ASTM D6782-19

Standard Test Methods for Standardization and Calibration of In-Line Dry Lumber Moisture Meters

SIGNIFICANCE AND USE
4.1 In-line meters provide a rapid means of detecting moisture content of lumber or wood products in processing (that is, on a continuous production line). Two major uses are monitoring the performance of the drying process (air drying, kiln drying), and providing sorting or identification of material at predetermined levels of moisture content. These measurements are inferential in the sense that physical measurements are made and compared against calibration curves to obtain an indirect measure of moisture content. These measurements are influenced by one or more physical properties such as actual moisture content (average and gradient; see Appendix X5), density, surface moisture, chemical composition, size, and temperature of wood. In addition, the measurements are also influenced by environmental conditions and the design specifications of the meter. The best performance is obtained by an awareness of the effect of each parameter on the meter output and correction of readings as specified by these test methods.  
4.2 The two major anticipated users of these test methods are instrument manufacturers whose primary concern is laboratory standardization and calibration, and instrument owners whose primary concern is field standardization and calibration. These test methods present the laboratory and the field as separate tracks (see Appendix X2).  
4.2.1 Laboratory Standardization and Calibration—This portion of these test methods is intended for guidance of equipment manufacturers. Specific test recommendations are tailored to the capabilities of a laboratory environment.  
4.2.2 Field Standardization and Calibration—The predominant use of in-line meters is in production in which lumber characteristics and environmental conditions reflect actual mill processes. Field standardization and calibration is essential to address or encompass much of the variability in production.
Note 1: Applications using the output of the in-line moisture meter can modify the meter...
SCOPE
1.1 These test methods apply to instruments designed to detect, or measure, moisture in wood which has been dried below the fiber saturation point. The purpose of these tests is to provide a unified standard against which such systems can demonstrate their suitability for their intended use (see Appendix X1).  
1.1.1 Sensitivity to thin layers of surface moisture such as caused by dew or brief rain exposure is not addressed by these methods. Certain applications, such as screening material for surface adhesion, require additional assessment methodology and criteria (see Appendix X5).  
1.2 The standard is configured to support tests by moisture meter manufacturers as well as end-users of such systems, therefore the text follows two tracks (see Appendix X2).  
1.3 Test methods specified for manufacturers are generally designed for laboratory settings and are intended to provide a standard against which a manufacturer certifies calibration and general system conformance.  
1.4 Test methods for end-users are generally designed for field settings and are intended as a standardized set of procedures for determining the suitability of a specific machine for a particular use.  
1.5 Applications such as lumber marking or sorting systems utilizing the output of the in-line meter are not part of this standard.  
1.6 Applications requiring sensitivity to and identification of localized wet areas are limited to general recommendations. The presence of wet-spots is the subject of Appendix X8.  
1.7 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.8 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....

General Information

• Status: Published
• Publication Date: 31-Aug-2019
• ICS: 79.040 - Wood, sawlogs and sawn timber
• Technical Committee: D07 - Wood
• Drafting Committee: D07.01 - Fundamental Test Methods and Properties

Relations

• Replaces: ASTM D6782-13 - Standard Test Methods for Standardization and Calibration of In-Line Dry Lumber Moisture Meters
• Effective Date: 01-Sep-2019
• 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 D1990-19 - Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens
• Effective Date: 01-Oct-2019
• Refers: ASTM D4444-13(2018) - Standard Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters
• Effective Date: 01-Jul-2018
• 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 D2395-14e1 - Standard Test Methods for Density and Specific Gravity (Relative Density) of Wood and Wood-Based Materials
• Effective Date: 01-May-2014
• Refers: ASTM D2395-14 - Standard Test Methods for Density and Specific Gravity (Relative Density) of Wood and Wood-Based Materials
• Effective Date: 01-May-2014
• 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 D4444-13 - Standard Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters
• Effective Date: 01-Apr-2013
• Refers: ASTM D9-12 - Standard Terminology Relating to Wood and Wood-Based Products
• Effective Date: 15-Oct-2012
• 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

Overview

ASTM D6782-19: Standard Test Methods for Standardization and Calibration of In-Line Dry Lumber Moisture Meters is a key standard published by ASTM International. This document outlines comprehensive test methods for the standardization and calibration of in-line moisture meters used to detect or measure the moisture content in lumber or wood products that have been dried below the fiber saturation point. In-line moisture meters are essential for the wood processing industry, providing rapid and non-destructive means of monitoring drying processes and sorting materials by moisture content on a continuous production line. The standard addresses both laboratory and field procedures, ensuring reliable and accurate operation across a wide range of real-world conditions.

Key Topics

• Purpose and Scope: The standard provides unified procedures to demonstrate the suitability of in-line lumber moisture meters for their intended use. It details how manufacturers and end-users should perform standardization and calibration either in the lab or in the field.
• Laboratory Standardization: Guidance is given for equipment manufacturers to test and certify calibration under controlled environmental conditions. Laboratory protocols ensure the moisture meter's accuracy for broad applications.
• Field Calibration Procedures: Tailored procedures enable instrument owners to verify meter performance under actual production conditions, which are subject to greater variability in wood characteristics and environmental factors.
• Test Specimens and Conditions: Methods specify selection, preparation, and conditioning of reference specimens, addressing the influence of wood species, density, growth site, and temperature on measurement accuracy.
• Moisture Measurement Variables: Recognition that measurement accuracy depends on multiple parameters including moisture gradients, wood density, chemical composition, surface moisture, and environmental variables. The procedures provide for corrections based on these variables.
• Limitations: The standard does not address sensitivity to thin surface moisture layers (such as dew or rain), nor does it cover systems specifically designed for highly localized wetted areas. Applications involving marking or sorting systems based on output are also outside its scope.

Applications

ASTM D6782-19 is practically valuable across several key applications within the wood products industry:

• Drying Process Monitoring: In-line moisture meters calibrated and standardized per this standard enable real-time oversight of air or kiln drying processes, ensuring lumber is processed to the correct moisture specifications.
• Quality Control in Production: The test methods support reliable sorting or identification of lumber at preset moisture content thresholds, enabling product conformity and efficient supply chain management.
• Instrument Design and Certification: Manufacturers benefit by using these standardized protocols to certify meter conformance, increasing customer confidence and supporting regulatory compliance.
• Field Verification for Mills: Mill operators and quality control teams use field calibration techniques from this standard to validate meter performance and adapt to changing process or environmental conditions.
• Basis for Claims and Operational Adjustments: Standardized measurements provide a credible basis for making product moisture claims and adjusting processes to minimize defects related to moisture variability.

Related Standards

Several ASTM standards are referenced within ASTM D6782-19 and provide foundational support for its application, including:

• ASTM D9: Terminology Relating to Wood and Wood-Based Products
• ASTM D1990: Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber
• ASTM D2395: Test Methods for Density and Specific Gravity of Wood and Wood-Based Materials
• ASTM D2915: Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
• ASTM D4442: Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• ASTM D4444: Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters
• 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 related standards collectively support the reliable standardization, calibration, and operational use of in-line dry lumber moisture meters across laboratory and production settings, reinforcing the credibility and quality assurance in the lumber industry.

Keywords: ASTM D6782-19, lumber moisture meters, in-line moisture measurement, standardization, calibration, wood products, kiln drying, quality control, moisture content, field calibration, laboratory calibration, ASTM standards.

