1、Designation: E337 15Standard Test Method forMeasuring Humidity with a Psychrometer (the Measurementof Wet- and Dry-Bulb Temperatures)1This standard is issued under the fixed designation E337; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, the 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 General:1.1.1 This test method covers the determination of thehumidity of atmospheric air by mean
3、s of wet- and dry-bulbtemperature readings.1.1.2 This test method is applicable for meteorologicalmeasurements at the earths surface, for the purpose of thetesting of materials, and for the determination of the relativehumidity of most standard atmospheres and test atmospheres.1.1.3 This test method
4、 is also applicable when the tempera-ture of the wet bulb only is required. In this case, theinstrument comprises a wet-bulb thermometer only.1.1.4 Relative humidity (RH) does not denote a unit. Un-certainties in the relative humidity are expressed in the formRH 6 rh %, which means that the relative
5、 humidity is expectedto lie in the range (RH rh) % to (RH + rh ) %, where RH isthe observed relative humidity.All uncertainties are at the 95 %confidence level.1.2 Method APsychrometer Ventilated by Aspiration:1.2.1 This method incorporates the psychrometer ventilatedby aspiration. The aspirated psy
6、chrometer is more accuratethan the sling (whirling) psychrometer (see Method B), and itoffers advantages in regard to the space which it requires, thepossibility of using alternative types of thermometers (forexample, electrical), easier shielding of thermometer bulbsfrom extraneous radiation, accid
7、ental breakage, and conve-nience.1.2.2 This method is applicable within the ambient tempera-ture range 5 to 80C, wet-bulb temperatures not lower than1C, and restricted to ambient pressures not differing fromstandard atmospheric pressure by more than 30 %.1.3 Method BPsychrometer Ventilated by Whirli
8、ng (SlingPsychrometer):1.3.1 This method incorporates the psychrometer ventilatedby whirling (sling psychrometer).1.3.2 This method is applicable within the ambient tempera-ture range 5 to 50C, wet-bulb temperatures not lower than 1Cand restricted to ambient pressures not differing from standardatmo
9、spheric pressure by more than 30 %.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 WarningMercury has been designated by many regu-latory agencies as a hazardous material that can cause seriousmedical issues. Mercury, or
10、 its vapor, has been demonstrated tobe hazardous to health and corrosive to materials. Cautionshould be taken when handling mercury and mercury contain-ing products. See the applicable product Safety Data Sheet(SDS) for additional information. Users should be aware thatselling mercury and/or mercury
11、 containing products into yourstate or country may be prohibited by law.1.6 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 t
12、he applica-bility of regulatory limitations prior to use. (For more specificsafety precautionary statements, see 8.1 and 15.1.)2. Referenced Documents2.1 ASTM Standards:2D861 Practice for Use of theTex System to Designate LinearDensity of Fibers, Yarn Intermediates, and YarnsD1193 Specification for
13、Reagent WaterD1356 Terminology Relating to Sampling and Analysis ofAtmospheresD1357 Practice for Planning the Sampling of the AmbientAtmosphereD3631 Test Methods for Measuring Surface AtmosphericPressureD4023 Terminology Relating to Humidity Measurements(Withdrawn 2002)31This test method is under th
14、e jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.11 on Meteorology.Current edition approved July 1, 2015. Published July 2015. Originally approvedin 1931. Last previous edition approved in 2007 as E337 02 (2007). DOI:10.1520/E0337-15.2For refere
15、nced 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 Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onw
16、ww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1D4230 Test Method of Measuring Humidity with Cooled-Surface Condensation (Dew-Point) HygrometerE1 Specification for ASTM Liquid-in-Glass ThermometersE2251 Specification for L
17、iquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision LiquidsIEEE/ASTM SI-10 Practice for Use of the InternationalSystem of Units (SI) (the Modernized Metric System)3. Terminology3.1 Definitions:3.1.1 For definitions of humidity terms used in this testmethod, refer to Terminology D4023.3.1.2 F
18、or definitions of other terms in this test method, referto Terminology D1356.3.2 Definitions of Terms Specific to This Standard:3.2.1 Method AAspirated Psychrometer:3.2.1.1 aspirationthe wet and dry bulbs (and the psy-chrometer) are described as aspirated because there is provi-sion for the forced v
