ASTM C1789-13
(Test Method)Standard Test Method for Use and Calibration of Hand-Held Moisture Meters on Gypsum Panels
Standard Test Method for Use and Calibration of Hand-Held Moisture Meters on Gypsum Panels
SIGNIFICANCE AND USE
5.1 This Standard Test Method is intended for use in calibrating hand-held meters to accurately read from approximately 30% to 90% ERH. Moisture content is related to the ERH or water activity of a material.
5.2 Hand-held meters provide a rapid means of sampling the moisture content of gypsum boards and panels during manufacture and for field inspection during and after building construction. However, these measurements are inferential, that is, electrical parameters are measured and compared against a calibration curve to obtain an indirect measure of moisture content. The electrical measurements are influenced by the actual moisture content, a number of other gypsum board and panel variables, environmental conditions, the geometry of the measuring probe, and the design of the meter. The maximum accuracy can only be obtained by an awareness of the effect of each parameter on the meter output and correction of readings as specified by these test methods.
5.3 Electrical conductance and dielectric meters are not necessarily equivalent in their readings under the same conditions. When this test method is referenced, the type of meter that is being used must be reported with the relevant ranges for precision and bias as specified in this standard.
5.4 Both types of meters are to be calibrated with respect to ERH as described in this standard.
SCOPE
1.1 This test method applies to the calibration of handheld moisture meters for gypsum board, glass faced gypsum panels and fiber-reinforced gypsum panels by means of electrical conductance and dielectric meters. The test uses wetted test specimens which are dried down in at least 5 steps to determine the moisture content based on the weight loss in comparison to the dry weight. The test also supplies the ERH values for each of the drying steps.
1.2 This test method applies to the field use of hand-held moisture meters at storage and distribution facilities, construction job sites and in buildings.
1.3 This test method has not been evaluated for the influence of paint or wall covering materials on the indicated moisture content of a gypsum board or panel substrate.
1.4 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: C1789 − 13
StandardTest Method for
Use and Calibration of Hand-Held Moisture Meters on
Gypsum Panels
This standard is issued under the fixed designation C1789; 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 ment of Wood and Wood-Base Materials
D4444 Test Method for Laboratory Standardization and
1.1 This test method applies to the calibration of handheld
Calibration of Hand-Held Moisture Meters
moisture meters for gypsum board, glass faced gypsum panels
2.2 ASHRAE Standard:
and fiber-reinforced gypsum panels by means of electrical
2009 ASHRAE Handbook – Fundamentals, Chapter 1 –
conductance and dielectric meters. The test uses wetted test
Psychrometrics,American Society of Heating, Refrigerat-
specimenswhicharedrieddowninatleast5stepstodetermine
ing and Air-conditioning Engineers
the moisture content based on the weight loss in comparison to
the dry weight. The test also supplies the ERH values for each
3. Terminology
of the drying steps.
3.1 Definitions of Terms Specific to This Standard:
1.2 This test method applies to the field use of hand-held
3.1.1 absolute humidity, d —the ratio of the mass of water
v
moisture meters at storage and distribution facilities, construc-
vapor to the total volume of the moist air sample.
tion job sites and in buildings.
3.1.2 admittance—inverse of impedance, a measure of how
1.3 This test method has not been evaluated for the influ-
easily an electric current can flow through a material.
ence of paint or wall covering materials on the indicated
3.1.3 conductance meters—conductance meters are those
moisture content of a gypsum board or panel substrate.
that measure predominantly ionic conductance between points
1.4 This standard does not purport to address all of the
of applied voltage, usually dc.
safety concerns, if any, associated with its use. It is the
3.1.3.1 Discussion—Conductance meters generally have
responsibility of the user of this standard to establish appro-
pins that penetrate into the material being measured. Direct-
priate safety and health practices and determine the applica-
current conductance meters are commonly referred to as
bility of regulatory limitations prior to use.
"resistance" meters. Most commercial conductance meters are
12 4 12
high-input impedance (about 10 Ω), wide-range (10 to 10
2. Referenced Documents
Ω) ohmmeters. Their scales are generally calibrated to read
2.1 ASTM Standards:
directly in moisture content (oven-dry mass basis) for a
C473 Test Methods for Physical Testing of Gypsum Panel
particular calibration material and at a specific reference
Products
temperature.
C1177 Specification for Glass Mat Gypsum Substrate for
3.1.4 dew-point temperature, t —the temperature at which a
d
Use as Sheathing
sample of moist air being cooled at constant pressure and
C1178 Specification for Coated Glass Mat Water-Resistant
moisture content reaches 100 percent relative humidity.
Gypsum Backing Panel
3.1.4.1 Discussion—The dew-point temperature is the tem-
C1278 Specification for Fiber-Reinforced Gypsum Panel
perature at which water condensation begins to occur on a
C1396 Specification for Gypsum Board
cooled surface in contact with moist air.
D4442 Test Methods for Direct Moisture Content Measure-
3.1.5 dielectric meters—meters that measure primarily by
admittance or power loss.