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: D6782 − 19
Standard Test Methods for
Standardization and Calibration of In-Line Dry Lumber
Moisture Meters
This standard is issued under the fixed designation D6782; 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.
1. Scope responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 These test methods apply to instruments designed to
mine the applicability of regulatory limitations prior to use.
detect, or measure, moisture in wood which has been dried
1.9 This international standard was developed in accor-
belowthefibersaturationpoint.Thepurposeofthesetestsisto
dance with internationally recognized principles on standard-
provide a unified standard against which such systems can
ization established in the Decision on Principles for the
demonstrate their suitability for their intended use (see Appen-
Development of International Standards, Guides and Recom-
dix X1).
mendations issued by the World Trade Organization Technical
1.1.1 Sensitivity to thin layers of surface moisture such as
Barriers to Trade (TBT) Committee.
caused by dew or brief rain exposure is not addressed by these
methods. Certain applications, such as screening material for
2. Referenced Documents
surface adhesion, require additional assessment methodology
2.1 ASTM Standards:
and criteria (see Appendix X5).
D9 Terminology Relating to Wood and Wood-Based Prod-
1.2 The standard is configured to support tests by moisture
ucts
meter manufacturers as well as end-users of such systems,
D1990 Practice for Establishing Allowable Properties for
therefore the text follows two tracks (see Appendix X2).
Visually-Graded Dimension Lumber from In-Grade Tests
1.3 Test methods specified for manufacturers are generally
of Full-Size Specimens
designed for laboratory settings and are intended to provide a
D2395 TestMethodsforDensityandSpecificGravity(Rela-
standard against which a manufacturer certifies calibration and
tive Density) of Wood and Wood-Based Materials
general system conformance.
D2915 Practice for Sampling and Data-Analysis for Struc-
tural Wood and Wood-Based Products
1.4 Test methods for end-users are generally designed for
D4442 Test Methods for Direct Moisture Content Measure-
field settings and are intended as a standardized set of
ment of Wood and Wood-Based Materials
proceduresfordeterminingthesuitabilityofaspecificmachine
D4444 Test Method for Laboratory Standardization and
for a particular use.
Calibration of Hand-Held Moisture Meters
1.5 Applications such as lumber marking or sorting systems
D4933 Guide for Moisture Conditioning of Wood and
utilizing the output of the in-line meter are not part of this
Wood-Based Materials
standard.
D5536 Practice for Sampling ForestTrees for Determination
1.6 Applications requiring sensitivity to and identification
of Clear Wood Properties
of localized wet areas are limited to general recommendations.
The presence of wet-spots is the subject of Appendix X8. 3. Terminology
3.1 For definitions of terms used in this test method, refer to
1.7 The values stated in SI units are to be regarded as the
standard. The values given in parentheses are for information Terminology D9.
only.
3.2 Definitions of Terms Specific to This Standard:
1.8 This standard does not purport to address all of the
3.2.1 accept/reject meters, n—meters that permit identifica-
safety concerns, if any, associated with its use. It is the tion or sorting, or both, of pieces into moisture content classes.
3.2.1.1 Discussion—An accept/reject meter has a specific or
These test methods are under the jurisdiction of ASTM Committee D07 on
Wood and are 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 Sept. 1, 2019. Published November 2019. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2002. Last previous edition approved in 2013 as D6782 – 13. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D6782-19. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6782 − 19
preset set-point which identifies lumber with moisture contents 3.2.8 Standardization and Calibration:
higher or lower than a predefined target value of the set-point.
3.2.8.1 standardization—the determination of the response
The simplest design has one set point or target level to separate
of the meter to a reference material (see Appendix X4).
wetter from drier pieces. Often the meters described in 3.2.5
3.2.8.2 calibration—the determination of the relationship
operate as accept/reject meters.
between the response of a standardized meter and the moisture
3.2.2 field, n—an environment usually not meeting the
content of a reference material, determined by a standard
criteria of 3.2.4.
method (see Appendix X4).
3.2.2.1 Discussion—This is often a meter installation at the
3.2.9 test modes, n—these terms describe the status of the
wood processing facility where the meter and the lumber are
piece during measurement.
subject to the process environment of mill production.
3.2.9.1 static—the piece is stationary in the sensing area
3.2.3 flow, n—a term that describes the movement and
when the moisture measurement is made.
orientation of the piece with respect to the sensing area.
3.2.3.1 longitudinal-flow—in this flow arrangement, pieces
3.2.9.2 dynamic—the piece moves through the sensing area
pass lengthwise through the sensing area, with all or some
during measurement.
portion of the length being sensed.
3.2.10 wet-spots, n—localized area of moisture content
3.2.3.2 transverse-flow—in this flow arrangement, the
higher than adjacent wood, most commonly caused by infected
pieces pass crosswise through the sensing area.
wood, localized obstructions to uniform drying or non-uniform
(1) Discussion—Transverse meters frequently have more
drying characteristics of the wood (see Appendix X8).
than one sensing area, resulting in sensing of more than one
area of the piece even if the entire piece is not sensed.
4. Significance and Use
3.2.4 laboratory, n—an environment under which condi-
4.1 In-line meters provide a rapid means of detecting
tions of temperature and moisture content can be controlled
moisture content of lumber or wood products in processing
within stated tolerances and which permit use of carefully
(that is, on a continuous production line). Two major uses are
selected and controlled specimens.
monitoring the performance of the drying process (air drying,
3.2.5 meters, n—in-line (or in process) moisture sensors
kiln drying), and providing sorting or identification of material
designed to respond in one pass to the moisture content of a
at predetermined levels of moisture content. These measure-
piece passing the sensing area.
ments are inferential in the sense that physical measurements
3.2.5.1 Discussion—Meters are typically a system consist-
are made and compared against calibration curves to obtain an
ing of one or more fixed sensing areas (termed heads) and a
indirect measure of moisture content. These measurements are
processing/readout console that may be remote from the region
influenced by one or more physical properties such as actual
where sensing takes place. Meters are either non-contact or
moisture content (average and gradient; see Appendix X5),
contact types, and are considered nondestructive if the antici-
density, surface moisture, chemical composition, size, and
pated performance of the product is not adversely affected by
temperature of wood. In addition, the measurements are also
themeter.Themagnitudeofthesensingarea(samplingarea)is
influenced by environmental conditions and the design speci-
often regarded in processing as representative of the entire
fications of the meter. The best performance is obtained by an
piece, although the intended product requirements may require
awareness of the effect of each parameter on the meter output
alternate sampling or analysis schemes. The term sensing
and correction of readings as specified by these test methods.
region is sometimes used in lieu of sensing area to encompass
the three-dimensional sensing pattern of a meter. Meters may 4.2 The two major anticipated users of these test methods
have more than one sensing area; consequently, the meter may are instrument manufacturers whose primary concern is labo-
independently sense more than one area of the piece. Meters ratory standardization and calibration, and instrument owners
may be designed to indicate moisture content percentage, to
whose primary concern is field standardization and calibration.
operate as accept/reject instruments, or to be used for both These test methods present the laboratory and the field as
applications.
separate tracks (see Appendix X2).
4.2.1 Laboratory Standardization and Calibration—This
3.2.6 moisture content level, n—the moisture content at
portion of these test methods is intended for guidance of
which products are defined as dry, or at which accept/reject
decisions are made. equipment manufacturers. Specific test recommendations are
tailored to the capabilities of a laboratory environment.
3.2.6.1 Discussion—This level is dependent upon the spe-
cific grading rule, quality control requirements or product
4.2.2 Field Standardization and Calibration—The predomi-
specification
nant use of in-line meters is in production in which lumber
characteristics and environmental conditions reflect actual mill
3.2.7 moisture indicators, n—meters which display or re-
processes. Field standardization and calibration is essential to
cord the estimated moisture content, or both.
address or encompass much of the variability in production.
3.2.7.1 Discussion—The moisture content is estimated from
a predetermined relationship between the meter output and
NOTE 1—Applications using the output of the in-line moisture meter
moisture content determined by a standard method. Typical
can modify the meter output signals or have inherent response character-
sensing principles are given in Appendix X3. istics that are not representative of the meter.
D6782 − 19
5. Laboratory Standardization and Calibration and console with temperature. At each temperature level, the
system components shall be at specified thermal equilibrium,
This procedure is intended for testing of a specific model or
allowing sufficient time for any temperature soak effect.
version of meters. Record the observed temperature and meter reading at each
temperature level.
5.1 Laboratory Standardization—Standardization shall be
(1) Reference Material—With the sensing heads and con-
performed on the meter to test the integrity of the meter and
sole at ambient room temperature (20 to 30 °C⁄68 to 86 °F),
sensing region. The meter shall be standardized using suitable
condition the reference material at the temperatures listed in
referencematerialstoprovideatleastonereferencepointother
5.1.2.4. Quickly insert the reference material within the elec-
than zero on the meter readout. In transverse feed systems,
trical field of one sensing head. Repeat the measurement at
standardization shall be performed separately for each sensing
each temperature level and record average readings.
region.
(2) Sensing Heads—With the console at ambient room
5.1.1 Reference Specimens—These references are often rec-
temperature (20 to 30 °C⁄68 to 86 °F), place the sensing heads
ommended or provided, or both, by the manufacturer of the
in a room to cycle to temperatures listed in 5.1.2.4. Allow the
meter. In absence of recommended reference specimens, ma-
reference specimen to remain with the sensing heads. Deter-
terials shall be obtained that will provide consistent results
minethethermaldriftofeachsensingheadbythedifferenceof
during testing and retesting.
readings from those obtained in (1).
NOTE 2—Although the references are preferably non-hygroscopic, they
(3) Console—With the sensing heads and reference mate-
may be hygroscopic if due care is used to assure consistency during
rial at ambient room temperature (20 to 30 °C⁄68 to 86 ºF),
testing. For example, uniformly equalized clear wood specimens could be
used if stored to maintain constant moisture content. cycle the console through the temperatures listed in 5.1.2.4.
Determine the thermal drift of the console by differences in
5.1.2 Test Procedure—In the following procedure, at least
readings from those obtained in (1) and (2).
one reference specimen shall be used. Before each test, the
5.1.3 Report—The report shall include the data collected in