19、entilation by drawing air over the bulbs bysuction. The flow may be either transverse or parallel to theaxes of the bulbs.3.2.1.2 thermometerfor purposes of this standard, andexcept where a specific type is indicated, the term thermometermeans any temperature-measuring device.3.2.1.3 wet-bulb coveri
20、ng and wickthe wet bulb is pro-vided with a water-retaining covering of a woven-cottonmaterial.Acotton wick which connects the covering to a waterreservoir may be provided so that water is fed to the coveringcontinuously by capillarity.3.2.2 Method BSling Psychrometer:3.2.2.1 ventilationthe wet and
21、dry bulbs (and the psy-chrometer) are described as ventilated because there is provi-sion for a flow of the air over the bulbs. The flow is transverseto the axes of the bulbs.3.2.2.2 wet-bulb coveringthe wet bulb is provided with awater-retaining covering of a woven-cotton material.4. Summary of Met
22、hods4.1 General:4.1.1 The wet-bulb temperature depression, the dry-bulbtemperature, and the ambient pressure provide the basis forderiving the relative humidity.4.2 Method AAspirated Psychrometer:4.2.1 Establish the airflow (see 7.4) and maintain it until aminimum wet-bulb temperature is attained. (
23、With mercury-in-glass thermometers, about 2-min ventilation time is usuallynecessary.)4.2.2 Read the thermometers with the necessary precision,obtaining the dry-bulb temperature with an overall uncertaintyof 60.2C or better, and the temperature depression with anoverall uncertainty of 60.2C or bette
24、r for an uncertainty in therelative humidity of 63 % RH. For an uncertainty in therelative humidity of 62 % RH, obtain the dry-bulb temperaturewith an overall uncertainty of 60.2C or better and thetemperature depression with an overall uncertainty of 60.1Cor better. (Also see Section 12.)4.3 Method
25、BSling Psychrometer:4.3.1 Holding the instrument well away from the body, andfor outdoor measurements to windward and in the shade, whirlit at such a rate as to achieve the specified airspeed at the wetand dry bulbs, see 14.4.4.3.2 Read the thermometers with the necessary precision,obtaining the dry
26、-bulb temperature with an overall uncertaintyof 60.6C or better, and the temperature depression with anoverall uncertainty of 60.3C or better for an uncertainty in therelative humidity of 65 % RH, also see Section 19.5. Significance and Use5.1 The object of this test method is to provide guidelinesf
27、or the construction of a psychrometer and the techniquesrequired for accurately measuring the humidity in the atmo-sphere. Only the essential features of the psychrometer arespecified.METHOD APSYCHROMETER VENTILATEDBY ASPIRATION6. Interferences6.1 When an aspirated psychrometer is used for measure-m
28、ents in a small enclosed space and steadily rising wet- anddry-bulb temperatures are observed, consider whether heat andmoisture liberated by the instrument itself are affecting theconditions.6.2 While the thermometers are being read, keep all surfacesthat are at temperatures other than the environm
29、ent (such as thehands, face, and other warmer or colder objects) as far aspossible from the thermometer bulbs.6.3 This method should not be used where there is heavycontamination of the air with gases, vapors, or dust.7. Apparatus7.1 Thermometers for an Aspirated Psychrometer:7.1.1 The range of the
30、thermometers shall not exceed therange 0 to 80C. This range may be achieved by providingmore than a single pair of matched thermometers. When theuncertainty in the derived relative humidity is required to benot more than 63 % RH, the thermometers shall be such thattheir readings give the temperature
31、 depression with an uncer-tainty of not more than 60.2C. When the uncertainty in therelative humidity is required to be not more than 62 % RH,they shall be such that their readings give the temperaturedepression with an uncertainty of not more than 60.1C. Theuncertainty in the reading of the dry-bul
32、b temperature shall benot more than 60.2C.7.1.2 Electrical thermometers may be so connected that thereadings give the temperature depression and the dry-bulbtemperature directly.7.1.3 Each thermometer shall consist of a temperaturesensor of essentially cylindrical shape which is supported on asingle
33、 stem, the stem being coaxial with the sensor. The freeend of each sensor shall be smoothly rounded. If the diameterof the stems is small, compared with that of the sensors, thenboth ends of each sensor shall be smoothly rounded.The sensorE337 152of a thermometer shall be that part of the thermomete
34、rextending from the bottom of the bulb to the top of the entranceflare of the capillary.7.1.4 With transverse ventilation, the diameters of the sen-sors (excluding wet covering) shall be not less than 1 mm andnot greater than 4 mm.7.1.5 With axial ventilation, the diameters of the sensors(excluding
