1、Designation: E 408 71 (Reapproved 2002)Standard Test Methods forTotal Normal Emittance of Surfaces Using Inspection-MeterTechniques1This standard is issued under the fixed designation E 408; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, 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 These test methods cover determination of the totalnormal emittance (Note) of surfaces by means o
3、f portable,inspection-meter instruments.NOTE 1Total normal emittance (eN) is defined as the ratio of thenormal radiance of a specimen to that of a blackbody radiator at the sametemperature. The equation relating eNto wavelength and spectral normalemittance eN(l) iseN5 *0Lbl,T!eNl!dl/*0Lbl, T!dl (1)w
4、here:Lb(l,T) = Plancks blackbody radiation function= c1p1l5(ec2/lT1)1,c1= 3.7415 3 1016 Wm2,c2= 1.4388 3 102mK,T = absolute temperature, K,l = wavelength, m,*0Lb(l,T)dl = Dp1T4, andD = Stefan-Boltzmann constant =5.66961 3 108Wm2K41.2 These test methods are intended for measurements onlarge surfaces
5、when rapid measurements must be made andwhere a nondestructive test is desired. They are particularlyuseful for production control tests.1.3 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 e
6、stablish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Summary of Test Methods2.1 At least two different types of instruments are commer-cially available for performing this measurement. One typemeasures radiant energy reflected f
7、rom the specimen (TestMethod A),2and the other type measures radiant energyemitted from the specimen (Test Method B).3A brief descrip-tion of the principles of operation of each test method follows.2.1.1 Test Method AThe theory employed in Test MethodA has been described in detail by Nelson et al4an
8、d therefore isonly briefly reviewed herein. The surface to be measured isplaced against an opening (or aperture) on the portable sensingcomponent. Inside the sensing component are two semi-cylindrical cavities that are maintained at different tempera-tures, one at near ambient and the other at a sli
9、ghtly elevatedtemperature. A suitable drive mechanism is employed to rotatethe cavities alternately across the aperture. As the cavitiesrotate past the specimen aperture, the specimen is alternatelyirradiated with infrared radiation from the two cavities. Thecavity radiation reflected from the speci
10、men is detected with avacuum thermocouple. The vacuum thermocouple views thespecimen at near normal incidence through an optical systemthat transmits radiation through slits in the ends of the cavities.The thermocouple receives both radiation emitted from thespecimen and other surfaces, and cavity r
11、adiation which isreflected from the specimen. Only the reflected energy varieswith this alternate irradiation by the two rotating cavities, andthe detection-amplifying system is made to respond only to thealternating signal. This is accomplished by rotating the cavitiesat the frequency to which the
12、amplifier is tuned. Rectifyingcontacts coupled to this rotation convert the amplifier output toa d-c signal, and this signal is read with a millivoltmeter. Themeter reading must be suitably calibrated with known reflec-tance standards to obtain reflectance values on the test surface.The resulting da
13、ta can be converted to total normal emittanceby subtracting the measured reflectance from unity.2.1.2 Test Method BThe theory of operation of TestMethod B has been described in detail by Gaumer et al5and isbriefly reviewed as follows: The surface to be measured isplaced against the aperture on the p
14、ortable sensing component.Radiant energy which is emitted and reflected from thespecimen passes through a suitable transmitting vacuum win-dow and illuminates a thermopile. The amount of energy1These test methods are under the jurisdiction of ASTM Committee E21 onSpace Simulation and Applications of
15、 Space Technology and are the directresponsibility of Subcommittee E21.04 on Space Simulation Test Methods.Current edition approved May 19, 1971. Published July 1971.2A satisfactory instrument for this type of measurement is the InfraredReflectometer Model DB 100, manufactured by Gier-Dunkle Instrum
16、ents, Inc.,Torrance, CA.3A satisfactory instrument for this type of measurement is the Model 25AEmissometer, manufactured by the Lion Research Corp., Cambridge, MA.4Nelson, K. E., Leudke, E. E., and Bevans, J. T., Journal of Spacecraft andRockets, Vol 3, No. 5, 1966, p. 758.5Gaumer, R. E., Hohnstrei
17、ter, G. F., and Vanderschmidt, G. F., “Measurement ofThermal Radiation Properties of Solids,” NASA SP-31, 1963, p. 117.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.reflected from the specimen is minimized by cooling thethermopile
18、and the cavity walls which the specimen views. Theoutput of the thermopile is amplified and sensed by a suitablemeter. The meter reading must be calibrated with standards ofknown emittance.3. Limitations3.1 Both test methods are limited in accuracy by the degreeto which the emittance properties of c
19、alibrating standards areknown and by the angular emittance characteristics of thesurfaces being measured.3.2 Test Method A is normally subject to a small errorcaused by the difference in wavelength distributions betweenthe radiant energy emitted by the two cavities at differenttemperatures, and that
20、 emitted by a blackbody at the specimentemperature. Test Method B also has nongray errors since thedetector is not at absolute zero temperature. The magnitude ofthis type of error is discussed by Nelson et al.43.3 Test Method A is subject to small errors that may beintroduced if the orientation of t
21、he sensing component ischanged between calibration and specimen measurements.This type of error results from minor changes in alignment ofthe optical system.3.4 Test Method A is subject to error when curved specularsurfaces of less than about 300-mm radius are measured. Theseerrors can be minimized