meter shall be initialized by adjusting to the manufacturer’s
5.1.2 together with a detailed description of the reference
recommended initial reading with no material in the sensing
materials, the method used for temperature exposure, and any
region. The static and dynamic tests are to be conducted at
room temperature (20 to 30 °C⁄68 to 86 °F). Any deviation variation from the specified procedure.
from this temperature shall be documented in the report.
5.2 Laboratory Calibration (MC Indicators)—This method
5.1.2.1 Positioning—The reference materials shall be posi-
is intended for obtaining the greatest accuracy by comparison
tioned in the sensing region as recommended by the manufac-
of the meter output to moisture content obtained gravimetri-
turer and consistent with the constraints of the intended or
cally using the oven-drying method (seeTest Methods D4442).
recommended installation (see Appendix X6).
The accuracy of the desired results must be consistent with the
NOTE 3—Although the procedure specifies a single position, it may be
indicated accuracy of the specific oven-drying procedure in
useful to vary the position systematically to assess positional sensitivity.
Test Methods D4442. Laboratory calibration procedures are
The variation in position may provide information on requirements for
intended to provide reference data under controlled conditions
installation accuracy and effects from board misalignment, such as
of wood and ambient variables.This calibration is designed for
skewing or warping.
full-scale calibration of the meter on actual wood specimens
5.1.2.2 Static Standardization Test—After initializing, con-
having uniform moisture content (see 5.2.2). Meters must be
duct a static standardization by placing the reference material
standardized (see 5.1) before being calibrated. In transverse
in the sensing zone with the feed system disabled.
feed systems, calibration shall be done separately for each
5.1.2.3 Dynamic Standardization Test—After initializing
sensing region. The calibration curve is applicable only be-
and conducting the static standardization (5.1.2), sequentially
tween the lowest and highest values tested.
place each reference specimen (see 5.1.1 and Note 4) on a feed
5.2.1 Calibration Objectives—Establish the objectives of
assembly outside the sensing zone. Energize the feed assembly
the calibration test including specimen characteristics criteria
to move the reference through the sensing zone at a selected
(for example, uniformity of moisture content, density, species,
constant speed. The speed selected shall be consistent with the
and so forth), operating speed, and environmental conditions.
intended installation. Record the meter reading (for example,
maximum or average) as the reference standard passes through 5.2.2 Specimen Selection and Preparation—Specimens
shall be selected to represent the characteristics identified as
the sensing zone. Repeat the test at the selected test speeds.
(The more detailed procedure of the dynamic test is described calibration variables in 5.2.1. Other characteristics that are to
in Appendix X7.). be held constant shall be identified as selection criteria. One
example is the nominal thickness of the particular species for
NOTE 4—In some systems, such as longitudinal flow meters operating
which calibration is desired. Specimen length shall exceed the
at high speed, it may not be possible to conduct dynamic laboratory
dimensions of the sensing region for transverse meters and, for
standardization at operating speeds for practical reasons of control and
safety. In these situations, the static or slow speed standardization results
longitudinal meters, be a single length unless length is a
will necessarily be the basis for proceeding to the calibration step.
variable for which calibration is desired. The selected speci-
5.1.2.4 Temperature Test—The test shall be conducted at mens shall be free of visible irregularities such as knots, decay,
reaction wood, wane, and resin concentrations. These speci-
-20, 0, 20, 40 and 60 °C (-4, 32, 68, 104 and 140 °F) to
determine the response of reference material, sensing heads, mens shall be carefully selected to be representative for the
D6782 − 19
positioning and response monitoring will be required. Discussion of wet
particular species and growth site. Specimens shall be chosen
spot issues is contained in Appendix X8.
to be entirely sapwood or heartwood if possible.
5.2.2.1 If density is a variable chosen for calibration,
5.2.4.3 Wood Temperature Test—Place the entire system,
evaluation requires data from a wide range of wood samples
includingthespecimenmaterial,inaroomcapableofvariation
representing various density groups will be required. At a
from -20 to 60 °C (-4 to 140 °F) (see 5.1.2.4). With the system
minimum, three density groups shall be prepared.
in equilibrium at selected temperatures between -20 and 60 °C
5.2.2.2 Where growth site is the subject of calibration,
(-4 to 140 °F), place each specimen statically within the
development of corrections will require specimens represent-
sensing area to obtain meter readings with the specimens at the
ing several different growth sites. Where the desired accuracy
exposure temperatures. Apply the results of the temperature
of the calibration is known and the influence of site can be
test, 5.1.2.4, for the drift and temperature effect corrections.
estimated, Practice D2915 can be used to establish a sampling
The thermal effect of sensors, control consoles and wood
plan.
samples must be tested independently. Place the sensors in the
5.2.2.3 If testing to determine meter sensitivity to the
temperature-controlledroomwithcablesrunningoutsideofthe
presence of wet spots is required, it will be necessary to room to the console which is equalized at room temperature.
prepareagroupofspecimenswithwell-definedwetspots(size,
Next reverse the setup with the console in the control room
position with respect to a board, MC gradients) of several whilekeepingthesensorsatroomtemperature.Finally,testthe
typical sizes and locations (see Appendix X8). The obtained
system with wood at different temperatures while the entire
data shall be included in the report. moisture detection system is equalized at room temperature.
Use 5.2.4.3 to obtain data for the total (wood plus system)
5.2.2.4 Species calibrations that are intended to represent an
entire species, for example, to correspond to globally- temperature correction. All specimens at the different EMC
levels are to be used.
determined design values assigned to structural products, shall
be obtained only by conducting species-wide sampling. Com-
5.2.5 Effect of Variables—Determination of corrections.Af-
mittee D07 regards this species-wide sampling as meeting the
ter completing 5.2.4, obtain oven-dry values of moisture
principles that guide Practice D5536 or Practice D1990,or
content (see Test Methods D4442), specific gravity (oven-dry
both. The species sampling suggested in these test methods is
mass and volume) (see Test Methods D2395) and other
not required to be species-wide. Species representation claims
specimen characteristics (see 5.2.1) for each specimen for
based on less-than species-wide sampling shall be correspond-
comparison with the meter response. Subsequent analysis can
ingly limited.
be conducted with multivariate methods that address all of the
5.2.3 Specimen Conditioning—The specimens shall be di-
chosen variables within the analysis, such as a multiple
vided into four groups of at least twelve each and equilibrated
regression, or the response of the meter can be addressed one
(following a desorption path) to four selected equilibrium
variable at a time if the covariance is not of interest. The
moisture content (EMC) levels for the applicable moisture
following paragraphs list recommended procedures.
content (MC) range (see Guide D4933). Alternately, twelve
5.2.5.1 Species—Fromthedatacollectedinthedynamictest
specimensshallbeequilibrated(followingadesorptionpath)at
(5.2.4.2), regress the readings obtained against the moisture
each of the EMC conditions (see Note 5).
contents of the specimens.
5.2.5.2 Density and Growth Site—Fromthedatacollectedin
NOTE 5—The twelve-specimen alternative lengthens the test
considerably, but may be the only practical choice under certain
the dynamic test (5.2.4.2), perform a multiple regression or
conditions, particularly when wood variable effects are to be minimized.
similar analysis, incorporating moisture content density values
or growth sites, or both, in the analysis regression model, to
5.2.4 Test Procedure—In the following procedure, the meter
permit determination of the effect of these variables density
shall be initialized (5.1.2) with no specimens in the sensing
region. The dynamic test shall be conducted at room tempera- and growth site on moisture content readings. If the multiple
regression is performed using a statistical software package,
ture.
thesignificanceoftheadditionofdensityandgrowthsitetothe
5.2.4.1 Positioning—The specimens shall be positioned in
model will be incorporated in the printed copy of the results. If
the sensing region recommended by the manufacturer and
the technique used to perform the multiple regression does not
consistentwiththeconstraintsoftheintendedorrecommended
determine the significance of added factors, then an analysis of
installation (see Appendix X6).
variance shall be performed to determine the significance
5.2.4.2 Dynamic Test—After initializing (5.1.2), obtain one
factors.
set of specimens at a specific EMC level. Sequentially place
each specimen on the feed assembly outside the sensing zone. 5.2.5.3 Temperature—From the data collected in 5.2.4.3,
Energize the feed assembly to move the specimens through the conduct an analysis, such as regression, to relate the moisture
sensing zone at a series of constant speeds selected to encom- content readings of the meter to those obtained from oven-
pass the operating range of speeds of the meter assembly. drying.
Record the meter reading (maximum or average) as the
5.2.6 Report—The report shall contain a description of
specimens pass through the sensing zone. (The more detailed
objectives selected in 5.2.1, the data collected in 5.2.3 and
procedure of the dynamic test is described in Appendix X7).
5.2.4 together with a detailed description of the specimens and
EMC levels, the corrections or adjustments determined for the
NOTE 6—Often an objective is evaluation of the dynamic response of
target variables species, density, growth site and temperature,
the meter to a localized wet area. If this is desired as part of the dynamic
calibration, modification of the specimen selection and preparation, and any deviation from the specified procedure.
D6782 − 19
5.3 Laboratory Calibration (Accept/Reject Meters)—This 5.3.3.3 Temperature Test—Place the entire system in a room
procedure is designed for the calibration of the meter at a capable of variation from -20 to 60ºC (-4 to 140 ºF). With the
specific set point or set points, for operation as an accept/reject systeminequilibriumatselectedtemperaturesbetween-20and
gauge. Moisture content values are not to be associated with 60 °C (-4 to 140 ºF), place each specimen statically within the
sensing area to obtain accept/reject readings with the speci-
specific boards sensed by such a meter except as below or
abovecertainmoisturecontentvalues.Ifsuchmoisturecontent mens at the exposure temperatures. Apply the results of the
identification is desired for individual boards, the meter shall temperature test, 5.1.2.4, for the drift and temperature effect
be calibrated as per 5.2. Meters shall be standardized (5.1) corrections. Use the results reported from 5.2.6 to obtain data
before being calibrated. In transverse feed systems, calibration to report the species and temperature effect on set point
shall be done separately for each sensing region. performance.
5.3.4 Report—The report shall contain a discussion of the
5.3.1 Calibration Objectives—Establish the objectives of
test objectives, a detailed description of the specimen moisture
the calibration test including specimen criteria (for example,
content distribution (average, variability, wet spots if
uniformity of moisture content, density, and so forth), operat-
appropriate, and so forth), the percentage of specimens that
ing speed, and environmental conditions.