35、wet covering) shall be not less than 2 mm and notgreater than 5 mm, and their length not less than 10 mm andnot greater than 30 mm.7.1.6 The connecting wires of electrical thermometers shallbe contained within the supporting stems and shall be isolatedfrom the moisture of the wet covering.7.1.7 Ther
36、mometers shall be graduated to 0.5C or closerand be capable of being read to the nearest 0.1C or better. (Aspecification for mercury-in-glass thermometers suitable whenthe uncertainty in the derived relative humidity is required tobe not more than 63 % RH is given in Annex A1.)7.2 Wet-Bulb Covering,
37、 Wick, and Water Reservoir:7.2.1 The covering shall be fabricated from white-cottonmuslin of linear density from 1.0 to 1.2 g/m, refer to PracticeD861. A seamless sleeve is preferred, but a seam ispermissible, provided that it does not add appreciably to thegeneral roughness which the weave imparts
38、to the surface.7.2.2 The covering shall completely cover the sensor orbulb of the thermometer, fit snugly but not very tightly, andshall be in physical contact with the bulb over its entire surface.It shall extend onto the stem for such a distance that the errorin the observed wet-bulb temperature d
39、ue to heat conductionalong the stem does not exceed 0.05C. (A method of deter-mining the distance for which the covering must extend ontothe stem is outlined in Annex A2. For mercury-in-glassthermometers with solid stems, a distance of twice the stemdiameter is usually adequate.)7.2.3 To maintain a
40、snugly fit cover on the wet bulb, thecovering may be secured with a cotton thread at the end of thecovering on the stem of the thermometer, at the top of thethermometer bulb, and at the bottom of the bulb. However,whenever a wicking is used, the covering shall not be securedbetween the thermometer b
41、ulb and the cotton wicking whichconnects the covering to a water reservoir.7.2.4 After fabrication, the covering and wick shall havebeen washed in a dilute solution of sodium carbonate andthoroughly rinsed with distilled water. They shall not subse-quently be touched with the fingers.7.2.5 The stem
42、of each thermometer shall, for a lengthmeasured from the sensor and not less than 1.5 the length ofthe extension of the covering required by 7.2.2, be clear ofobstructions and freely exposed to the airstream.7.2.6 During the test, the covering shall be completelypermeated with water as evidenced by
43、a glistening appearancein a beam of light.7.2.7 The covering shall be washed in situ with distilledwater from time to time and be renewed when it shows anyevidence of permanent change.7.2.8 When a wick is provided, the free length of a wickshall be at least twice the diameter of the wet bulb and at
44、leastthree times the wick diameter, ensuring that water arriving atthe covering is already at practically the wet-bulb temperature.A wick shall be limp.7.2.9 Awater reservoir shall not obstruct the airflow, and itscontents shall not affect the humidity of the sample air.7.2.10 The level of the water
45、 in a water reservoir shall bebetween 5 and 25 mm below the level of the lowest part of thewet bulb.7.3 WaterReagent water shall be produced by distillation,or by ion exchange or reverse osmosis followed by distillation,refer to Specification D1193.7.4 Airflow:7.4.1 The flow of air over both the wet
46、 and dry bulbs shallbe a forced draught of 3 to 10 m/s for thermometers withmaximum allowable diameter of the sensors.7.4.2 The sample air shall not pass over any obstruction orthrough a fan before it passes over the wet and dry bulbs.7.4.3 With axial flow, the direction of the flow shall be fromthe
47、 free end of each sensor towards the support end.7.4.4 No air which has been cooled by the wet bulb or by thewick shall impinge on the dry bulb.7.5 Radiation Shields:7.5.1 Any radiation shields shall be of metal with a thick-ness of 0.4 to 0.8 mm. Surfaces required to have a polishedfinish shall be
48、of a bare metal which will retain its brightness.7.5.2 With transverse ventilation, radiation shields may beprovided to shield the wet and dry bulbs from extraneousradiations. The radiation shields, essentially in the form ofparallel plates, can be either polished on the outside andblackened on the
49、inside, or polished on both the inside andoutside surfaces. The clearance between the wet and dry bulbsand the shields shall be not less than half the overall diameterof the wet bulb. The shields shall be liberally flared outwardsat the inlet to prevent the flow separating from the shields onthe inside (vena-contracta effect). The shields may form part ofa duct for the airflow.Asecond shield, outside, is not necessary.7.5.3 With axial ventilation, concentric radiation shieldsshall be provided for the wet and dry bulbs, and shall bepolished inside a
