1、Designation: C1789 14 (Reapproved 2018)Standard Test Method forCalibration of Hand-Held Moisture Meters on GypsumPanels1This standard is issued under the fixed designation C1789; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method applies to the calibration of handheldmoisture meters for gypsum board, glass faced gypsum pa
3、nelsand fiber-reinforced gypsum panels by means of electricalconductance and dielectric meters. The test uses wetted testspecimens which are dried down in at least 5 steps to determinethe moisture content based on the weight loss in comparison tothe dry weight. The test also supplies the ERH values
4、for eachof the drying steps.1.2 This test method has not been evaluated for the influ-ence of paint or wall covering materials on the indicatedmoisture content of a gypsum board or panel substrate.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its us
5、e. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principle
6、s on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2C473 Test Methods for Physical Testi
7、ng of Gypsum PanelProductsC1177/C1177M Specification for Glass Mat Gypsum Sub-strate for Use as SheathingC1178/C1178M Specification for Coated Glass Mat Water-Resistant Gypsum Backing PanelC1278/C1278M Specification for Fiber-Reinforced GypsumPanelC1396/C1396M Specification for Gypsum BoardD4442 Tes
8、t Methods for Direct Moisture Content Measure-ment of Wood and Wood-Based MaterialsD4444 Test Method for Laboratory Standardization andCalibration of Hand-Held Moisture Meters2.2 ASHRAE Standard:32009 ASHRAE Handbook Fundamentals, Chapter 1 Psychrometrics, American Society of Heating, Refrigerat-ing
9、 and Air-conditioning Engineers3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 absolute humidity, dv,nthe ratio of the mass of watervapor to the total volume of the moist air sample.3.1.2 admittance, ninverse of impedance, a measure ofhow easily an electric current can flow th
10、rough a material.3.1.3 conductance meters, nconductance meters are thosethat measure predominantly ionic conductance between pointsof applied voltage, usually dc.3.1.3.1 DiscussionConductance meters generally havepins that penetrate into the material being measured. Direct-current conductance meters
11、 are commonly referred to as“resistance“ meters. Most commercial conductance meters arehigh-input impedance (about 1012), wide-range (104to1012) ohmmeters. Their scales are generally calibrated toread directly in moisture content (oven-dry mass basis) for aparticular calibration material and at a sp
12、ecific referencetemperature.3.1.4 dew-point temperature, td,nthe temperature atwhich a sample of moist air being cooled at constant pressureand moisture content reaches 100 % relative humidity.3.1.4.1 DiscussionThe dew-point temperature is the tem-perature at which water condensation begins to occur
13、 on acooled surface in contact with moist air.3.1.5 dielectric meters, nmeters that measure primarily byadmittance or power loss.1This test method is under the jurisdiction ofASTM Committee C11 on Gypsumand Related Building Materials and Systems and is the direct responsibility ofSubcommittee C11.01
14、 on Specifications and Test Methods for Gypsum Products.Current edition approved Oct. 1, 2018. Published October 2018. Originallyapproved in 2013. Last previous edition approved in 2014 as C1789 14. DOI:10.1520/C1789-14R18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orconta
15、ct ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta
16、, GA30329, http:/www.ashrae.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Princi
17、ples for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.5.1 DiscussionDielectric meters generally do not havepins that penetrate into the material being measured. There aretwo general types
18、 of dielectric meters that may be arbitrarilycategorized by their predominant mode of response admit-tance (or capacitance) and power loss. Both have surfacecontact electrodes and readout scales that are usually marked inarbitrary units. Most dielectric meters operate in the r-ffrequency range, gene
19、rally between 1 and 10 MHz.Admittancemeters respond primarily to the capacitance (dielectric con-stant) of the material being measured. Power loss meters reactprimarily to the resistance of the material. Readings of dielec-tric meters are significantly affected by the relative density(specific gravi
20、ty) of the specimen material.3.1.6 equilibrium moisture content, EMC, nthe moisturecontent of a material that is in thermodynamic equilibrium withthe surrounding air at a given temperature and relative humid-ity.3.1.7 equilibrium relative humidity, ERHthe relative hu-midity of the air in a sealed ch
21、amber that is in thermodynamicequilibrium with a sample of material in that chamber.3.1.8 humidity ratio, W, nthe ratio of the mass of watervapor to the mass of dry air contained in a sample of moist air.3.1.9 moisture content, MC, nthe ratio of the mass ofwater in a material to the oven-dry mass of
22、 the sampleexpressed as a decimal fraction or percentage.3.1.9.1 DiscussionOven-dry refers to the removal by heat-ing of all adsomcrbed and free water in the interstitial pores ofthe material. Crystalline water such as contained in gypsummolecules is not included.3.1.10 relative humidity, ,nthe rati
23、o of the amount ofwater vapor in air to the amount of water vapor in saturated airat the same temperature and pressure.3.1.10.1 DiscussionEquivalent to the ratio of the partialpressure of water vapor in the air to the saturated vaporpressure at the same temperature and pressure.3.1.11 test uncertain
24、ty ratio, TUR, ncomparison betweenthe accuracy of the Unit Under Test (UUT) and the estimatedcalibration uncertainty stated with a confidence level of 95 %(K=2).3.1.12 water activity, Aw,nthe ratio of the water vaporpressure in a material to the vapor pressure of pure water at thesame temperature.3.