were below and above the respective set points, and number of
5.3.2 Specimen Selection and Preparation—Specimens
specimens either below or above the set points, each relative to
shall be selected following the criteria of 5.2.2 to represent the
the total number of specimens tested; the species or species
nominal thicknesses of the particular species for which cali-
group;theeffectsoftemperature,densityandgrowthsiteonset
bration is desired. Specimen length shall exceed the dimen-
point stability; and any deviation from the specified procedure.
sions of the sensing region. The selected specimens shall be
free of visible irregularities such as knots, decay, reaction
6. Field Standardization and Evaluation
wood, and resin concentrations. The specimens shall be care-
fully selected to be representative of the particular species and
Laboratory standardization and evaluation shall have been
growth site. Specimens shall be chosen to be entirely sapwood
performed on the meter or on a model with similar operational
or heartwood.
characteristics before testing to the procedures of this section.
If laboratory calibration has not been carried out, this shall be
5.3.2.1 Specimen Conditioning—Prepare sufficient speci-
mens to obtain the desired degree of set point accuracy (see acknowledged when reporting the results on Section 6 tests
under 6.3.3.
Note 7). Expose the specimens to controlled conditions to
obtain equilibrium of individual pieces with minimal moisture
6.1 Field Standardization—Field standardization and evalu-
gradients, centralized about the set point value (see Guide
ation permit addressing mill conditions and specimen variables
D4933). Determine the moisture content of the pieces applying
of practical concern with installed equipment; however, field
either Test Methods D4442 or D4444. Keep the specimens
standardization is not intended to supplant laboratory standard-
wrapped in a vapor retarder material to minimize variability
ization because of its more limited scope and lack of environ-
when not being actively tested. mental control. Field evaluation does not replace laboratory
calibration but supplements with mill process and product-
NOTE 7—The number of specimens required depends on the degree of
specific data.
success in conditioning to the set point level. See Appendix X9 for an
example of selecting specimens.
NOTE 9—In many instances, field standardization and evaluation are
performed on a species group rather than specific species, and on lumber
5.3.3 Test Procedure—In the following procedure, the meter
having defects, grain deviation, and moisture gradients that are typically
shall be initialized (5.1.2) with no specimens in the sensing
foundinprocessing,andinaphysicalenvironmentdifficulttoduplicatein
region. The dynamic test is to be conducted at room tempera-
laboratory testing. Consequently, laboratory and field tests may not
ture. This procedure is intended to both adjust and evaluate the provide identical results.
accuracy of the set point(s).
6.1.1 Reference Specimens—These reference specimens or
5.3.3.1 Positioning—The specimens shall be positioned in
procedures commonly are recommended or provided, or both,
the sensing region recommended by the manufacturer and
by the manufacturer of the meter. In the absence of recom-
consistentwiththeconstraintsoftheintendedorrecommended
mended references, materials shall be obtained that will pro-
installation (see Appendix X6).
vide consistent results during testing and retesting.
5.3.3.2 Dynamic Test—Sequentially place each specimen
NOTE 10—Although the reference materials are preferably non-
from 5.3.2.1 on the feed assembly outside the sensing zone.
hygroscopic, they may be hygroscopic if due care is used to ensure
The moisture content of the specimens shall be close to the
consistency during testing. For example, uniformly equalized clear wood
accept/reject level and they shall be tested at different speeds.
specimens that are suitable may be used if stored to maintain constant
moisture content.
Energize the feed assembly to move the specimens through the
sensing zone at selected speeds. Record the accept/reject status
6.1.2 Test Procedure—In the following procedure, at least
as specimens pass through the sensing zone (see Note 6 and
one reference specimen shall be used. Before each test, the
Note 8). (The more detailed procedure of the dynamic test is
meter shall be initialized with no material in the sensing region
described in Appendix X7.)
of each sensor. The test is to be conducted at ambient
temperature and at the reference temperatures of concern in
NOTE 8—Longitudinal-type accept/reject meters may require special
field application. If the dynamic test in laboratory standardiza-
adjustments to compensate for reaction time in the readout or marker
system, particularly for specimens of non-uniform moisture content. tion (5.1.2.3) has demonstrated no speed effect, 6.1.2.2 is not
D6782 − 19
required from this procedure, unless the maximum laboratory 6.2.1 Full-piece Basis Values—To obtain a basis moisture
speed is well below that expected during production. value for comparison to full-piece moisture scanning, particu-
larly for longitudinal in-line meters, it is desirable to take
NOTE 11—If the system contains multiple sensing regions (heads) and
multiple basis readings along the length of the member and
if the data from each region is available together with the indicated
integrate these in an appropriate manner to simulate the
average value, it is preferable to compare the average output against the
full-piece scan of the in-line meter.
individual values to determine any variations from a simple average.
Likewise, if the intent is sensitivity to localized wet areas, provision to
6.3 Evaluation of Field Response (MC Indicators)—These
check each sensing region is important.
procedures are intended to provide a method to evaluate
6.1.2.1 Positioning—The reference specimens shall be po-
moisturemeasurementerrorsassociatedwithprocessedlumber
sitioned in the sensing region recommended by the manufac-
having typical moisture content levels, moisture gradients, and
turer and consistent with the constraints of the installation.The
typical physical characteristics. Meters shall be standardized
entire specimen shall always pass completely through the
(see 6.1) before being evaluated. In transverse feed systems,
sensing region (see Appendix X6).
these evaluations shall be done separately for each sensing
region.Theextrapolationofresultsbeyondtherangeofthetest
6.1.2.2 Static Standardization—Conduct a static standard-
data is not recommended. A method for evaluating selected
ization in accordance with the manufacturer’s instructions.
portions of the piece, and dynamic options for evaluating the
6.1.2.3 Dynamic Standardization Test—After initializing
whole piece are presented. Each method provides a different
and conducting the static standardization, sequentially place
set of information upon which field calibration, operational
each reference specimen on the feed assembly outside the
adjustments, product selection decisions and product moisture
sensing zone. Energize the feed assembly to move the standard
claims are based. The choice of option depends upon the
through the sensing zone at a selected constant speed. Record
inferences to be made with the results.
themeterreading(maximumoraverage)asthestandardpasses
6.3.1 Evaluation of Selected-Portion Response—This
through the sensing zone. If the feed system has variation in
method emulates the response of the meter to selected portions
speed control, repeat the test within the range of available
of lumber passing through the sensors where the wood repre-
speeds. (The more detailed procedure of the dynamic test is
sents specific characteristics. For example, no knots, limited
described in Appendix X7.)
grain distortion, and no decay might be selected as the location
NOTE 12—Safety is a paramount issue in dynamic systems, particularly
criteria. Meter response readings are taken with the lumber
in a complex mill environment. In some systems, such as longitudinal
locations meeting the criteria in the electrode position(s).
meters operating at high speed, it may not be possible to conduct field
Subsequently, basis moisture readings are made at these same
standardization at operating speeds for practical reasons of control and
locations.
safety. In these situations, static or slow speed standardization results will
necessarily be the basis for proceeding to the calibration step.
NOTE14—Theselected-portionresponseevaluationmethodmaynotbe
suitable for longitudinal flow meters in a dynamic mode.
6.2 Basis Moisture Measurement—The moisture value
against which the meter response is to be compared will 6.3.1.1 Objectives—The objective of this method is to
depend on the objectives of the test established in 6.3.1.1 or
determine the response of the in-line meter where the locations
6.3.2.1;forexample,whetheranovendryorahand-heldmeter ofmeasurementarecarefullycontrolledtobethesameforboth
reading are regarded as the basis, and whether average piece
the meter and the basis measurement against which the meter
moisture values, highest wet local reading, or readings at will be compared. Often, these locations are regarded as clear
specified areas are to be used as basis. These static moisture
wood or as areas which would be selected for moisture
readings shall be taken immediately after the meter response inspection in quality monitoring, or both. The character of the
tests are completed, in accordance with either Test Methods
wood in the selected locations shall be clearly identified as part
D4442 or D4444. Sampling is a critical element of the basis of the objectives. The uniformity and level of moisture
measurement since it is unlikely that the area examined by the
permittedthroughthecross-sectionandinthelengthandwidth
basis technique will be exactly the same as that scanned by the
in each piece shall be part of the objectives. This method does
sensor, especially if methods Test Methods D4444 are used for
not directly represent the response of the meter to characteris-
basis. Consequently, multiple readings will be required if the
tics that have been excluded from the objectives, such as
entire sensor area is to be evaluated by the basis measurement. knotholes and wane, but which are present during moisture
Another common option is to make a practical decision on a
scanning.
subset area of the sensor region to represent the moisture 6.3.1.2 Specimen Selection and Preparation—Lumber
content. This method relates to quality monitoring procedures.
specimens shall be selected to represent the objectives outlined
in 6.3.1.1. Test locations on each piece shall be identified and
NOTE 13—While basis moisture content values may be obtained in
marked. Moisture conditions meeting the objectives shall be
several different ways, depending on the meter type, equipment available,
verified using sampling of matched material with the destruc-
and degree of accuracy desired, these measurements have variability that
should be considered when calibrating an in-line meter. Total moisture tive methods of Test Methods D4442 or by examining the
values from a cross-section obtained from oven-dry measurements may
specimens using the methods of Test Methods D4444. Wood
require multiple sampling within the lumber portion in the sensing zone.
characteristic determination shall be by the grading rules
Subset samples from single or multiple reading instruments, such as
governing the grades represented in the sample.
hand-held meters may be required. Multiple measurements by either
6.3.1.3 Test Procedure—Lumber specimens shall be placed
means are recommended to obtain reasonable accuracy and to identify
unusual variations of moisture content in the specimens. in the meter such that only the designated test location (see
D6782 − 19
6.3.1.2) is actively monitored by the meter sensor. Meter consistentwiththeconstraintsoftheinstallation(seeAppendix
manufacturer recommendations shall be followed regarding X6) and the objectives of 6.3.2.1. Obtain one set of specimens
any overlap or area of sensitivity beyond the physical sensor at the variable range of interest (for example, moisture, grade,
geometry so that the chosen wood characteristics are main- and so forth). Sequentially place each specimen on the feed
