ASTM D6782-02
(Test Method)Standard Test Methods for Standardization and Calibration of In-Line Dry Lumber Moisture Meters
Standard Test Methods for Standardization and Calibration of In-Line Dry Lumber Moisture Meters
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).
1.2 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 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D 6782 – 02
Standard Test Methods for
Standardization and Calibration of In-Line Dry Lumber
Moisture Meters
This standard is issued under the fixed designation D 6782; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 4444 Test Methods for Use and Calibration of Hand-Held
Moisture Meters
1.1 These test methods apply to instruments designed to
D 4933 Guide for Moisture Conditioning of Wood and
detect, or measure, moisture in wood which has been dried
Wood-Base Materials
below the fiber saturation point. The purpose of these tests is to
D 5536 Practice for Sampling Forest Trees for Determina-
provide a unified standard against which such systems can
tion of Clear Wood Properties
demonstrate their suitability for their intended use (see Appen-
dix X1).
3. Terminology
1.2 The standard is configured to support tests by moisture
3.1 Definitions of Terms Specific to This Standard:
meter manufacturers as well as end-users of such systems,
3.1.1 accept/reject meters, n—meters that permit identifica-
therefore the text follows two tracks (see Appendix X2).
tion and/or sorting of pieces into moisture content classes. The
1.3 Test methods specified for manufacturers are generally
simplest design has one set point or target level to separate
designed for laboratory settings and are intended to provide a
“wetter” from “drier” pieces. Often the meters described in
standard against which a manufacturer certifies calibration and
3.1.5 may be operated as accept/reject meters.
general system conformance.
3.1.2 field, n—an environment usually not meeting the
1.4 Test methods for end-users are generally designed for
criteria of 3.1.4. This is often a meter installation at the wood
field settings and are intended as a standardized set of
processing facility where the meter and the lumber are subject
procedures for determining the suitability of a specific machine
to the process environment of mill production.
for a particular use.
3.1.3 flow, n—a term that describes the movement and
1.5 This standard does not purport to address all of the
orientation of the piece with respect to the sensing area.
safety concerns, if any, associated with its use. It is the
3.1.3.1 longitudinal-flow—in this flow arrangement, pieces
responsibility of the user of this standard to establish appro-
pass lengthwise through the sensing area. All or some portion
priate safety and health practices and determine the applica-
of the length may be sensed.
bility of regulatory limitations prior to use.
3.1.3.2 transverse-flow—in this flow arrangement, the
2. Referenced Documents pieces pass crosswise through the sensing area. Transverse
meters frequently have more than one sensing area, conse-
2.1 ASTM Standards:
quently, the meter may sense more than one area of the piece
D 1990 Practice for Establishing Allowable Properties for
even if the entire piece is not sensed.
Visually-Graded Dimension Lumber from In-Grade Tests
3.1.4 laboratory, n—an environment under which condi-
of Full-Size Specimens
tions of temperature and moisture content can be controlled
D 2395 Test Methods for Specific Gravity of Wood and
within stated tolerances and which permit use of carefully
Wood-Base Materials
selected and controlled specimens.
D 2915 Practice for Evaluating Allowable Properties for
3.1.5 meters, n—in-line (or in process) moisture sensors
Grades of Structural Lumber
designed to respond in one pass to the moisture content of a
D 4442 Test Methods for Direct Moisture Content Measure-
piece passing the sensing area.
ment of Wood and Wood-Base Materials
3.1.5.1 Discussion—Meters are typically a system consist-
ing of one or more fixed sensing areas (termed heads) and a
processing/readout console that may be remote from the region
These test methods are under the jurisdiction of ASTM Committee D07 on
where sensing takes place. Meters may be either non-contact or
Wood and are the direct responsibility of Subcommittee D07.01 on Fundamental
contact types, and are considered nondestructive if the antici-
Test Methods and Properties.
pated performance of the product is not adversely affected by
Current edition approved April 10, 2002. Published June 2002.
