1、Designation: E452 02 (Reapproved 2018)Standard Test Method forCalibration of Refractory Metal Thermocouples Using aRadiation Thermometer1This standard is issued under the fixed designation E452; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f revision, 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 This test method covers the calibration of refractorymetal thermocouples using a radiation the
3、rmometer as thestandard instrument. This test method is intended for use withtypes of thermocouples that cannot be exposed to an oxidizingatmosphere. These procedures are appropriate for thermo-couple calibrations at temperatures above 800C (1472F).1.2 The calibration method is applicable to the fol
4、lowingthermocouple assemblies:1.2.1 Type 1Bare-wire thermocouple assemblies in whichvacuum or an inert or reducing gas is the only electricalinsulating medium between the thermoelements.1.2.2 Type 2Assemblies in which loose fitting ceramicinsulating pieces, such as single-bore or double-bore tubes,
5、areplaced over the thermoelements.1.2.3 Type 2AAssemblies in which loose fitting ceramicinsulating pieces, such as single-bore or double-bore tubes, areplaced over the thermoelements, permanently enclosed andsealed in a loose fitting metal or ceramic tube.1.2.4 Type 3Swaged assemblies in which a ref
6、ractoryinsulating powder is compressed around the thermoelementsand encased in a thin-walled tube or sheath made of a highmelting point metal or alloy.1.2.5 Type 4Thermocouple assemblies in which one ther-moelement is in the shape of a closed-end protection tube andthe other thermoelement is a solid
7、 wire or rod that is coaxiallysupported inside the closed-end tube. The space between thetwo thermoelements can be filled with an inert or reducing gas,or with ceramic insulating materials, or kept under vacuum.1.3 This standard does not purport to address all of thesafety concerns, if any, associat
8、ed with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recogn
9、ized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E344 Terminology Relat
10、ing to Thermometry and Hydrom-etryE563 Practice for Preparation and Use of an Ice-Point Bathas a Reference TemperatureE988 Temperature-Electromotive Force (EMF) Tables forTungsten-Rhenium Thermocouples (Withdrawn 2011)3E1256 Test Methods for Radiation Thermometers (SingleWaveband Type)E1751 Guide fo
11、r Temperature Electromotive Force (EMF)Tables for Non-Letter Designated Thermocouple Combi-nations (Withdrawn 2009)33. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method seeTerminology E344.3.1.2 radiation thermometer, nradiometer calibrated toindicate the temperature
12、 of a blackbody.3.1.2.1 DiscussionRadiation thermometers include instru-ments having the following or similar names: (1) opticalradiation thermometer, (2) photoelectric pyrometer, ( 3) singlewavelength automatic thermometer, (4) disappearing filamentpyrometer, (5) dual wavelength pyrometer or ratio
13、radiationthermometer, (6) visual optical thermometer, (7) infraredthermometer, (8) infrared pyrometer, and permutations on theterms above as well as some manufacturer-specific names.3.2 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction of ASTM Committee E20 o
14、nTemperature Measurementand is the direct responsibility of Subcommittee E20.11on Thermocouples - Calibration.Current edition approved April 1, 2018. Published April 2018. Originallyapproved in 1972. Last previous edition approved in 2013 as E452 02 (2013).DOI: 10.1520/E0452-02R18.2For referenced AS
15、TM 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 onwww.astm
16、.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of
17、International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.1 automatic radiation thermometer, nradiation ther-mometer whose temperature reading is determined by elec-tronic means.3.2.2 disappearing filament pyrometer, n
18、radiation ther-mometer that requires an observer to match visually thebrightness of a heated filament mounted inside the radiationthermometer to that of the measured object.3.2.3 equalizing block, nobject, usually metal, that whenplaced in a nonuniform temperature region, has greater tem-perature un