tained in these areas. Tests shall include both repetitions with assembly outside the sensing zone. Record the appropriate
thesamepieceand(samedesignatedarea)forrepeatabilityand meter reading (maximum or average) as the specimens pass
multiple pieces for between-piece variability information. through the sensing zone(s). (The more detailed procedure of a
Sample size shall be determined from preliminary tests run to dynamic test is described in Appendix X7.)
obtain variability estimates; Practice D2915 and ASTM Inter-
6.3.3 Effect of Variables/Determination of Effect Of Test
national standards on precision and bias provide guidance on
Variables—Theeffectofthevariablesonmeterresponsecanbe
setting sample size on the basis of the desired quality of the
used to determine the importance of meter adjustments and to
estimate.Lackingtheabovedata,aminimumsamplesizeof20
anticipate the moisture variability in the product. Species,
is recommended; however, it is likely that a larger, carefully
temperature, and density corrections are some of the more
selected sample will be needed if many wood variables are to
common results of analyzing the effect of test variables on
be included.
meter response. Regression and analysis of variance are two
6.3.2 Full-Piece Response—The principle employed in this methodsoftenusedtodescribemeterresponse.PracticeD2915
option is to record the meter response to the lumber at the
Section 4 provides guidance on analysis, confidence
speed of operation including all wood characteristics as run, statements, and data presentation.
and relate this response to the basis moisture content reference.
6.3.3.1 Species and Site—From the data collected, a mini-
The sampling of the piece by the meter system must be
mum analysis would be a regression of the MC meter response
acknowledged; a longitudinal system will sample much of the
readings obtained against the appropriate basis moisture con-
piece along the length while a transverse system will sample
tents (determined in 6.2). Care shall be taken in representing
designated locations on the piece. In the latter case, however,
proportions of species in a species group in this analysis (see
these locations are not controlled by test objectives to certain
5.2.5.1). If site is a variable, conduct sufficient analysis to
wood characteristics but only by the mill positioning equip-
determine site effects within species.
ment.Two options are offered for analysis; these are the choice
6.3.3.2 Density—If density is a variable of interest, identi-
of two methods of selecting the sampling for the base moisture
fication of this effect within species or species groups may
measurement, one at the anticipated inspection site for quality
require special attention in analysis. In some product lines, a
monitoring; one an integration of base samples from the entire
further analysis of the effect of density within grades within a
area monitored by the in-line meter. Each option offers a
market group may also be important to calibrating the in-line
different insight into the practical use of the in-line meter.
meter.
6.3.2.1 Test Objectives—Establish the lumber or processing
6.3.4 Conclusions—The manner in which the results of
variables, or both, to be evaluated by the dynamic test and the
6.3.3 are applied shall be consistent with the objectives and
basis measurement sampling.
conduct of the test. Those conducting the test shall set the
target precision and bias goals against which the performance
NOTE 15—Examples of lumber variables that may influence the meter
ofthemeteristobemeasuredinfieldtest.Thesedecisionsmay
output include lumber size, grade, and moisture content variability due to
wet spots or gradients. Examples of processing variables may include
result in meter corrections, in process changes, or in product
operating speed and environmental conditions.
claims regarding moisture control, or combination thereof.
6.3.2.2 Specimen Selection and Preparation—Specimens Consequently, the conclusions reached from field calibration
shall be based on the goals set for performance, the objectives
shall be selected to represent the nominal thickness of the
particular species for which calibration is desired. Specimen established for the test, and the conduct and results of the test
itself.
length shall exceed the overall dimensions of the sensing
regions. The specimens shall be pre-screened to obtain a
6.3.4.1 Selected-PortionConclusions—Becausetheanalysis
sufficiently wide range of moisture content. The number of
conducted on selected-portion sampling is limited to specific
specimens shall be selected using the principles of Practice
areas defined in the test objectives, the conclusions from this
D2915 Subsection 3.4 which links the objectives of 6.3.2.1
test method are limited to the test areas and to the lumber
with the variability anticipated in order to determine the results
characteristics defined for those areas. It is the intent that the
with sufficient precision. Consequently, the sampling of mul-
resultsprovideusefulinformationontheresponseofthein-line
tiple head, transverse meters shall be considered in specimen
system to the characteristics included; it provides no informa-
preparation and test procedures. If grade is a criteria, pieces
tion on meter response to other lumber characteristics. Further,
shall be determined to be on grade by applicable rules.
if the testing is conducted only in static mode (as may be the
6.3.2.3 Test Procedure—In the following procedure, the case with longitudinal meters), the influence of dynamic
meter shall be initialized with no specimens in the sensing process variables will not be included in the analysis and shall
region. The dynamic test shall be conducted at ambient not be referenced in the conclusions.
temperature or at the reference temperatures of concern in field
6.3.4.2 Full-Piece Conclusions—The in-line meter output
application.
from this calibration method contains the meters’ dynamic
6.3.2.4 Positioning—Thespecimensshallbepassedthrough response to the characteristics of the lumber scanned.
the sensing region as recommended by the manufacturer, and Consequently, the calibration conclusions are conditional upon
D6782 − 19
the lumber characteristics as stated in the test objectives evaluationandthoseof6.1and6.3isthatmorespecimensneed
(including size, grade, moisture, and so forth, and the variabil- to be selected within close proximity to the accept/reject
ity permitted in these characteristics) plus speed of operation moisture levels selected for evaluation
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6782 − 13 D6782 − 19
Standard Test Methods for
Standardization and Calibration of In-Line Dry Lumber
Moisture Meters
This standard is issued under the fixed designation D6782; 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.
1. Scope
1.1 These test methods apply to instruments designed to detect, or measure, moisture in wood which has been dried below the
fiber saturation point. The purpose of these tests is to provide a unified standard against which such systems can demonstrate their
suitability for their intended use (see Appendix X1).
1.1.1 Sensitivity to thin layers of surface moisture such as caused by dew or brief rain exposure is not addressed by these
methods. Applications, Certain applications, such as screening material for surface adhesion, may require additional assessment
methodology and criteria (see Appendix X5).
1.2 The standard is configured to support tests by moisture meter manufacturers as well as end-users of such systems, therefore
the text follows two tracks (see Appendix X2).
1.3 Test methods specified for manufacturers are generally designed for laboratory settings and are intended to provide a
standard against which a manufacturer certifies calibration and general system conformance.
1.4 Test methods for end-users are generally designed for field settings and are intended as a standardized set of procedures for
determining the suitability of a specific machine for a particular use.
1.5 Applications such as lumber marking or sorting systems utilizing the output of the in-line meter are not part of this standard.
1.6 Applications requiring sensitivity to and identification of localized wet areas are limited to general recommendations. The
presence of wet-spots is the subject of Appendix X8.
1.7 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.8 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.9 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.
2. Referenced Documents
2.1 ASTM Standards:
D9 Terminology Relating to Wood and Wood-Based Products
D1990 Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size
Specimens
D2395 Test Methods for Density and Specific Gravity (Relative Density) of Wood and Wood-Based Materials
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-Based 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
These test methods are under the jurisdiction of ASTM Committee D07 on Wood and are the direct responsibility of Subcommittee D07.01 on Fundamental Test Methods
and Properties.
Current edition approved April 1, 2013Sept. 1, 2019. Published May 2013November 2019. Originally approved in 2002. Last previous edition approved in 20052013 as
D6782 - 05.D6782 – 13. DOI: 10.1520/D6782-13.10.1520/D6782-19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6782 − 19
D5536 Practice for Sampling Forest Trees for Determination of Clear Wood Properties
3. Terminology
3.1 For definitions of terms used in this test method, refer to Terminology D9.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 accept/reject meters, n—meters that permit identification or sorting, or both, of pieces into moisture content classes. The
simplest design has one set point or target level to separate wetter from drier pieces. Often the meters described in 3.1.5 may be
operated as accept/reject meters.
3.2.1.1 Discussion—
An accept/reject meter has a specific or preset set-point which identifies lumber with moisture contents higher or lower than a
predefined target value of the set-point. The simplest design has one set point or target level to separate wetter from drier pieces.
Often the meters described in 3.2.5 operate as accept/reject meters.
3.2.2 field, n—an environment usually not meeting the criteria of 3.1.43.2.4. This is often a meter installation at the wood
processing facility where the meter and the lumber are subject to the process environment of mill production.
3.2.2.1 Discussion—
This is often a meter installation at the wood processing facility where the meter and the lumber are subject to the process
environment of mill production.
3.2.3 flow, n—a term that describes the movement and orientation of the piece with respect to the sensing area.
3.2.3.1 longitudinal-flow—in this flow arrangement, pieces pass lengthwise through the sensing area. All area, with all or some
portion of the length may be being sensed.
3.2.3.2 transverse-flow—in this flow arrangement, the pieces pass crosswise through the sensing area. Transverse meters
frequently have more than one sensing area, consequently, the meter may sense more than one area of the piece even if the entire
piece is not sensed.
(1) Discussion—Transverse meters frequently have more than one sensing area, resulting in sensing of more than one area of
the piece even if the entire piece is not sensed.
3.2.4 laboratory, n—an environment under which conditions of temperature and moisture content can be controlled within
stated tolerances and which permit use of carefully selected and controlled specimens.
3.2.5 meters, n—in-line (or in process) moisture sensors designed to respond in one pass to the moisture content of a piece
passing the sensing area.
3.2.5.1 Discussion—
Meters are typically a system consisting of one or more fixed sensing areas (termed heads) and a processing/readout console that
may be remote from the region where sensing takes place. Meters may be are either non-contact or contact types, and are
considered nondestructive if the anticipated performance of the product is not adversely affected by the meter. The magnitude of
the sensing area (sampling area) is often regarded in processing as representative of the entire piece, although the intended product
requirements may require alternate sampling or analysis schemes. The term sensing region is sometimes used in lieu of sensing