25、1.12.1 DiscussionWater activity is an intrinsic propertyderived from fundamental principles of thermodynamics andphysical chemistry. It is a measure of the energy status of thewater in a system. Commonly used for food preservationanalyses, it can be interpreted here as the amount of water in aporous
26、 material that is available to impact the performancecharacteristics of the material or to support mold growth.4. Summary of Test Method4.1 These test methods provide a method for calibrating thescale on conductance and dielectric meters for various types ofgypsum boards and panels for use in field
27、measurement ofmoisture content during storage, construction and use inbuilding assemblies.4.2 The calibration is based on the MC of the test specimen.The corresponding ERH is determined by use of a calibrateddirect read relative humidity meter.4.3 ERH is essentially equivalent to water activity Awwh
28、ich is a measure of the amount of moisture in a material thatis available to impact the performance characteristics of thatmaterial.4.4 Due to the various core and/or facing additives that areused to modify the moisture absorption characteristics, strengthand/or other properties for specific applica
29、tions, a separatecalibration is required for each type of gypsum board or panelto be measured.4.5 The test method has the following steps:4.5.1 Measure the dry weights of the test specimens.4.5.2 Determine the time step for the drying intervals thatwill provide sufficient data points to develop a ca
30、librationcurve.4.5.3 Saturate the samples with water.4.5.4 Dry the samples in steps, recording after each intervalthe moisture content by weight of each sample and thetemperature, relative humidity (ERH), and absolute humidityof the atmosphere in moisture equilibrium with each sample.5. Significance
31、 and Use5.1 This Standard Test Method is intended for use incalibrating hand-held meters to accurately read from approxi-mately 30 to 90 % ERH. Moisture content is related to the ERHor water activity of a material.5.2 Hand-held meters provide a rapid means of sampling themoisture content of gypsum b
32、oards and panels during manu-facture and for field inspection during and after buildingconstruction. However, these measurements are inferential,that is, electrical parameters are measured and comparedagainst a calibration curve to obtain an indirect measure ofmoisture content. The electrical measur
33、ements are influencedby the actual moisture content, a number of other gypsumboard and panel variables, environmental conditions, the ge-ometry of the measuring probe, and the design of the meter.The maximum accuracy can only be obtained by an awarenessof the effect of each parameter on the meter ou
34、tput andcorrection of readings as specified by these test methods.5.3 Electrical conductance and dielectric meters are notnecessarily equivalent in their readings under the same condi-tions. When this test method is referenced, the type of meterthat is being used must be reported with the relevant r
35、anges forprecision and bias as specified in this standard.5.4 Both types of meters are to be calibrated with respect toERH as described in this standard.6. Apparatus6.1 Laboratory equipment for moisture content determina-tion by direct method:6.1.1 Forced Air OvenVented electric furnace capable ofma
36、intaining a steady-state temperature of 45 6 3C (113 65F).C1789 14 (2018)26.1.2 Environmental ChamberChamber capable of main-taining a controlled temperature of 20 6 2C (68 6 4F) andrelative humidity within the range 30 to 90 6 5%.6.1.3 Electronic Balance or ScaleElectronic scale capableof weighing
37、each test specimen to within 60.10 g(60.0035 oz).6.1.4 Relative Humidity Test MeterThe meter shall becapable of reading between 30 and 90 % relative humidity. Thecalibrated test uncertainty ratio (TUR) of this meter shall not beless than 4:1 over the range of measure cited.6.1.4.1 Meter shall have r
