method is formatted to per-
mit technologies other than conductance and capacitive-admittance, as well as combinations of technologies; no distinction is made in require-
ments. In addition, this method makes provision for specimen sizes to relate to the specific measurement technology of the meter.
4.1.1 Laboratory use of only the direct area of meter measurement is a change from using an empirical specimen size for all meters of the same ge-
neric type. Meter manufacturers need to specify the area of direct measurement of the meter; this may differ by electrode. Specimen sizes used in
calibration will differ by meter type and electrode. The resulting calibration will minimize the contribution of wood variable error in the calibration
and more uniformly reflect the measurement capability of the meter. Meters “field calibrated” may employ specimens that are different than were
used for the direct Test Methods D4442 measurement. While useful, and perhaps essential, for a specific use, this is not a basic calibration of the
meter, since the introduction of material (wood, air, support, and so forth) not tested by both techniques does not provide an accurate measure of
the meter function. Consequently, field calibration is addressed in Practice D7438.
5.2 Standardization—This is based on the direct area of measurement of the meter unless otherwise specified by the manufacturer to parallel the re-
quirements for calibration. An example is the use of external reference resistors to standardize the insulated pins of a conductance moisture me-
ter.
5.2.1 This recognizes that some meters and electrode systems, or both, may be difficult to standardize in the manner anticipated in 5.2; consequently,
the manufacturer may offer alternatives, noting they are exceptions for physical or mechanical reasons. An example is the use of external refer-
ence resistors applied to the tip of uninsulated pins to standardize a conductance moisture meter.
5.2.2 The standard reference material should be mechanically and physically stable under the environmental conditions of the standardization. It should
be non-hydroscopic and provide a minimum of one and preferably two reference points on the measurement scale. The meter should be evalu-
ated over the range of environmental conditions recommended by the manufacturer. The manufacturer should indicate (in the meter manual, on
the meter or meter scale, or on the supplied reference standard) the meter model, wood species, and the electrode configuration for which the
reference standard is valid.
5.2.3 The intention is to standardize at the temperature of use, comparing the result with the laboratory and manufacturer data, or both, on temperature
sensitivity for corrections or adjustments as needed.
6.2 Laboratory calibration is intended to provide reference data under controlled conditions which include both the wood and the ambient environmen-
tal variables.
D4444 − 13 (2018)
TABLE X1.1 Continued
Section Comments
6.2.2 Sampling design is to ensure that wood variables that influence meter performance are included in order that meter sensitivity is correctly
measured in calibration. This will permit this influence to be reported appropriately in Section 7. It may be appropriate for some meter
technologies to establish calibration points above the fiber saturation point; however, these should be analyzed separately from the data below the
fiber saturation point.
6.2.2.1 Meter sensitivity to wood variables is evaluated in the laboratory calibration. Examples of these variables are density, growth ring characteristics,
and mineral content. If these are not measured and represented adequately in analysis, the bias of the meter will be affected and the effect of
these variables cannot be applied as a correction. Wood species, wood characteristics, and the influence of site can be of sufficient importance to
justify the focus of a dedicated study. A study plan that identifies the target variables can assist in establishing the appropriate sampling and set
the variable boundaries within which the study applies.
6.2.3 Typically five subsets have been specified for the calibration; however, the complexity of the sampling and analysis may suggest more subsets or
a different experimental design. Traditionally a minimum of 75 green, flat-sawn specimens 20-mm thick by 75-mm (minimum) wide by 100-mm
along the grain were required for a given species for calibrating conductance meters. For capacitive-admittance meters, 20 or 40 thick by 125 by
125-mm specimens were specified. This sample was then divided into five groups of 15 each for conditioning and testing—one group at each of
five EMC levels. Depending on the variability of the MC reading of the meter, wood characteristics being studied and the Test Methods D4442-
measured moisture variability, or both, this requirement may be too small or too large. Practice D2915 guides the selection of sample size based
on the variability of the sample property with the goal of estimating the true mean reading of the subset within a stated amount and with confi-
dence. Typically 95 % confidence that the mean MC of a subset has been es
...