Annual Book of ASTM Standards, Vol 04.10. the meter. The magnitude of the sensing area (sampling area) is
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6782–02
often regarded in processing as representative of the entire calibration. These test methods present the laboratory and the
piece, although the intended product requirements may require field as separate tracks (see Appendix X2).
alternate sampling or analysis schemes. The term “sensing 4.2.1 Laboratory Standardization and Calibration—This
region” is sometimes used in lieu of “sensing area” to portion of these test methods is intended for guidance of
encompass the three-dimensional sensing pattern of a meter. equipment manufacturers. Specific test recommendations are
Meters may have more than one sensing area; consequently, tailored to the capabilities of a laboratory environment.
the meter may independently sense more than one area of the 4.2.2 Field Standardization and Calibration—The predomi-
piece. Meters may be designed to indicate moisture content nant use of in-line meters is in production in which lumber
percentage, to operate as accept/reject instruments, or to be characteristics and environmental conditions reflect actual mill
used for both applications. processes. Field standardization and calibration is essential to
3.1.6 moisture content level, n—the moisture content at address or encompass much of the variability in production.
which products are defined as dry, or at which accept/reject
decisions are made. This level is dependent upon the specific 5. Laboratory Standardization and Calibration
grading rule, quality control requirements or product specifi-
This procedure is intended for testing of a specific model or
cation.
version of meters.
3.1.7 moisture indicators, n—meters which display or
5.1 Laboratory Standardization—Standardization shall be
record the estimated moisture content, or both. The moisture
performed on the meter to test the integrity of the meter and
content is estimated from a predetermined relationship between
sensing region. The meter shall be standardized using suitable
the meter output and moisture content determined by a
reference materials to provide at least one reference point other
standard method.
than zero on the meter readout. In transverse feed systems,
3.1.7.1 Discussion—Typical sensing principles are given in
standardization shall be performed separately for each sensing
Appendix X3.
region.
3.1.8 Standardization and Calibration:
5.1.1 Reference Specimens—These references are often rec-
3.1.8.1 standardization—the determination of the response
ommended and/or provided by the manufacturer of the meter.
of the meter to a reference material (see Appendix X4).
In absence of recommended reference specimens, materials
3.1.8.2 calibration—the determination of the relationship
shall be obtained that will provide consistent results during
between the response of a standardized meter and the moisture
testing and retesting.
content of a reference material, determined by a standard
NOTE 1—Although the references are preferably non-hygroscopic, they
method (see Appendix X4).
maybe hygroscopic if due care is used to assure consistency during
3.1.9 test modes, n—these terms describe the status of the
testing. For example, uniformly equalized clear wood specimens could be
piece during measurement.
used if stored to maintain constant moisture content.
3.1.9.1 static—the piece is stationary in the sensing area
5.1.2 Test Procedure—In the following procedure, at least
when the moisture measurement is made.
one reference specimen shall be used. Before each test, the
3.1.9.2 dynamic—the piece moves through the sensing area
meter shall be initialized by adjusting to the manufacturer’s
during measurement.
recommended initial reading with no material in the sensing
4. Significance and Use region. The static and dynamic tests are to be conducted at
room temperature (20-30°C/68-86°F). Any deviation from this
4.1 In-line meters provide a rapid means of detecting
temperature shall be documented in the report.
moisture content of lumber or wood products in processing
5.1.2.1 Positioning—The reference materials shall be posi-
(that is, on a continuous production line). Two major uses are
tioned in the sensing region as recommended by the manufac-
monitoring the performance of the drying process (air drying,
turer and consistent with the constraints of the intended or
kiln drying), and providing sorting or identification of material
recommended installation (see Appendix X6).
at predetermined levels of moisture content. These measure-
ments are inferential in the sense that physical measurements
NOTE 2—Although the procedure specifies a single position, it may be
are made and compared against calibration curves to obtain an useful to vary the position systematically to assess positional sensitivity.
