1、Designation: E 337 02 (Reapproved 2007)Standard Test Method forMeasuring Humidity with a Psychrometer (the Measurementof Wet- and Dry-Bulb Temperatures)1This standard is issued under the fixed designation E 337; the number immediately following the designation indicates the year oforiginal adoption
2、or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 at
3、mospheric air by means 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
4、.1.3 This test method 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 me
5、ans that the relative 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 aspirati
6、on. The aspirated psychrometer 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 extran
7、eous radiation, accidental 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
8、 Ventilated by Whirling (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 differ
9、ing from standardatmospheric pressure by more than 30 %.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-bilit
10、y of regulatory limitations prior to use. (For more specificsafety precautionary statements, see 8.1 and 15.1.)2. Referenced Documents2.1 ASTM Standards:2D 861 Practice for Use of the Tex System to DesignateLinear Density of Fibers, Yarn Intermediates, and YarnsD 1193 Specification for Reagent Water
11、D 1356 Terminology Relating to Sampling and Analysis ofAtmospheresD 1357 Practice for Planning the Sampling of the AmbientAtmosphereD 3631 Test Methods for Measuring Surface AtmosphericPressureD 4023 Terminology Relating to Humidity Measurements3D 4230 Test Method of Measuring Humidity with Cooled-S
12、urface Condensation (Dew-Point) HygrometerE1 Specification for ASTM Liquid-in-Glass ThermometersIEEE/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
13、 to Terminology D 4023.3.1.2 For definitions of other terms in this test method, referto Terminology D 1356.1This test method is under the jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.11 on Meteorology.Current edition approved Oct. 1, 2007. Pu
14、blished December 2007. Originallyapproved in 1931. Last previous edition approved in 2002 as E337 - 02.2For 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
15、 Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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
16、 the psy-chrometer) are described as aspirated because there is provi-sion for the forced ventilation 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 in
17、dicated, the term thermometermeans any temperature-measuring device.3.2.1.3 wet-bulb covering 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 coveringc
18、ontinuously by capillarity.3.2.2 Method BSling Psychrometer:3.2.2.1 ventilationthe wet and 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 b
19、ulb is provided with awater-retaining covering of a woven-cotton material.4. Summary of Methods4.1 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 Establi
20、sh the airflow (see 7.4) and maintain it until aminimum wet-bulb temperature is attained. (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 6
21、0.2C or better, and the temperature depression with anoverall uncertainty of 60.2C or better 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
22、depression with an overall uncertainty of 60.1Cor better. (Also see Section 12.)4.3 Method 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
23、 bulbs, see 14.4.4.3.2 Read the thermometers with the necessary precision,obtaining the dry-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 Sec
24、tion 19.5. Significance and Use5.1 The object of this test method is to provide guidelinesfor 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 VENT
25、ILATEDBY ASPIRATION6. Interferences6.1 When an aspirated psychrometer is used for measure-ments 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 the
26、rmometers are being read, keep all surfacesthat are at temperatures other than the environment (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,
27、 or dust.7. Apparatus7.1 Thermometers for an Aspirated Psychrometer:7.1.1 The range of the 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 beno
28、t more than 63 % RH, the thermometers shall be such thattheir readings give the temperature 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 temperaturedepressi
29、on with an uncertainty of not more than 60.1C. Theuncertainty in the reading of the dry-bulb 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 co
30、nsist of a temperaturesensor of essentially cylindrical shape which is supported on asingle 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
31、be smoothly rounded.The sensorof a mercury-in-glass thermometer shall be that part of thethermometer extending from the bottom of the bulb to the topof the entrance flare of the capillary.7.1.4 With transverse ventilation, the diameters of the sen-sors (excluding wet covering) shall be not less than
32、 1 mm andnot greater than 4 mm.7.1.5 With axial ventilation, the diameters of the sensors(excluding 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 contain
33、ed within the supporting stems and shall be isolatedfrom the moisture of the wet covering.7.1.7 Mercury-in-glass 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 deriv
34、ed relative humidity is required tobe not more than 63 % RH is given in Annex A1.)7.2 Wet-Bulb Covering, Wick, and Water Reservoir:E 337 02 (2007)27.2.1 The covering shall be fabricated from white-cottonmuslin of linear density from 1.0 to 1.2 g/m, refer to PracticeD 861. A seamless sleeve is prefer
35、red, but a seam is permis-sible, provided that it does not add appreciably to the generalroughness which the weave imparts 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 ove
36、r its entire surface.It shall extend onto the stem for such a distance that the errorin the observed wet-bulb temperature due 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 me
37、rcury-in-glassthermometers with solid stems, a distance of twice the stemdiameter is usually adequate.)7.2.3 To maintain a 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, an
38、d at the bottom of the bulb. However,whenever a wicking is used, the covering shall not be securedbetween the thermometer bulb 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 ca
39、rbonate andthoroughly rinsed with distilled water. They shall not subse-quently be touched with the fingers.7.2.5 The stem of each thermometer shall, for a lengthmeasured from the sensor and not less than 1.53 the length ofthe extension of the covering required by 7.2.2, be clear ofobstructions and
40、freely exposed to the airstream.7.2.6 During the test, the covering shall be completelypermeated with water as evidenced by 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
41、 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 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 s
42、hall not obstruct the airflow, and itscontents shall not affect the humidity of the sample air.7.2.10 The level of the water 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
43、or reverse osmosis followed by distillation,refer to Specification D 1193.7.4 Airflow:7.4.1 The flow of air over both the wet 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
44、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 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
45、 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 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.
46、 The radiation shields, essentially in the form ofparallel plates, can be either polished on the outside andblackened on the 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 w
47、et 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 sh
48、ieldsshall be provided for the wet and dry bulbs, and shall bepolished inside and out. (The shield around the wet bulb playsa vital role in reducing the radiative heat transfer between thatbulb and its surroundings by a factor of about three.) Thediameter of the shield shall be not less than 1.8 d a
49、nd notgreater than 2.5 d, where d is the overall diameter of the wetbulb. Its length and position shall be such that its projectionbeyond each end of the wet covering is not less than d and notgreater than 3 d. The entrance to the shield shall be liberallyflared to form a bell-mouth to prevent the flow separating fromthe shield on the inside. The shield may serve also as the ductfor the airflow. A second shield, outside, is not necessary.8. Precautions8.1 Safety PrecautionsMercury vapor is poisonous, evenin small quantities, and prolonged exposure can