19、iformity (due to its relatively high thermoconduc-tivity and mass) than the medium surrounding the object.3.2.4 spectral emissivity, nratio of the spectral radiance ata point on a particular specimen and in a particular directionfrom that point to that emitted by a blackbody at the sametemperature.3
20、.2.5 spectral radiance, npower radiated by a specimen ina particular direction, per unit wavelength, per unit projectedarea of the specimen, and per unit solid angle.3.2.6 spectral response, nsignal detected by a radiometerat a particular wavelength of incident radiation, per unit powerof incident r
21、adiation.3.2.7 test thermocouple, nthermocouple that is to have itstemperature-emf relationship determined by reference to atemperature standard.3.2.8 thermocouple calibration point, n temperature, es-tablished by a standard, at which the emf developed by athermocouple is determined.4. Summary of Te
22、st Method4.1 The thermocouple is calibrated by determining thetemperature of its measuring junction with a radiation ther-mometer and recording the emf of the thermocouple at thattemperature. The measuring junction of the thermocouple isplaced in an equalizing block containing a cavity whichapproxim
23、ates blackbody conditions. The radiation thermom-eter is sighted on the cavity in the equalizing block and theblackbody temperature or true temperature of the block,including the measuring junction, is determined.4.2 Since the spectral emissivity of the radiation emanatingfrom a properly designed bl
24、ackbody is considered unity (one)for all practical purposes, no spectral emissivity correctionsneed be applied to optical pyrometer determinations of theblackbody temperature.4.3 Although the use of a radiation thermometer (Note 1)isless may require more effort and more complex apparatus toachieve a
25、 sensitivity equivalent to that of commonly usedthermocouples, a radiation thermometer has the advantage ofbeing physically separated from the test assembly; thus, itscalibration is not influenced by the temperatures and atmo-spheres in the test chamber. By comparison, a standardthermocouple that is
26、 used to calibrate another thermocouplemust be subjected to the temperatures at which the calibrationsare performed and in some cases must be exposed to theenvironment that is common to the test thermocouple. If astandard thermocouple is exposed to high temperatures orcontaminating environments, or
27、both, for long periods of time,its calibration becomes questionable and the uncertainty in thebias of the calibration increases.NOTE 1Disappearing filament pyrometers are somewhat less sensitivethan many of the thermocouples used above 800C (1472F). Theadvantages of physical separation of the disapp
28、earing filament pyrometerfrom the test assembly may still justify its use over use of a standardthermocouple.5. Significance and Use5.1 This test method is intended to be used by wireproducers and thermocouple manufacturers for certification ofrefractory metal thermocouples. It is intended to provid
29、e aconsistent method for calibration of refractory metal thermo-couples referenced to a calibrated radiation thermometer.Uncertainty in calibration and operation of the radiationthermometer, and proper construction and use of the testfurnace are of primary importance.5.2 Calibration establishes the
30、temperature-emf relationshipfor a particular thermocouple under a specific temperature andchemical environment. However, during high temperaturecalibration or application at elevated temperatures in vacuum,oxidizing, reducing or contaminating environments, and de-pending on temperature distribution,
31、 local irreversible changesmay occur in the Seebeck Coefficient of one or both thermo-elements. If the introduced inhomogeneities are significant, theemf from the thermocouple will depend on the distribution oftemperature between the measuring and reference junctions.5.3 At high temperatures, the ac
32、curacy of refractory metalthermocouples may be limited by electrical shunting errorsthrough the ceramic insulators of the thermocouple assembly.This effect may be reduced by careful choice of the insulatormaterial, but above approximately 2100C, the electricalshunting errors may be significant even