1 3.1.5.1 Discussion—Dielectric meters generally do not have
ThistestmethodisunderthejurisdictionofASTMCommitteeC11onGypsum
and Related Building Materials and Systems and is the direct responsibility of pins that penetrate into the material being measured. There are
Subcommittee C11.01 on Specifications and Test Methods for Gypsum Products.
two general types of dielectric meters that may be arbitrarily
Current edition approved Dec. 1, 2013. Published January 2014. DOI: 10.1520/
C1789-13.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Available from American Society of Heating, Refrigerating, and Air-
Standards volume information, refer to the standard’s Document Summary page on Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA
the ASTM website. 30329, http://www.ashrae.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1789 − 13
categorized by their predominant mode of response – admit- 4.3 ERH is essentially equivalent to water activity Aw
tance (or capacitance) and power loss. Both have surface which is a measure of the amount of moisture in a material that
contactelectrodesandreadoutscalesthatareusuallymarkedin is available to impact the performance characteristics of that
arbitrary units. Most dielectric meters operate in the r-f material.
frequencyrange,generallybetween1and10MHz.Admittance
4.4 Due to the various core and/or facing additives that are
meters respond primarily to the capacitance (dielectric con-
usedtomodifythemoistureabsorptioncharacteristics,strength
stant) of the material being measured. Power loss meters react
and/or other properties for specific applications, a separate
primarily to the resistance of the material. Readings of dielec-
calibration is required for each type of gypsum board or panel
tric meters are significantly affected by the relative density
to be measured.
(specific gravity) of the specimen material.
4.5 The test method has the following steps:
3.1.6 equilibrium moisture content, EMC—the moisture
4.5.1 Measure the dry weights of the test specimens.
contentofamaterialthatisinthermodynamicequilibriumwith
4.5.2 Determine the time step for the drying intervals that
the surrounding air at a given temperature and relative humid-
will provide sufficient data points to develop a calibration
ity.
curve.
3.1.7 equilibrium relative humidity, ERH—the relative hu-
4.5.3 Saturate the samples with water.
midity of the air in a sealed chamber that is in thermodynamic
4.5.4 Dry the samples in steps, recording after each interval
equilibrium with a sample of material in that chamber.
the moisture content by weight of each sample and the
3.1.8 humidity ratio, W—the ratio of the mass of water
temperature, relative humidity (ERH), and absolute humidity
vapor to the mass of dry air contained in a sample of moist air.
of the atmosphere in moisture equilibrium with each sample.
3.1.9 moisture content, MC—the ratio of the mass of water
in a material to the oven-dry mass of the sample expressed as
5. Significance and Use
a decimal fraction or percentage.
5.1 This Standard Test Method is intended for use in
3.1.9.1 Discussion—Oven-dryreferstotheremovalbyheat-
calibrating hand-held meters to accurately read from approxi-
ing of all adsomcrbed and free water in the interstitial pores of
mately 30% to 90% ERH. Moisture content is related to the
the material. Crystalline water such as contained in gypsum
ERH or water activity of a material.
molecules is not included.
5.2 Hand-heldmetersprovidearapidmeansofsamplingthe
3.1.10 relative humidity, ϕ—the ratio of the amount of water
moisture content of gypsum boards and panels during manu-
vapor in air to the amount of water vapor in saturated air at the
facture and for field inspection during and after building
same temperature and pressure.
construction. However, these measurements are inferential,
3.1.10.1 Discussion—Equivalent to the ratio of the partial
that is, electrical parameters are measured and compared
pressure of water vapor in the air to the saturated vapor
against a calibration curve to obtain an indirect measure of
pressure at the same temperature and pressure.
moisture content. The electrical measurements are influenced
3.1.11 test uncertainty ratio, TUR—comparisonbetweenthe
by the actual moisture content, a number of other gypsum
accuracy of the Unit Under Test (UUT) and the estimated
board and panel variables, environmental conditions, the ge-
calibration uncertainty stated with a confidence level of 95%
ometry of the measuring probe, and the design of the meter.
(K=2).
The maximum accuracy can only be obtained by an awareness
3.1.12 water activity, A —the ratio of the water vapor
w of the effect of each parameter on the meter output and
pressure in a material to the vapor pressure of pure water at the
correction of readings as specified by these test methods.
same temperature.
5.3 Electrical conductance and dielectric meters are not
3.1.12.1 Discussion—Water activity is an intrinsic property
necessarily equivalent in their readings under the same condi-
derived from fundamental principles of thermodynamics and
tions. When this test method is referenced, the type of meter
physical chemistry. It is a measure of the energy status of the
that is being used must be reported with the relevant ranges for
water in a system. Commonly used for food preservation
precision and bias as specified in this standard.
analyses, it can be interpreted here as the amount of water in a
porous material that is available to impact the performance
5.4 Both types of meters are to be calibrated with respect to
characteristics of the material or to support mold growth.
ERH as described in this standard.