area to encompass the three-dimensional sensing pattern of a meter. Meters may have more than one sensing area; consequently,
the meter may independently sense more than one area of the piece. Meters may be designed to indicate moisture content
percentage, to operate as accept/reject instruments, or to be used for both applications.
3.2.6 moisture content level, n—the moisture content at which products are defined as dry, or at which accept/reject decisions
are made. This level is dependent upon the specific grading rule, quality control requirements or product specification.
3.2.6.1 Discussion—
This level is dependent upon the specific grading rule, quality control requirements or product specification
3.2.7 moisture indicators, n—meters which display or record the estimated moisture content, or both. The moisture content is
estimated from a predetermined relationship between the meter output and moisture content determined by a standard method.
3.2.7.1 Discussion—
D6782 − 19
The moisture content is estimated from a predetermined relationship between the meter output and moisture content determined
by a standard method. Typical sensing principles are given in Appendix X3.
3.2.8 Standardization and Calibration:
3.2.8.1 standardization—the determination of the response of the meter to a reference material (see Appendix X4).
3.2.8.2 calibration—the determination of the relationship between the response of a standardized meter and the moisture content
of a reference material, determined by a standard method (see Appendix X4).
3.2.9 test modes, n—these terms describe the status of the piece during measurement.
3.2.9.1 static—the piece is stationary in the sensing area when the moisture measurement is made.
3.2.9.2 dynamic—the piece moves through the sensing area during measurement.
3.2.10 wet-spots, n—localized area of moisture content higher than adjacent wood, most commonly caused by infected wood,
localized obstructions to uniform drying or non-uniform drying characteristics of the wood (see Appendix X8).
4. Significance and Use
4.1 In-line meters provide a rapid means of detecting moisture content of lumber or wood products in processing (that is, on
a continuous production line). Two major uses are monitoring the performance of the drying process (air drying, kiln drying), and
providing sorting or identification of material at predetermined levels of moisture content. These measurements are inferential in
the sense that physical measurements are made and compared against calibration curves to obtain an indirect measure of moisture
content. These measurements may be are influenced by one or more physical properties such as actual moisture content (average
and gradient; see Appendix X5), density, surface moisture, chemical composition, size, and temperature of wood. In addition, the
measurements mayare also be influenced by environmental conditions and the design specifications of the meter. The best
performance is obtained by an awareness of the effect of each parameter on the meter output and correction of readings as specified
by these test methods.
4.2 The two major anticipated users of these test methods are instrument manufacturers whose primary concern is laboratory
standardization and calibration, and instrument owners who may have a primary focus onwhose primary concern is field
standardization and calibration. These test methods present the laboratory and the field as separate tracks (see Appendix X2).
4.2.1 Laboratory Standardization and Calibration—This portion of these test methods is intended for guidance of equipment
manufacturers. Specific test recommendations are tailored to the capabilities of a laboratory environment.
4.2.2 Field Standardization and Calibration—The predominant use of in-line meters is in production in which lumber
characteristics and environmental conditions reflect actual mill processes. Field standardization and calibration is essential to
address or encompass much of the variability in production.
NOTE 1—Applications using the output of the in-line moisture meter can modify the meter output signals or have inherent response characteristics that
are not representative of the meter.
4.2.3 Applications using the output of the in-line moisture meter may modify the meter output signals or have inherent response
characteristics that are not representative of the meter.
5. Laboratory Standardization and Calibration
This procedure is intended for testing of a specific model or version of meters.
5.1 Laboratory Standardization—Standardization shall be performed on the meter to test the integrity of the meter and sensing
region. The meter shall be standardized using suitable reference materials to provide at least one reference point other than zero
on the meter readout. In transverse feed systems, standardization shall be performed separately for each sensing region.
5.1.1 Reference Specimens—These references are often recommended or provided, or both, by the manufacturer of the meter.
In absence of recommended reference specimens, materials shall be obtained that will provide consistent results during testing and
retesting.
NOTE 2—Although the references are preferably non-hygroscopic, they maybe may be hygroscopic if due care is used to assure consistency during
testing. For example, uniformly equalized clear wood specimens could be used if stored to maintain constant moisture content.
5.1.2 Test Procedure—In the following procedure, at least one reference specimen shall be used. Before each test, the meter shall
be initialized by adjusting to the manufacturer’s recommended initial reading with no material in the sensing region. The static and
dynamic tests are to be conducted at room temperature (20-30°C/68-86°F). (20 to 30 °C ⁄68 to 86 °F). Any deviation from this
temperature shall be documented in the report.
5.1.2.1 Positioning—The reference materials shall be positioned in the sensing region as recommended by the manufacturer and
consistent with the constraints of the intended or recommended installation (see Appendix X6).
NOTE 3—Although the procedure specifies a single position, it may be useful to vary the position systematically to assess positional sensitivity. The
variation in position may provide information on requirements for installation accuracy and effects from board misalignment, such as skewing or warping.
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5.1.2.2 Static Standardization Test—After initializing, conduct a static standardization by placing the reference material in the
sensing zone with the feed system disabled.
5.1.2.3 Dynamic Standardization Test—After initializing and conducting the static standardization (5.1.2), sequentially place
each reference specimen (See(see 5.1.1 and Note 34) on a feed assembly outside the sensing zone. Energize the feed assembly to
move the reference through the sensing zone at a selected constant speed. The speed selected shall be consistent with the intended
installation. Record the meter reading (for example, maximum or average) as the reference standard passes through the sensing
zone. Repeat the test at the selected test speeds. (The more detailed procedure of the dynamic test is described in Appendix X7).).
NOTE 4—In some systems, such as longitudinal flow meters operating at high speed, it may not be possible to conduct dynamic laboratory
standardization at operating speeds for practical reasons of control and safety. In these situations, the static or slow speed standardization results will
necessarily be the basis for proceeding to the calibration step.
5.1.2.4 Temperature Test—The test shall be conducted at -20°C, 0°C, 20°C, 40°C and 60°C (-4°F, 32°F, 68°F, 104°F and
140°F)-20, 0, 20, 40 and 60 °C (-4, 32, 68, 104 and 140 °F) to determine the response of reference material, sensing heads, and
console with temperature. At each temperature level, the system components shall be at specified thermal equilibrium, allowing
sufficient time for any temperature soak effect. Record the observed temperature and meter reading at each temperature level.
(1) Reference Material—With the sensing heads and console at ambient room temperature (20-30°C/68-86°F), condition the
reference material at the temperatures listed in 5.1.2.4. Quickly insert the reference material within the electrical field of one
sensing head. Repeat the measurement at each temperature level and record average readings.
(1) Reference Material—With the sensing heads and console at ambient room temperature (20 to 30 °C ⁄68 to 86 °F), condition
the reference material at the temperatures listed in 5.1.2.4. Quickly insert the reference material within the electrical field of one
sensing head. Repeat the measurement at each temperature level and record average readings.
(2) Sensing Heads—With the console at ambient room temperature (20 to 30 °C ⁄68 to 86 °F), place the sensing heads in a room
to cycle to temperatures listed in 5.1.2.4. Allow the reference specimen to remain with the sensing heads. Determine the thermal
drift of each sensing head by the difference of readings from those obtained in (1).
(3) Console—With the sensing heads and reference material at ambient room temperature (20 to 30 °C ⁄68 to 86 ºF), cycle the
console through the temperatures listed in 5.1.2.4. Determine the thermal drift of the console by differences in readings from those
obtained in (1) and (2).
(2) Sensing Heads—With the console at ambient room temperature (20-30°C/68-86°F), place the sensing heads in a room to
cycle to temperatures listed in 5.1.2.4. Allow the reference specimen to remain with the sensing heads. Determine the thermal drift
of each sensing head by the difference of readings from those obtained in (1).
(3) Console—With the sensing heads and reference material at ambient room temperature (20-30°C/68-86ºF), cycle the console
through the temperatures listed in 5.1.2.4. Determine the thermal drift of the console by differences in readings from those obtained
in (1) and (2).
5.1.3 Report—The report shall include the data collected in 5.1.2 together with a detailed description of the reference materials,
the method used for temperature exposure, and any variation from the specified procedure.
5.2 Laboratory Calibration (MC Indicators)—This method is intended for obtaining the greatest accuracy by comparison of the
meter output to moisture content obtained gravimetrically using the oven-drying method (see Test Methods D4442). The accuracy
of the desired results must be consistent with the indicated accuracy of the specific oven-drying procedure in Test Methods D4442.
Laboratory calibration procedures are intended to provide reference data under controlled conditions of wood and ambient
variables,variables. This calibration is designed for full-scale calibration of the meter on actual wood specimens having uniform
moisture content (see 5.2.2). Meters must be standardized (see 5.1) before being calibrated. In transverse feed systems, calibration
shall be done separately for each sensing region. The calibration curve should neither be extrapolated below the lowest nor above
the highest valueis applicable only between the lowest and highest values tested.
5.2.1 Calibration Objectives—Establish the objectives of the calibration test including specimen characteristics criteria (for
example, uniformity of moisture content, density, species, and so forth), operating speed, and environmental conditions.
5.2.2 Specimen Selection and Preparation—Specimens shall be selected to represent the characteristics identified as calibration
variables in 5.2.1. Other characteristics that are to be held constant shall be identified as selection criteria. One example is the
nominal thickness of the particular species for which calibration is desired. Specimen length shall exceed the dimensions of the
sensing region for transverse meters and, for longitudinal meters, be a single length unless length is a variable for which calibration
is desired. The selected specimens shall be free of visible irregularities such as knots, decay, reaction wood, wane, and resin
concentrations. These specimens shall be carefully selected to be representative for the particular species and growth site.
Specimens shall be chosen to be entirely sapwood or heartwood if possible.
5.2.2.1 If density is a variable chosen for calibration, evaluation requires data from a wide range of wood samples representing
