ASTM D4444-92(1998)e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
e1
Designation: D 4444 – 92 (Reapproved 1998)
Standard Test Methods for
Use and Calibration of Hand-Held Moisture Meters
This standard is issued under the fixed designation D 4444; 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.
This standard has been approved for use by agencies of the Department of Defense.
e NOTE— Section 11, Keywords, was added editorially in October 1998.
1. Scope D 4933 Guide for Moisture Conditioning of Wood and
Wood-Base Materials
1.1 These test methods apply to the measurement of mois-
ture content of solid wood, including veneer, and wood
3. Terminology
products containing additives, that is, chemicals or adhesives
3.1 Definitions of Terms Specific to This Standard:
(subject to conditions in 6.4 and 9.4). They also provide
3.1.1 conductance meters—Conductance meters are those
guidelines for meter use and calibration by manufacturers and
that measure predominantly ionic conductance between points
users as alternatives to ovendry measurements.
of applied voltage, usually dc. Direct-current conduct-ance
1.2 Conductance and dielectric meters are not necessarily
meters are commonly referred to as “resistance” meters. Most
equivalent in their readings under the same conditions. When
commercial conductance meters are high-input impedance
these test methods are referenced, it is assumed that either type
12 4 12
(about 10 V ), wide-range (10 to 10 V) ohmmeters. Their
of meter is acceptable unless otherwise specified. Both types of
scales are calibrated to read directly in moisture content
meters are to be calibrated with respect to moisture content on
(oven-dry mass basis) for a particular calibration species and at
an oven-dry mass basis as determined by Test Methods
a specific reference temperature. Readings of conductance
D 4442.
meters are practically independent of the relative density
1.3 The method title indicates the procedures and uses for
(specific gravity) of the specimen material.
each type of meter:
3.1.2 dielectric meters—There are two general types of
Section
dielectric meters that may be arbitrarily categorized by their
Method A Conductance Meters 5 to 7
Method B Dielectric Meters 8 to 10
predominant mode of response—power loss and admittance (or
capacitance). Both have surface contact electrodes and readout
1.4 This standard does not purport to address all of the
scales that are usually marked in arbitrary units. Most dielectric
safety concerns, if any, associated with its use. It is the
meters operate in the r-f frequency range, generally between 1
responsibility of the user of this standard to establish appro-
and 10 MHz. Admittance meters respond primarily to capaci-
priate safety and health practices and determine the applica-
tance (dielectric constant) of the material being measured.
bility of regulatory limitations prior to use.
Power loss meters react primarily to resistance of the material.
2. Referenced Documents Readings of dielectric meters are significantly affected by the
relative density (specific gravity) of the specimen material.
2.1 ASTM Standards:
D 4442 Test Methods for Direct Moisture Content Measure-
4. Significance and Use
ment of Wood and Wood-Base Materials
4.1 Hand-held meters provide a rapid means of sampling
moisture content of wood-based materials during and after
processing to maintain quality assurance and compliance with
These test methods are under the jurisdiction of ASTM Committee D-7 on
standards. However, these measurements are inferential, that
Wood and are the direct responsibility of Subcommittee D07.01 on Fundamental
is, electrical parameters are measured and compared against a
Test Methods and Properties.
These test methods replace, in part, Test Methods D 2016 (Annual Book of ASTM
calibration curve to obtain an indirect measure of moisture
Standards, Vol 04.09).
content. The electrical measurements are influenced by actual
Current edition approved Feb. 15, 1992. Published April 1992. Originally
moisture content, a number of other wood variables, environ-
published as D 4444 – 84. Last previous edition D 4444 – 84.