The variation in position may provide information on requirements for
indirect measure of moisture content. These measurements
installation accuracy and effects from board misalignment, such as
may be influenced by one or more physical properties such as
skewing or warping.
actual moisture content (average and gradient; see Appendix
X5), density, surface moisture, chemical composition, size and 5.1.2.2 Static Standardization Test—After initializing, con-
temperature of wood. In addition, the measurements may also duct a static standardization by placing the reference material
be influenced by environmental conditions and the design in the sensing zone with the feed system disabled.
specifications of the meter. The best performance is obtained 5.1.2.3 Dynamic Standardization Test—After initializing
by an awareness of the effect of each parameter on the meter and conducting the static standardization (5.1.2), sequentially
output and correction of readings as specified by these test place each reference specimen (See 5.1.1 and Note 3) on a feed
methods. assembly outside the sensing zone. Energize the feed assembly
4.2 The two major anticipated users of these test methods to move the reference through the sensing zone at a selected
are instrument manufacturers whose primary concern is labo- constant speed. The speed selected shall be consistent with the
ratory standardization and calibration, and instrument owners intended installation. Record the meter reading (for example,
who may have a primary focus on field standardization and maximum or average) as the reference standard passes through
D6782–02
the sensing zone. Repeat the test at the selected test speeds. calibration variables in 5.2.1. Other characteristics that are to
(The more detailed procedure of the dynamic test is described be held constant shall be identified as selection criteria. One
in Appendix X7). example is the nominal thickness of the particular species for
which calibration is desired. Specimen length shall exceed the
NOTE 3—In some systems, such as longitudinal flow meters operating
dimensions of the sensing region for transverse meters and, for
at high speed, it may not be possible to conduct dynamic laboratory
longitudinal meters, be a single length unless length is a
standardization at operating speeds for practical reasons of control and
variable for which calibration is desired. The selected speci-
safety. In these situations, the static or slow speed standardization results
will necessarily be the basis for proceeding to the calibration step.
mens shall be free of visible irregularities such as knots, decay,
reaction wood, wane, and resin concentrations. These speci-
5.1.2.4 Temperature Test—The test shall be conducted at
mens shall be carefully selected to be representative for the
-20, 0, 20, 40 and 60°C (-4, 32, 68, 104 and 140°F) to
particular species and growth site. Specimens shall be chosen
determine the response of reference material, sensing heads,
to be entirely sapwood or heartwood if possible.
and console with temperature. At each temperature level, the
5.2.2.1 If density is a variable chosen for calibration,
system components shall be at specified thermal equilibrium,
evaluation requires data from a wide range of wood samples
allowing sufficient time for any temperature soak effect.
representing various density groups will be required. At a
Record the observed temperature and meter reading at each
minimum, three density groups shall be prepared.
temperature level.
5.2.2.2 Where growth site is the subject of calibration,
(1) Reference Material—With the sensing heads and con-
development of corrections will require specimens represent-
sole at ambient room temperature (20-30°C/68-86°F), condi-
ing several different growth sites. Where the desired accuracy
tion the reference material at the temperatures listed in 5.1.2.4.
of the calibration is known and the influence of site can be
Quickly insert the reference material within the electrical field
estimated, Practice D 2915 can be used to establish a sampling
of one sensing head. Repeat the measurement at each tempera-
plan.
ture level and record average readings.
5.2.2.3 If testing of meter sensitivity to presence of wet
(2) Sensing Heads—With the console at ambient room
pockets is required, it will be necessary to prepare a group of
temperature (20-30°C/68-86°F), place the sensing heads in a
specimens with well defined wet pockets (size, position with
room to cycle to temperatures listed in 5.1.2.4. Allow the
respect to a board, MC gradients) of several typical sizes and
reference specimen to remain with the sensing heads. Deter-
locations (see Appendix X8). The obtained data shall be
mine the thermal drift of each sensing head by the difference of
included in the report.
readings from those obtained in (1).
5.2.2.4 Species calibrations that are intended to represent an
(3) Console—With the sensing heads and reference material
entire species, for example, to correspond to globally-
at ambient room temperature (20-30°C/68-86ºF), cycle the
determined design values assigned to structural products, shall
console through the temperatures listed in 5.1.2.4. Determine
be obtained only by conducting species-wide sampling. Com-
the thermal drift of the console by differences in readings from
mittee D07 regards this species-wide samp
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