1、Designation: C1789 13Standard Test Method forUse and Calibration of Hand-Held Moisture Meters onGypsum Panels1This 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 year of la
2、st 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 panelsand fi
3、ber-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 for eachof
4、 the drying steps.1.2 This test method applies to the field use of hand-heldmoisture meters at storage and distribution facilities, construc-tion job sites and in buildings.1.3 This test method has not been evaluated for the influ-ence of paint or wall covering materials on the indicatedmoisture con
5、tent of a gypsum board or panel substrate.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulator
6、y limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C473 Test Methods for Physical Testing of Gypsum PanelProductsC1177 Specification for Glass Mat Gypsum Substrate forUse as SheathingC1178 Specification for Coated Glass Mat Water-ResistantGypsum Backing PanelC1278 Specification fo
7、r Fiber-Reinforced Gypsum PanelC1396 Specification for Gypsum BoardD4442 Test Methods for Direct Moisture Content Measure-ment of Wood and Wood-Base MaterialsD4444 Test Method for Laboratory Standardization andCalibration of Hand-Held Moisture Meters2.2 ASHRAE Standard:32009 ASHRAE Handbook Fundamen
8、tals, Chapter 1 Psychrometrics, American Society of Heating, Refrigerat-ing and Air-conditioning Engineers3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 absolute humidity, dvthe ratio of the mass of watervapor to the total volume of the moist air sample.3.1.2 admittanceinvers
9、e of impedance, a measure of howeasily an electric current can flow through a material.3.1.3 conductance metersconductance meters are thosethat measure predominantly ionic conductance between pointsof applied voltage, usually dc.3.1.3.1 DiscussionConductance meters generally havepins that penetrate
10、into the material being measured. Direct-current conductance meters are commonly referred to as“resistance“ meters. Most commercial conductance meters arehigh-input impedance (about 1012), wide-range (104to 1012) ohmmeters. Their scales are generally calibrated to readdirectly in moisture content (o
11、ven-dry mass basis) for aparticular calibration material and at a specific referencetemperature.3.1.4 dew-point temperature, tdthe temperature at which asample of moist air being cooled at constant pressure andmoisture content reaches 100 percent relative humidity.3.1.4.1 DiscussionThe dew-point tem
12、perature is the tem-perature at which water condensation begins to occur on acooled surface in contact with moist air.3.1.5 dielectric metersmeters that measure primarily byadmittance or power loss.3.1.5.1 DiscussionDielectric meters generally do not havepins that penetrate into the material being m
13、easured. There aretwo general types of dielectric meters that may be arbitrarily1This test method is under the jurisdiction ofASTM Committee C11 on Gypsumand Related Building Materials and Systems and is the direct responsibility ofSubcommittee C11.01 on Specifications and Test Methods for Gypsum Pr
14、oducts.Current edition approved Dec. 1, 2013. Published January 2014. DOI: 10.1520/C1789-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document S
15、ummary page onthe ASTM website.3Available from American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA30329, http:/www.ashrae.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
16、 United States1categorized 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, generally between 1 and 10 MHz.Adm
17、ittancemeters 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 gravity) of the specimen material.3
18、.1.6 equilibrium moisture content, EMCthe 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 chamber that is in thermodynamicequ
19、ilibrium with a sample of material in that chamber.3.1.8 humidity ratio, Wthe ratio of the mass of watervapor to the mass of dry air contained in a sample of moist air.3.1.9 moisture content, MCthe ratio of the mass of waterin a material to the oven-dry mass of the sample expressed asa decimal fract
20、ion 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, the ratio of the amount of watervapor in air to t
21、he amount of water vapor in saturated air at thesame 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 uncertainty ratio, TURcomparison between theaccura
22、cy of the Unit Under Test (UUT) and the estimatedcalibration uncertainty stated with a confidence level of 95%(K=2).3.1.12 water activity, Awthe ratio of the water vaporpressure in a material to the vapor pressure of pure water at thesame temperature.3.1.12.1 DiscussionWater activity is an intrinsic
23、 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 material that is available to impact the perfo
24、rmancecharacteristics 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 measurement ofmoisture content during storage,
25、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 Awwhich is a measure of the amount of moisture in a
26、 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 applications, a separatecalibration is required for ea
27、ch 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 calibrationcurve.4.5.3 Saturate the samples with
28、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 and Use5.1 This Standard Test Method is intend
29、ed for use incalibrating hand-held meters to accurately read from approxi-mately 30% to 90% ERH. Moisture content is related to theERH or water activity of a material.5.2 Hand-held meters provide a rapid means of sampling themoisture content of gypsum boards and panels during manu-facture and for fi
30、eld 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 measurements are influencedby the actual moisture con
31、tent, 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 output andcorrection of readings as specified by
32、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 ranges forprecision and bias as specified in thi
33、s 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 ofmaintaining a steady-state temperature of 45 6 3C
34、(1136 5F).6.1.2 Environmental ChamberChamber capable of main-taining a controlled temperature of 20 6 2C(686 4 F) andrelative humidity within the range 30% to 90% 6 5%.C1789 1326.1.3 Electronic Balance or ScaleElectronic scale capableof weighing each test specimen to within 6 0.10 g (6 0.0035oz).6.1
35、.4 Relative Humidity Test MeterThe meter shall becapable of reading between 30% and 90% relative humidity.The calibrated test uncertainty ratio (TUR) of this meter shallnot be less than 4:1 over the range of measure cited.6.1.4.1 Meter shall have removable temperature/humidityprobes that can be seal
36、ed 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 atmosphere within thebox saturated with water vapor. Ope
37、n 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 Psychrometric ChartGraphical presentation of thether
38、modynamic 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 of 30% to 90%.NOTE 130% relative humidity represents
39、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. Material of the type to be calibrated shall be prepared and
40、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 measuring 100mm wide by 200 mm long (4 in. by 8 in.), for each givensample of board or panel.7.3.1 The specimens shall be di
41、vided into a minimum ofthree (3) groups of 15 specimens each.7.3.2 Each specimen shall be assigned a group designationand a specimen number (e.g., A-1, A-2, A-3, B-1, B-2, B-3,etc.) and labeled with a pencil or waterproof ink.8. Determine Dry Specimen Weights and EquilibriumHumidity Ratios8.1 Determ
42、ine the dry weight of each specimen.8.1.1 Place the test specimens into forced air oven set at 45C (113 F).Arrange the specimens so that heated air circulatesfreely around all sides of the specimens. Use racks or holdersto keep the specimens separated sufficiently to allow air flowbetween the specim
43、ens.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 within 60.10 percent of the dried sample weight.8.1.4 Record the dry weight of each specimen.8.2 Determine the humidity ratio of the
44、 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 content. Humidity ratio and dew-pointtemperature do not vary wi
45、th 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.8.2.2 Insert a temperature/relative humidity probe throughth
46、e 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 intervals.8.2.3.1 Calculate the humidity ratio using a p
47、sychrometricchart 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
48、 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% relative humidity at 20 C (68 F).9.2 Place specimens in a water vapor saturated atmospherein an environmental cha
49、mber or humidity cabinet with relativehumidity equal to or greater than 95% at 20C (68F).9.2.1 Document the environmental chamber conditions us-ing a calibrated relative humidity sensor.9.3 Maintain specimens in the water saturated atmosphereuntil they reach moisture equilibrium with the atmosphere.9.3.1 Maintain specimens in chamber or cabinet until rela-tive humidity stabilizes at a reading of 95% or greater.9.3.2 Remove each specimen and weigh at eight (8) hourintervals.9.3.2.1 Determine the weight of water in the specimen bysubtractin
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