38、emovable temperature/humidityprobes that can be sealed into sealed plastic bags.6.1.5 Humidity BoxInsulated box made of materials im-pervious to water vapor such as plastic or sheet metal, sealedwith a gasketed lid. Open trays of clean, distilled water arepositioned in the box so as to keep the atmo
39、sphere within thebox saturated with water vapor. Open mesh shelving or racksare used to support samples above the water.6.1.6 Zip Sealed Plastic BagsCommercially availableplastic freezer weight plastic food storage bag with a zippertype closure that seals and prevents water vapor transmission.6.1.7
40、Psychrometric ChartGraphical presentation of thethermodynamic properties of moist air.7. Laboratory Calibration7.1 This procedure is designed for full-scale calibration ofthe meter. A minimum of 45 calibration specimens shall befabricated with a target of ten (10) calibration steps rangingfrom ERH o
41、f 30 to 90 %.NOTE 130 % relative humidity represents a practical lower limit onmoisture content found in buildings and the accuracy of readings above90 % relative humidity is problematic. The calibration should not beextrapolated below the lowest value tested or above the highest valuetested. Materi
42、al of the type to be calibrated shall be prepared and tested ina manner that is consistent with the following calibration procedures.7.2 Specimens shall be free of visible irregularities.7.3 Select a minimum of 45 specimens, each measuring100 mm wide by 200 mm long (4 by 8 in.), for each givensample
43、 of board or panel.7.3.1 The specimens shall be divided into a minimum ofthree (3) groups of 15 specimens each.7.3.2 Each specimen shall be assigned a group designationand a specimen number (for example, A-1, A-2, A-3, B-1, B-2,B-3, and so forth) and labeled with a pencil or waterproof ink.8. Determ
44、ine Dry Specimen Weights and EquilibriumHumidity Ratios8.1 Determine the dry weight of each specimen.8.1.1 Place the test specimens into forced air oven set at45C (113F). Arrange the specimens so that heated aircirculates freely around all sides of the specimens. Use racks orholders to keep the spec
45、imens separated sufficiently to allowair flow between the specimens.8.1.2 Remove and weigh each test specimen at one hourintervals.8.1.3 The test specimen is deemed to be dry when threeconsecutive weighings show no change in weight within60.10 % of the dried sample weight.8.1.4 Record the dry weight
46、 of each specimen.8.2 Determine the humidity ratio of the trapped environ-ment that is in moisture equilibrium with each specimen.NOTE 2Humidity ratio is used as the temperature is likely to varyduring the course of the test and relative humidity will vary withtemperature at constant moisture conten
47、t. Humidity ratio and dew-pointtemperature do not vary with temperature at constant moisture content andcan be calculated from the temperature and relative humidity valuesmeasured by direct read instruments.8.2.1 Place the specimen in a zip sealed plastic bag tocontain it in a trapped atmosphere.8.2
48、.2 Insert a temperature/relative humidity probe throughthe wall of the bag and seal tightly.NOTE 3Making a small slit in the side of the bag to stretch around therelative humidity probe has proven to provide a reliable seal.8.2.3 Record the temperature and relative humidity withinthe bag at one hour
49、 intervals.8.2.3.1 Calculate the humidity ratio using a psychrometricchart or a table of thermodynamic properties of moist air.8.2.3.2 Record the dry specimen temperature, relative hu-midity and humidity ratio when three consecutive measure-ments show no change in humidity ratio as calculated from themeter readings.9. Saturate the Test Specimens9.1 As the moisture level for physical damage is an ERH of80%(Awof 0.8) the test specimens must be saturated abovethis point as a starting point for calibration. The targetsaturation level is 95 % re