various density groups will be required. At a minimum, three density groups shall be prepared.
5.2.2.2 Where growth site is the subject of calibration, development of corrections will require specimens representing several
different growth sites. Where the desired accuracy of the calibration is known and the influence of site can be estimated, Practice
D2915 can be used to establish a sampling plan.
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5.2.2.3 If testing of to determine meter sensitivity to the presence of wet pocketsspots is required, it will be necessary to prepare
a group of specimens with well defined well-defined wet pocketsspots (size, position with respect to a board, MC gradients) of
several typical sizes and locations (see Appendix X8). The obtained data shall be included in the report.
5.2.2.4 Species calibrations that are intended to represent an entire species, for example, to correspond to globally-determined
design values assigned to structural products, shall be obtained only by conducting species-wide sampling. Committee D07 regards
this species-wide sampling as meeting the principles that guide Practice D5536 or Practice D1990, or both. The species sampling
suggested in these test methods is not required to be species-wide. Species representation claims based on less-than species-wide
sampling shall be correspondingly limited.
5.2.3 Specimen Conditioning—The specimens shall be divided into four groups of at least twelve each and equilibrated
(following a desorption path) to four selected equilibrium moisture content (EMC) levels for the applicable MC moisture content
(MC) range (see Guide D4933). Alternately, twelve specimens shall be equilibrated (following a desorption path) at each of the
EMC conditions (see Note 45).
NOTE 5—The twelve-specimen alternative lengthens the test considerably, but may be the only practical choice under certain conditions, particularly
when wood variable effects are to be minimized.
5.2.4 Test Procedure—In the following procedure, the meter shall be initialized (5.1.2) with no specimens in the sensing region.
The dynamic test shall be conducted at room temperature.
5.2.4.1 Positioning—The specimens shall be positioned in the sensing region recommended by the manufacturer and consistent
with the constraints of the intended or recommended installation (see Appendix X6).
5.2.4.2 Dynamic Test—After initializing (5.1.2), obtain one set of specimens at a specific EMC level. Sequentially place each
specimen on the feed assembly outside the sensing zone. Energize the feed assembly to move the specimens through the sensing
zone at a series of constant speeds selected to encompass the operating range of speeds of the meter assembly. Record the meter
reading (maximum or average) as the specimens pass through the sensing zone. (The more detailed procedure of the dynamic test
is described in Appendix X7).
NOTE 6—Often an objective is evaluation of the dynamic response of the meter to a localized wet area. If this is desired as part of the dynamic
calibration, modification of the specimen selection and preparation, positioning and response monitoring will be required. Discussion of wet spot issues
is contained in Appendix X8.
5.2.4.3 Wood Temperature Test—Place the entire system, including the specimen material, in a room capable of variation from
-20 to 60°C60 °C (-4 to 140°F)140 °F) (see 5.1.2.4). With the system in equilibrium at selected temperatures between -20 and
60°C60 °C (-4 to 140°F),140 °F), place each specimen statically within the sensing area to obtain meter readings with the
specimens at the exposure temperatures. Apply the results of the temperature test, 5.1.2.4, for the drift and temperature effect
corrections. The thermal effect of sensors, control consoles and wood samples must be tested independently. Place the sensors in
the temperature-controlled room with cables running outside of the room to the console which is equalized at room temperature.
Next reverse the setup with the console in the control room while keeping the sensors at room temperature. Finally, test the system
with wood at different temperatures while the entire moisture detection system is equalized at room temperature. Use 5.2.4.3 to
obtain data for the total (wood plus system) temperature correction. All specimens at the different EMC levels are to be used.
5.2.5 Effect of Variables—Determination of corrections. After completing 5.2.4, obtain oven-dry values of moisture content (see
Test Methods D4442), specific gravity (oven-dry mass and volume) (see Test Methods D2395) and other specimen characteristics
(see 5.2.1) for each specimen for comparison with the meter response. Subsequent analysis can be conducted with multivariate
methods that address all of the chosen variables within the analysis, such as a multiple regression, or the response of the meter
maycan be addressed one variable at a time if the covariance is not of interest. The following paragraphs list recommended
procedures.
5.2.5.1 Species—From the data collected in the dynamic test (5.2.4.2), regress the readings obtained against the moisture
contents of the specimens.
5.2.5.2 Density and Growth Site—From the data collected in the dynamic test (5.2.4.2), perform a multiple regression or similar
analysis, incorporating moisture content density values or growth sites, or both, in the analysis regression model, to permit
determination of the effect of these variables density and growth site on moisture content readings. If the multiple regression is
performed using a statistical software package, the significance of the addition of density and growth site to the model will be
incorporated in the printed copy of the results. If the technique used to perform the multiple regression does not determine the
significance of added factors, then an analysis of variance shall be performed to determine the significance factors.
5.2.5.3 Temperature—From the data collected in 5.2.4.3, conduct an analysis, such as regression, to relate the moisture content
readings of the meter to those obtained from oven-drying.
5.2.6 Report—The report shall contain a description of objectives selected in 5.2.1, the data collected in 5.2.3 and 5.2.4 together
with a detailed description of the specimens and EMC levels, the corrections or adjustments determined for the target variables
species, density, growth site and temperature, and any deviation from the specified procedure.
5.3 Laboratory Calibration (Accept/Reject Meters) —Meters)—This procedure is designed for the calibration of the meter at a
specific set point or set points, for operation as an accept/reject gauge. Moisture content values are not to be associated with specific
boards sensed by such a meter except as below or above certain moisture content values. If such moisture content identification
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is desired for individual boards, the meter shall be calibrated as per 5.2. Meters shall be standardized (5.1) before being calibrated.
In transverse feed systems, calibration shall be done separately for each sensing region.
5.3.1 Calibration Objectives—Establish the objectives of the calibration test including specimen criteria (for example,
uniformity of moisture content, density, and so forth), operating speed, and environmental conditions.
5.3.2 Specimen Selection and Preparation—Specimens shall be selected following the criteria of 5.2.2 to represent the nominal
thicknesses of the particular species for which calibration is desired. Specimen length shall exceed the dimensions of the sensing
region. The selected specimens shall be free of visible irregularities such as knots, decay, reaction wood, and resin concentrations.
The specimens shall be carefully selected to be representative of the particular species and growth site. Specimens shall be chosen
to be entirely sapwood or heartwood.
5.3.2.1 Specimen Conditioning—Prepare sufficient specimens to obtain the desired degree of set point accuracy (see Note 67).
Expose the specimens to controlled conditions to obtain equilibrium of individual pieces with minimal moisture gradients,
centralized about the set point value (see Guide D4933). Determine the moisture content of the pieces applying either Test Methods
D4442 or Test Methods D4444. Keep the specimens wrapped in a vapor retarder material to minimize variability when not being
actively tested.
NOTE 7—The number of specimens required depends on the degree of success in conditioning to the set point level. See Appendix X9 for an example
of selecting specimens.
5.3.3 Test Procedure—In the following procedure, the meter shall be initialized (5.1.2) with no specimens in the sensing region.
The dynamic test is to be conducted at room temperature. This procedure is intended to both adjust and evaluate the accuracy of
the set point(s).
5.3.3.1 Positioning—The specimens shall be positioned in the sensing region recommended by the manufacturer and consistent
with the constraints of the intended or recommended installation (see Appendix X6).
5.3.3.2 Dynamic Test—Sequentially place each specimen from 5.3.2.1 on the feed assembly outside the sensing zone. The
moisture content of the specimens shall be close to the accept/reject level and they shall be tested at different speeds. Energize the
feed assembly to move the specimens through the sensing zone at selected speeds. Record the accept/reject status as specimens
pass through the sensing zone (see Note 56 and Note 78). (The more detailed procedure of the dynamic test is described in
Appendix X7).)
NOTE 8—Longitudinal-type accept/reject meters may require special adjustments to compensate for reaction time in the readout or marker system,
particularly for specimens of non-uniform moisture content.
5.3.3.3 Temperature Test—Place the entire system in a room capable of variation from -20 to 60ºC (-4 to 140ºF).140 ºF). With
the system in equilibrium at selected temperatures between -20 and 60°C60 °C (-4 to 140ºF),140 ºF), place each specimen statically
within the sensing area to obtain accept/reject readings with the specimens at the exposure temperatures. Apply the results of the
temperature test, 5.1.2.4, for the drift and temperature effect corrections. Use the results reported from 5.2.6 to obtain data to report
the species and temperature effect on set point performance.
5.3.4 Report—The report shall contain a discussion of the test objectives, a detailed description of the specimen moisture
content distribution (average, variability, wet spots if appropriate, and so forth), the percentage of specimens that were below and
above the respective set points, and number of specimens either below or above the set points, each relative to the total number
of specimens tested; the species or species group; the effects of temperature, density and growth site on set point stability; and any
deviation from the specified procedure.
6. Field Standardization and Evaluation
Laboratory standardization and evaluation shall have been performed on the meter or on a model with similar operational
characteristics before testing to the procedures of this section. If laboratory calibration has not been carried out, this shall be
acknowledged when reporting the results on Section 6 tests under 6.3.3.
6.1 Field Standardization—Field standardization and evaluation permit addressing mill conditions and specimen variables of
practical concern with installed equipment; however, field standardization is not intended to supplant laboratory standardization
because of its more limited scope and lack of environmental control. Field evaluation does not replace laboratory calibration but
supplements with mill process and product-specific data.
NOTE 9—In many instances, field standardization and evaluation are performed on a species group rather than specific species, and on lumber having
defects, grain deviation, and moisture gradients that are typically found in processing, and in a physical environment difficult to duplicate in laboratory
testing. Consequently, laboratory and field tests may not provide identical results.
6.1.1 Reference Specimens—These reference specimens or procedures commonly are recommended or provided, or both, by the
manufacturer of the meter. In the absence of recommended references, materials shall be obtained that will provide consistent