Annual Book of ASTM Standards, Vol 04.10. mental conditions, geometry of the measuring probe, and
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
e1
D 4444 – 92 (1998)
design of the meter. The maximum accuracy can only be to be aligned so that the current flow is parallel to the grain.
obtained by an awareness of the effect of each parameter on the Meter scale readings are to be taken and recorded immediately
meter output and correction of readings as specified by these after the electrode pins are inserted.
test methods. 5.1.2.3 Species Correction Factor Determination—The
moisture meter scale reading must be regressed against the
METHOD A—CONDUCTANCE METERS
corresponding moisture content for each specimen in the
sample by linear regression analysis. The equation for the
5. Standardization and Calibration
regression line (Y=a+bX) shall be used to establish the
5.1 Periodic standardization shall be performed on the meter
correction factor (Y−X) for meter scale readings (Y)of7to21
to test the integrity of the meter and electrode. Laboratory
inclusive.
calibration procedures are intended to provide reference data
5.1.2.4 The following wood sample information shall be
under controlled conditions that include the wood and ambient
recorded: moisture content, size (dimensions in each plane),
variables. Field calibration tests on species shall be performed
species, sapwood/heartwood percentage, relative density,
only with a meter that has been standardized and properly
growth rate (rings/25 mm), and earlywood/latewood percent-
compensated for temperature and pin configuration. Initially,
age. For other materials, the appropriate wood sample infor-
standardization should be performed before each period of use.
mation shall be recorded together with adequate data to
The time interval may be extended if experience shows that the
identify the product and its constituents. The following meter
particular meter is stable for a longer time under equivalent use
information shall be recorded: manufacturer and model, refer-
conditions.
ence temperature, applied voltage, and electrode type and
5.1.1 Standardization—The meter circuit shall be tested by
configuration.
connecting external resistors to the electrode pins, noting the
5.2 Field Calibration—Under processing conditions, labo-
corresponding MC (moisture content) value, and comparing
ratory calibration procedure is impractical, particularly because
with manufacturer’s data. At least two, and preferably three
of moisture gradients. The procedure in 5.1.2 should be applied
points shall be used to standardize the meter. The manufacturer
to develop a meaningful relationship between meter reading
shall indicate (in the manual, on the meter or meter scale, or on
and actual MC. All field calibrations must be referenced to
the supplied resistance standard) the meter model, wood
oven-dry tests to determine precision and bias. Standardization
species, and number of pins for which the resistances are valid.
procedures (5.1.1) must be followed to assure valid field
5.1.2 Laboratory Calibration—This procedure is designed
calibration at the specific field conditions during testing.
for full-scale calibration of the meter. If only a limited portion
Special care must be taken to minimize errors caused by the
of the scale requires calibration, the number of EMC (equilib-
influence of wood temperature on readings. Specimen size for
rium moisture content) levels can be reduced to as low as two.
field testing may be full size or sections thereof.
In any case, the calibration should not be extrapolated below
the lowest value. Extrapolation above 21 % EMC to the fiber
6. Conductance Meter Use
saturation point is permissible, provided a value near 21 % is
6.1 Readings:
obtained. Material other than solid wood shall be prepared and
6.1.1 Range—The range of moisture contents that can be
tested in a manner that is consistent with the following
detected by these meters is from a minimum of 6 or 7 % MC
calibration procedures. Specimen size and shape may be
to a maximum of 25 to 27 % MC (nominal value of the fiber
altered to permit testing of product-sized specimens.
saturation point). Meter scales extend above this limit only to
5.1.2.1 Test Sample Preparation—A minimum of 75 green,
permit temperature corrections of moisture contents up to the
flat-sawn specimens 20 mm thick by 75 mm (min) wide by 100
fiber saturation point, and do not imply reliability of readings
mm along the grain shall be used for a given species.
above the fiber saturation point.
Specimens must be free of visible irregularities such as knots,
decay, reaction wood, and resin concentrations (Note 1). The
NOTE 2—One use of the temperature correction is for “hot metering” of
kiln-dried lumber during which readings are taken to determine if the load
specimens shall be divided into 5 groups of 15 each and
has reached the desired endpoint MC. However, such readings are subject
conditioned at 25 6 1°C and selected relative humidities to
to considerable error because of “edge-readings,” assumptions of wood
each of five EMC levels between 7 and 21 % (see Guide
temperature, unknown moisture gradients, and temperature effects on the
D 4933). Each group will then be moisture meter tested in
meter circuitry. A further use of this correction is for moisture measure-
accordance with 5.2.2, and moisture contents determined by a
ment of dry lumber that is exposed to below-freezing temperatures. As
direct method (Test Methods D 4442). Alternatively, 15 speci-
with hot lumber, considerable errors are possible due to assumptions of
mens may be equilibrated (following a desorption path) at each
wood temperature, unknown moisture gradients, and temperature effects
on meter circuitry.
of the 5 EMC conditions.
