1、Designation: C1789 14Standard 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 year of last revis
2、ion. 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 fiber-rein
3、forced 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 the dry
4、ing 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 use. It is therespon
5、sibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C473 Test Methods for Physical Testing of Gypsum PanelProductsC1177 Specification for Glass M
6、at Gypsum Substrate forUse as SheathingC1178 Specification for Coated Glass Mat Water-ResistantGypsum Backing PanelC1278 Specification for Fiber-Reinforced Gypsum PanelC1396 Specification for Gypsum BoardD4442 Test Methods for Direct Moisture Content Measure-ment of Wood and Wood-Base MaterialsD4444
7、 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 and Air-conditioning Engineers3. Terminology3.1 Definitions of Terms Specific to This S
8、tandard: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 through a material.3.1.3 conductance meters, nconductance meters are thosethat measure pre
9、dominantly 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 are commonly referred to as“resistance“ meters. Most commercial conductance meters areh
10、igh-input impedance (about 1012), wide-range (104to 1012) ohmmeters. Their scales are generally calibrated to readdirectly in moisture content (oven-dry mass basis) for aparticular calibration material and at a specific referencetemperature.3.1.4 dew-point temperature, td,nthe temperature atwhich a
11、sample of moist air being cooled at constant pressureand moisture content reaches 100 percent relative humidity.3.1.4.1 DiscussionThe dew-point temperature is the tem-perature at which water condensation begins to occur on acooled surface in contact with moist air.3.1.5 dielectric meters, nmeters th
12、at measure primarily byadmittance or power loss.3.1.5.1 DiscussionDielectric meters generally do not havepins that penetrate into the material being measured. There aretwo general types of dielectric meters that may be arbitrarilycategorized by their predominant mode of response admit-tance (or capa
13、citance) and power loss. Both have surfacecontact electrodes and readout scales that are usually marked in1This 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
14、Test Methods for Gypsum Products.Current edition approved June 1, 2014. Published July 2014. Originally approvedin 2013. Last previous edition approved in 2013 as C1789 13. DOI: 10.1520/C1789-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at
15、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, GA30329, http:/www.ashrae.
16、org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1arbitrary units. Most dielectric meters operate in the r-ffrequency range, generally between 1 and 10 MHz.Admittancemeters respond primarily to the capacitance (dielectric con-stant)
17、 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.3.1.6 equilibrium moisture content, EMC, nthe moisturecontent of a materia
18、l 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 thermodynamicequilibrium with a sample of material in that chamber.3.1.8 humidity rati
19、o, 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 the sampleexpressed as a decimal fraction or percentage.3.1.9.1 DiscussionOven-dry refers to the remov
20、al 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 ratio of the amount ofwater vapor in air to the amount of water vapor in saturated airat the same temperatu
21、re 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, TUR, ncomparison betweenthe accuracy of the Unit Under Test (UUT) and the estimatedcalibratio
22、n 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.3.1.12.1 DiscussionWater activity is an intrinsic propertyderived from fundamental principles of thermody
23、namics 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 performancecharacteristics of the material or to support mold
24、 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, construction and use inbuilding assemblies.4.2 The calib
25、ration 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 material thatis available to impact the performance cha
26、racteristics 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 each type of gypsum board or panelto be measured.4.5 The t
27、est 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 water.4.5.4 Dry the samples in steps, recording after ea
28、ch 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 intended for use incalibrating hand-held meters to accurately
29、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 boards and panels during manu-facture and for field inspection during and after buildingconstruction. How
30、ever, 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 content, a number of other gypsumboard and panel variables,
31、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 these test methods.5.3 Electrical conductance and dielect
32、ric 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 this standard.5.4 Both types of meters are to be calibrated
33、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 (113 65F).6.1.2 Environmental ChamberChamber capable of
34、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 each test specimen to within 60.10 g (60.0035oz).6.1.4 Relative Humidity Test MeterThe meter shall becapable of readin
35、g between 30 and 90 % relative humidity. TheC1789 142calibrated 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 removable temperature/humidityprobes that can be sealed into sealed plastic bags.6.1.5 Humidity BoxInsulated b
36、ox 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. Open mesh shelving or racksare used to support samples above
37、 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 thethermodynamic properties of moist air.7. Laboratory Calibrati
38、on7.1 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 a practical lower limit onmoisture content found in build
39、ings 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 tested ina manner that is consistent with the following c
40、alibration 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 divided into a minimum ofthree (3) groups of 15 specimens e
41、ach.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, etc.) and labeled with a pencil or waterproof ink.8. Determine Dry Specimen Weights and EquilibriumHumidity Ratios8.1 Determine the dry weight of each specimen.8.1.1 Place the
42、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 specimens.8.1.2 Remove and weigh each test specimen at one
43、 hourintervals.8.1.3 The test specimen is deemed to be dry when threeconsecutive weighings show no change in weight within 60.10percent of the dried sample weight.8.1.4 Record the dry weight of each specimen.8.2 Determine the humidity ratio of the trapped environ-ment that is in moisture equilibrium
44、 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 with temperature at constant moisture content andcan be
45、 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 throughthe wall of the bag and seal tightly.NOTE 3Making a sma
46、ll 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 psychrometricchart or a table of thermodynamic propert
47、ies 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%(A
48、wof 0.8) the test specimens must be saturated abovethis point as a starting point for calibration. The targetsaturation level is 95 % relative humidity at 20C (68F).9.2 Place specimens in a water vapor saturated atmospherein an environmental chamber or humidity cabinet with relativehumidity equal to
49、 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 bysubtracting the dry weight of the sample as determinedaccordi
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