results during testing and retesting.
NOTE 10—Although the reference materials are preferably non-hygroscopic, they may be hygroscopic if due care is used to ensure consistency during
testing. For example, uniformly equalized clear wood specimens that are suitable may be used if stored to maintain constant moisture content.
6.1.2 Test Procedure—In the following procedure, at least one reference specimen shall be used. Before each test, the meter shall
be initialized with no material in the sensing region of each sensor. The test is to be conducted at ambient temperature and at the
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reference temperatures of concern in field application. If the dynamic test in laboratory standardization (5.1.2.3) has demonstrated
no speed effect, 6.1.2.2 may be omittedis not required from this procedure, unless the maximum laboratory speed is well below
that expected during production.
NOTE 11—If the system contains multiple sensing regions (heads) and if the data from each region is available together with the indicated average value,
it is preferable to compare the average output against the individual values to determine any variations from a simple average. Likewise, if the intent is
sensitivity to localized wet areas, provision to check each sensing region is important.
6.1.2.1 Positioning—The reference specimens shall be positioned in the sensing region recommended by the manufacturer and
consistent with the constraints of the installation. The entire specimen shall always pass completely through the sensing region (see
Appendix X6).
6.1.2.2 Static Standardization—Conduct a static standardization in accordance with the manufacturersmanufacturer’s instruc-
tions.
6.1.2.3 Dynamic Standardization Test—After initializing and conducting the static standardization, sequentially place each
reference specimen on the feed assembly outside the sensing zone. Energize the feed assembly to move the standard through the
sensing zone at a selected constant speed. Record the meter reading (maximum or average) as the standard passes through the
sensing zone. If the feed system has variation in speed control, repeat the test within the range of available speeds. (The more
detailed procedure of the dynamic test is described in Appendix X7).)
NOTE 12—Safety is a paramount issue in dynamic systems, particularly in a complex mill environment. In some systems, such as longitudinal meters
operating at high speed, it may not be possible to conduct field standardization at operating speeds for practical reasons of control and safety. In these
situations, static or slow speed standardization results will necessarily be the basis for proceeding to the calibration step.
6.2 Basis Moisture Measurement—The moisture value against which the meter response is to be compared will depend on the
objectives of the test established in 6.3.1.1 or 6.3.2.1; for example, whether an oven dry or a hand-held meter reading are regarded
as the basis, and whether average piece moisture values, highest wet local reading, or readings at specified areas are to be used
as basis. These static moisture readings shall be taken immediately after the meter response tests are completed, in accordance with
either Test Methods D4442 or D4444. Sampling is a critical element of the basis measurement since it is unlikely that the area
examined by the basis technique will be exactly the same as that scanned by the sensor, especially if methods Test Methods D4444
are used for basis. Consequently, multiple readings will be required if the entire sensor area is to be evaluated by the basis
measurement. Another common option is to make a practical decision on a subset area of the sensor region to represent the
moisture content. This method relates to quality monitoring procedures.
NOTE 13—While basis moisture content values may be obtained in several different ways, depending on the meter type, equipment available, and
degree of accuracy desired, these measurements have variability that should be considered when calibrating an in-line meter. Total moisture values from
a cross-section obtained from oven-dry measurements may require multiple sampling within the lumber portion in the sensing zone. Subset samples from
single or multiple reading instruments, such as hand-held meters may be required. Multiple measurements by either means are recommended to obtain
reasonable accuracy and to identify unusual variations of moisture content in the specimens.
6.2.1 Full-piece Basis Values—To obtain a basis moisture value for comparison to full-piece moisture scanning, particularly for
longitudinal in-line meters, it may be is desirable to take multiple basis readings along the length of the member and integrate these
in an appropriate manner to simulate the full-piece scan of the in-line meter.
6.3 Evaluation of Field Response (MC Indicators)—These procedures are intended to provide a method to evaluate moisture
measurement errors associated with processed lumber having typical moisture content levels, moisture gradients, and typical
physical characteristics. Meters shall be standardized (see 6.1) before being evaluated. In transverse feed systems, these evaluations
shall be done separately for each sensing region. The extrapolation of results beyond the range of the test data is not recommended.
A method for evaluating selected portions of the piece, and dynamic options for evaluating the whole piece are presented. Each
method provides a different set of information upon which field calibration, operational adjustments, product selection decisions
and product moisture claims may be are based. The choice of option depends upon the inferences to be made with the results.
6.3.1 Evaluation of Selected-Portion Response—This method emulates the response of the meter to selected portions of lumber
passing through the sensors where the wood represents specific characteristics. For example, no knots, limited grain distortion, and
no decay might be selected as the location criteria. Meter response readings are taken with the lumber locations meeting the criteria
in the electrode position(s). Subsequently, basis moisture readings are made at these same locations. This response evaluation
method may not be suitable for longitudinal flow meters in a dynamic mode.
NOTE 14—The selected-portion response evaluation method may not be suitable for longitudinal flow meters in a dynamic mode.
6.3.1.1 Objectives—The objective of this method is to determine the response of the in-line meter where the locations of
measurement are carefully controlled to be the same for both the meter and the basis measurement against which the meter will
be compared. Often, these locations are regarded as clear wood or as areas which would be selected for moisture inspection in
quality monitoring, or both. The character of the wood in the selected locations shall be clearly identified as part of the objectives.
The uniformity and level of moisture permitted through the cross-section and in the length and width in each piece shall be part
of the objectives. This method does not directly represent the response of the meter to characteristics that have been excluded from
the objectives, such as knotholes and wane, but which may be are present during moisture scanning. Among the latter may be
knotholes and wane, which are often not included in the basis measurement.
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6.3.1.2 Specimen Selection and Preparation—Lumber specimens shall be selected to represent the objectives outlined in 6.3.1.1.
Test locations on each piece shall be identified and marked. Moisture conditions meeting the objectives shall be verified using
sampling of matched material with the destructive methods of Test Methods D4442 or by examining the specimens using the
methods of Test Methods D4444. Wood characteristic determination shall be by the grading rules governing the grades represented
in the sample.
6.3.1.3 Test Procedure—Lumber specimens shall be placed in the meter such that only the designated test location (see 6.3.1.2)
is actively monitored by the meter sensor. Meter manufacturer recommendations shall be followed regarding any overlap or area
of sensitivity beyond the physical sensor geometry so that the chosen wood characteristics are maintained in these areas. Tests shall
include both repetitions with the same piece and (same designated area) for repeatability and multiple pieces for between-piece
variability information. Sample size shall be determined from preliminary tests run to obtain variability estimates; Practice D2915
and ASTM International standards on precision and bias provide guidance on setting sample size on the basis of the desired quality
of the estimate. Lacking the above data, a minimum sample size of 20 is recommended; however, it is likely that a larger, carefully
selected sample will be needed if many wood variables are to be included.
6.3.2 Full-Piece Response—The principle employed in this option is to record the meter response to the lumber at the speed
of operation including all wood characteristics as run, and relate this response to the basis moisture content reference. The sampling
of the piece by the meter system must be acknowledged; a longitudinal system will sample much of the piece along the length
while a transverse system will sample designated locations on the piece. In the latter case, however, these locations are not
controlled by test objectives to certain wood characteristics but only by the mill positioning equipment. Two options are offered
for analysis; these are the choice of two methods of selecting the sampling for the base moisture measurement, one at the
anticipated inspection site for quality monitoring; one an integration of base samples from the entire area monitored by the in-line
meter. Each option offers a different insight into the practical use of the in-line meter.
6.3.2.1 Test Objectives—Establish the lumber or processing variables, or both, to be evaluated by the dynamic test and the basis
measurement sampling. Lumber variables that may influence the meter output include lumber size, grade, and moisture content
variability due to wet spots or gradients. Processing variables may include operating speed and environmental conditions.
NOTE 15—Examples of lumber variables that may influence the meter output include lumber size, grade, and moisture content variability due to wet
spots or gradients. Examples of processing variables may include operating speed and environmental conditions.
6.3.2.2 Specimen Selection and Preparation—Specimens shall be selected to represent the nominal thickness of the particular
species for which calibration is desired. Specimen length shall exceed the overall dimensions of the sensing regions. The specimens
shall be pre-screened to obtain a sufficiently wide range of moisture content. The number of specimens shall be selected using the
principles of Practice D2915 SectionSubsection 3.4 which links the objectives of 6.3.2.1 with the variability anticipated in order
to determine the results with sufficient precision. Consequently, the sampling of multiple head, transverse meters shouldshall be
considered in specimen preparation and test procedures. If grade is a criteria, pieces shall be determined to be on grade by
applicable rules.
6.3.2.3 Test Procedure—In the following procedure, the meter shall be initialized with no specimens in the sensing region. The
dynamic test shall be conducted at ambient temperature or at the reference temperatures of concern in field application.
6.3.2.4 Positioning—The specimens shall be passed through the sensing region as recommended by the manufacturer, and
consistent with the constraints of the installation (see Appendix X6) and the objectives of 6.3.2.1. Obtain one set of specimens at
the variable range of interest (for example, moisture, grade, and so forth). Sequentially place each specimen on the feed assembly
outside the sensing zone. Record the appropriate meter reading (maximum or average) as the specimens pass through the sensing
zone(s). (The more detailed procedure of a dynamic test is described in Appendix X7.)
6.3.3 Effect of Variables/Determination of Effect Of Test Variables—The effect of the va
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