6.1.2 Moisture Content Readings—Conductance moisture
NOTE 1—Ideally, samples shall be chosen to be entirely sapwood or
meters can be used to determine “point” moisture content
heartwood, or two separate groups of each, but not mixed in the same
specimens. In the event that sapwood/heartwood mixing is unavoidable,
directly or average moisture content indirectly. Take all read-
testing and test results shall be modified to report the effect of mixing on
ings with the pins aligned so that the current flow is parallel to
the results.
the grain. Average moisture content can be obtained through
5.1.2.2 Moisture Meter Testing—The equalized specimens the thickness by integrating moisture content versus thickness.
are numbered, weighed, and moisture meter tested at their Under the following conditions it can also be inferred from a
centers using an electrode in accordance with 6.5. The pins are single point measure.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
e1
D 4444 – 92 (1998)
6.1.2.1 Single Point Average MC Reading—Wood of rect- calibration procedures (5.2) (Note 5). Where correction data
angular cross section tends to develop a parabolic gradient are not available, calibrate the meter in accordance with
during drying (assuming that the maximum moisture content is procedure 5.2.
below FSP (fiber saturation point). From the geometry of a
NOTE 4—Species groups (such as Hem-Fir and Spruce-Pine-Fir) may
parabola, the point of average MC lies between one fourth and
contain species which cannot be visually separated at the point of moisture
one fifth of the total thickness. Therefore, if the pins are driven
measurement, or where such separation is impractical.
to this point, an approximation can be obtained for average MC
NOTE 5—For some species, or species groups, property variations
related to site or genetics may introduce discrepancies in the correction. In
of the cross section. Using the same principle, a circular cross
this case, a special calibration should be made, with emphasis on
section has its average MC at one sixth to one seventh of the
documenting the wood properties.
diameter.
6.3.2 Heartwood/Sapwood——Some species have substan-
NOTE 3—The above generalizations do not pertain if lumber has been
tial differences in meter readings for heartwood and sapwood
dried in conditions that induce steep moisture gradients (such as in drying
portions having the same actual moisture contents. In field
above 100°C) or if the lumber is known or thought to contain wet pockets
or streaks. This can be examined by driving pins to mid-thickness. measurements where these zones cannot be visually separated
or where separate heartwood/sapwood measurements are im-
6.1.3 Moisture Gradients—Unless the moisture distribution
practical, make some judgment for the correct calibration.
and measuring techniques are well understood, readings can be
6.4 Corrections For Additives:
easily misinterpreted. Four special problems should be consid-
6.4.1 Chemicals—Wood products which have been treated
ered:
with preservatives, fire retardants, or dimensional stabilization
6.1.3.1 Noninsulated electrodes (see 6.5.1).
agents may give abnormal readings (usually high). Of these
6.1.3.2 Nonparabolic gradients (see Note 3).
chemicals, creosote and pentachlorophenol solutions appear to
6.1.3.3 Surface Moisture on Electrode—Surface films of
have insignificant effects. However, salt solutions may cause
moisture, particularly from condensation on the electrode
abnormally high readings, that should be considered qualitative
(insulated pin holder) may cause larger errors. Keep electrodes
or semiquantitative at best. Conductance meters having insu-
clean, and store and use under noncondensing conditions.
lated pins can be used to measure MC of materials that have
6.1.3.4 High Surface MC on Sample—High surface MC of
been surface-treated with chemicals provided that confirmation
the material from condensation, wetting, and high relative
is made of the accuracy through direct MC determination (Test
humidity can cause excessively high readings if noninsulated
Methods D 4442).
pins are used.
NOTE 6—CCA-C treatment has been reported to be less conductive
6.1.4 Drift—Direct current conductance meters may show
than salt treatments, reducing the error of readings
...