22、by using calibrating standards thathave the same radius of curvature as the test surface.3.5 Test Method A can measure reflectance on specimensthat are either opaque or semi-transparent in the wavelengthregion of interest (about 4 to 50 m). However, if emittance isto be derived from the reflectance
23、data on a semi-transparentspecimen, a correction must be made for transmittance losses.3.6 Test Method B is subject to several possible significanterrors. These may be due to (1) variation of the test surfacetemperature during measurements, (2) differences in tempera-ture between the calibrating sta
24、ndards and the test surfaces, (3)changes in orientation of the sensing component betweencalibration and measurement, (4) errors due to irradiation ofthe specimen with thermal radiation by the sensing component,and (5) errors due to specimen curvature. Variations in testsurface temperature severely l
25、imit accuracy when specimensthat are thin or have low thermal conductivity are beingmeasured. Great care must be taken to maintain the sametemperature on the test surface and calibrating standards. Meterreadings are directly proportional to the radiant flux emitted bythe test surface, which in turn
26、is proportional to the fourthpower of temperature. Changes in orientation of the sensingcomponent between calibration and test measurement intro-duces errors due to temperature changes of the thermopile. Therelatively poor vaccuum around the thermopile results invariations in convection heat transfe
27、r coefficients which areaffected by orientation.3.7 Test Method B is limited to emittance measurements onspecimens that are opaque to infrared radiation in the wave-length region of interest (about 4 to 50 m).3.8 The emittance measured by Test Method B is anintermediate value between total-normal an
28、d total-hemispherical emittance because of the relationship betweenthe thermocouple sensing elements and the test surface. Theclose proximity of the thermopile to the relatively large testsurface allows it to receive radiation emitted over a significantangle (up to 80). This error (the difference be
29、tween total-normal and total-hemispherical) emittance can be as large as10 % on certain types of specimens (such as specular metalsurfaces).4. Procedure4.1 Calibration procedures for both test methods of mea-surement are jointly discussed because of their similarity. InTest Method A infrared reflect
30、ance properties of calibratingstandards must be known, and for Test Method B emittancevalues of standards are utilized. Following an appropriatewarm-up time, calibrate the readout meter. Adjust the meter togive the correct reading when measuring both high and lowemittance (or reflectance) standards.
31、 Repeat calibration of themeter several times at short time intervals until the correctreadings can be obtained near each end of the scale. Typicalhigh and low emittance (low and high reflectance) standardsmay consist of black paint (or preferably a blackbody cavity)and polished high-purity aluminum
32、, respectively. Measure thethermal radiation properties of the standards independentlywith an absolute instrument, and maintain the standards in aclean condition thereafter.4.2 In Test Method B care must be taken to prevent strayradiant energy from entering the sensor. This can occur if thetest surf
33、ace is not sufficiently flat or is not opaque.4.3 In Test Method B the test surfaces and calibratingstandards must be maintained at the same temperature. If thin(less than about 0.7 mm thick) conducting specimens are to bemeasured, they should be bonded to a thick metallic substrate.Specimen tempera
34、ture changes can be noted by observingwhether the indicated meter reading drifts with time.4.4 In Test Method B the orientation of the sensor must bethe same for both calibration and test surface measurements.4.5 After the meter has been properly calibrated, place thetest surface over the aperture o
35、f the measuring instrument. Theresulting meter reading of Test Method A is then the infraredreflectance for blackbody radiant energy at near room tempera-ture, or in Test Method B, a meter reading that can beconverted to emittance using the manufacturers emittance/meter reading conversion data. In T
36、est Method A, obtain theemittance by subtracting the reflectance from unity. It isrecommended that the instrument be recalibrated as soon aspossible after measuring the test surface. If the meter calibra-tion has changed, repeat the entire calibration and readoutprocedure. It is recommended that at
37、least three readings betaken for each test specimen, and the results averaged, tominimize statistical errors. It is also recommended that bothlaboratory and working emittance (or reflectance) standards bemaintained, and that they be kept clean.5. Report5.1 Report the following information:5.1.1 Name
38、 and pertinent other identification of the testmaterial,5.1.2 Name and pertinent other identification or traceabilityof the surfaces used for calibration,E 40825.1.3 Emittance (or reflectance) values assumed for calibra-tion surfaces,5.1.4 Locations on the surface area at which emittance (orreflecta
39、nce) measurements were performed (not applicable forsmall individual test specimens),5.1.5 Ambient temperature,5.1.6 For Test Method A the indicated meter reading (re-flectance) shall be recorded for three successive measurements.An average of the three values shall than be calculated andsubtracted
40、from one to obtain the emittance,5.1.7 For Test Method B the indicated meter reading shallbe recorded for three successive measurements. These meterreadings shall be converted to emittance using the manufac-turers data, and then averaged, and5.1.8 Date and time the measurements were taken.6. Keyword
41、s6.1 emittance; infrared emittance; material radiative prop-erty; normal emittance; radiative heat transfer; spacecraftthermal control; thermal radiationASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. U
42、sers of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed eve
43、ry five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible techn
44、ical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E 4083