4. Summary of Test Method
6. Apparatus
4.1 These test methods provide a method for calibrating the
6.1 Laboratory equipment for moisture content determina-
scale on conductance and dielectric meters for various types of
tion by direct method:
gypsum boards and panels for use in field measurement of
6.1.1 Forced Air Oven—Vented electric furnace capable of
moisture content during storage, construction and use in
maintaining a steady-state temperature of 45 63°C(113 6 5
building assemblies.
°F).
4.2 The calibration is based on the MC of the test specimen. 6.1.2 Environmental Chamber—Chamber capable of main-
The corresponding ERH is determined by use of a calibrated taining a controlled temperature of 20 62ºC(68 6 4 ºF) and
direct read relative humidity meter. relative humidity within the range 30% to 90% 6 5%.
C1789 − 13
NOTE 2—Humidity ratio is used as the temperature is likely to vary
6.1.3 Electronic Balance or Scale—Electronic scale capable
during the course of the test and relative humidity will vary with
of weighing each test specimen to within 6 0.10 g (6 0.0035
temperature at constant moisture content. Humidity ratio and dew-point
oz).
temperaturedonotvarywithtemperatureatconstantmoisturecontentand
6.1.4 Relative Humidity Test Meter—The meter shall be
can be calculated from the temperature and relative humidity values
capable of reading between 30% and 90% relative humidity.
measured by direct read instruments.
The calibrated test uncertainty ratio (TUR) of this meter shall
8.2.1 Place the specimen in a zip sealed plastic bag to
not be less than 4:1 over the range of measure cited.
contain it in a trapped atmosphere.
6.1.4.1 Meter shall have removable temperature/humidity
8.2.2 Insert a temperature/relative humidity probe through
probes that can be sealed into sealed plastic bags.
the wall of the bag and seal tightly.
6.1.5 Humidity Box—Insulated box made of materials im-
NOTE 3—Making a small slit in the side of the bag to stretch around the
pervious to water vapor such as plastic or sheet metal, sealed
relative humidity probe has proven to provide a reliable seal.
with a gasketed lid. Open trays of clean, distilled water are
positioned in the box so as to keep the atmosphere within the 8.2.3 Record the temperature and relative humidity within
the bag at one hour intervals.
box saturated with water vapor. Open mesh shelving or racks
are used to support samples above the water. 8.2.3.1 Calculate the humidity ratio using a psychrometric
6.1.6 Zip Sealed Plastic Bags—Commercially available chart or a table of thermodynamic properties of moist air.
plastic freezer weight plastic food storage bag with a zipper 8.2.3.2 Record the dry specimen temperature, relative hu-
type closure that seals and prevents water vapor transmission.
midity and humidity ratio when three consecutive measure-
6.1.7 Psychrometric Chart—Graphical presentation of the ments show no change in humidity ratio as calculated from the
thermodynamic properties of moist air.
meter readings.
7. Laboratory Calibration 9. Saturate the Test Specimens
7.1 This procedure is designed for full-scale calibration of
9.1 As the moisture level for physical damage is an ERH of
the meter. A minimum of 45 calibration specimens shall be
80% (A of 0.8) the test specimens must be saturated above
w
fabricated with a target of ten (10) calibration steps ranging
this point as a starting point for calibration. The target
from ERH of 30% to 90%. saturation level is 95% relative humidity at 20 °C (68 °F).
NOTE 1—30% relative humidity represents a practical lower limit on
9.2 Place specimens in a water vapor saturated atmosphere
moisture content found in buildings and the accuracy of readings above
in an environmental chamber or humidity cabinet with relative
90% relative humidity is problematic. The calibration should not be
extrapolated below the lowest value tested or above the highest value humidity equal to or greater than 95% at 20°C (68°F).
tested. Material of the type to be calibrated shall be prepared and tested in
9.2.1 Document the environmental chamber conditions us-
a manner that is consistent with the following calibration procedures.
ing a calibrated relative humidity sensor.
7.2 Specimens shall be free of visible irregularities.
9.3 Maintain specimens in the water saturated atmosphere
7.3 Select a minimum of 45 specimens, each measuring 100
until they reach moisture equilibrium with the atmosphere.
mm wide by 200 mm long (4 in. by 8 in.), for each given
9.3.1 Maintain specimens in chamber or cabinet until rela-
sample of board or panel.
tive humidity stabilizes at a reading of 95% or greater.
7.3.1 The specimens shall be divided into a minimum of
9.3.2 Remove each specimen and weigh at eight (8) hour
three (3) groups of 15 specimens each.
intervals.
7.3.2 Each specimen shall be assigned a group designation
9.3.2.1 Determine the weight of water in the specimen by
and a specimen number (e.g., A-1, A-2, A-3, B-1, B-2, B-3,
subtracting the dry weight of the sample as determined
etc.) and labeled with a pencil or waterproof ink.
according to Section 8 above.
9.3.2.2 Calculate the specimen moisture content by dividing
8. Determine Dry Specimen Weights and Equilibrium
the weight of water in the sample by the dry weight of the
Humidity Ratios
sample and
...
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