33、for the best insulatorsavailable.6. Sources of Error6.1 The most prevalent sources of error (Note 2) in thismethod of calibration are: (1) improper design of the black-body enclosure, (2) severe temperature gradients in the vicinityof the blackbody enclosure, ( 3) heat conduction losses alongthe the
34、rmoelements, and (4) improper alignment of the radia-tion thermometer with respect to the blackbody cavity andunaccounted transmission losses along the optical path of theradiation thermometer.NOTE 2These are exclusive of any errors that are made in theradiation thermometer measurements or the therm
35、ocouple-emf measure-ments.7. Apparatus7.1 Furnace:7.1.1 The calibration furnace should be designed so that anytemperature within the desired calibration temperature rangecan be maintained constant within a maximum change of 1C(1.8F) per minute in the equalizing block over the period ofany observatio
36、n. Figs. 1-3 show three types of furnaces (1 andE452 02 (2018)21. Caps for making vacuum tight seals around the thermoelements. A cylinder 18. Furnace shell (brass).type neoprene gasket is compressed around the thermoelements. 19. First radiation shield. 0.020-in. (0.51-mm) tantalum sheet rolled int
37、o a cylinder2. Kovar metal tube. and secured with tantalum rivets.3. Dome made of No. 7052 glass providing electrical insulation for 20. Second radiation shield. (0.020-in. (0.51-mm) molybdenum.)thermoelements. 21. Third radiation solid. (0.020-in. (0.51-mm) molybdenum.)4. Neoprene O-ring gasket. 22
38、. Fourth radiation shield. (0.010-in. (0.25-mm) molybdenum.)5. Top plate extension (brass). 23. Liquid nitrogen trap.6. Aluminum oxide radiation shield. 24. Metal baffle plates at liquid nitrogen temperature.7. Ionization vacuum gage. 25. Liquid nitrogen chamber.8. Thermocouple vacuum gage. 26. Vacu
39、um chamber.9. No. 7052 glass tube providing electrical insulation for thermoelements. 27. Borosilicate glass window.10. Chamber for water flow during furnace operation. 28. Hole (0.045-in. (1.14-mm) diameter) for sighting with disappearing filamentpyrometer.11. Electrically insulating spacers. 29. M
40、olybdenum blackbody.12. Power supply terminal. 30. Tantalum tube.13. Removable top plate (brass). 31. Inert gas entrance.14. Tantalum spacing ring providing electrical contact between plate and 32. Tantalum rings for electrical contact.tantalum tube. 33. Removable copper plate for electrical contact
41、.15. Thermal expansion joint of tantalum tube. 34. Hex-head nut for tightening copper plate against O-ring gasket.16. Copper tubing for water cooling. 35. Bottom plate (brass).17. Auxiliary radiation shield.FIG. 1 High-Temperature Furnace (Example 1)E452 02 (2018)32)4that can be used for calibrating
42、 refractory-metal thermo-couples. Fig. 4 is a detailed drawing of the upper section of thefurnace in Fig. 3. An equalizing block containing a blackbodycavity is suspended in the central region of the furnace bymeans of support rods or wires. The mass of the support rodsor wires should be kept to a m
43、inimum to reduce heat losses byconduction. When the furnace is in operation, a sufficientlylarge region in the center of the furnace should be at a uniformtemperature to ensure that the temperature throughout theequalizing block (when all test thermocouple assemblies are inposition in the block) is
44、uniform. At temperatures greater than2000C, furnace parts made from tantalum may introducecontamination of exposed thermoelements. In this case, it maybe desirable to fabricate heated furnace components fromtungsten.7.1.2 The blackbody cavity in the equalizing block shouldbe designed in accordance w
45、ith established criteria set forth inthe literature (3-7). Such factors as interior surface texture,diameter-to-depth ratio of the blackbody cavity opening, andinternal geometry can have an appreciable effect on the spectralemissivity of the cavity.4The boldface numbers in parentheses refer to the l
46、ist of references at the end ofthis standard.(a) Nylon bushing, ( b) stainless steel support, (c) rectangular stainless steel shutter, (d) borosilicate glass window, (e) brass shutter support, ( f) shutter rotationmechanism, (g) copper lead, (h) steel housing, ( i) brass plate, (j) copper coil sprin
47、g, (k) alumina closed-end tube, (l) port, (m) O-ring gaskets, (n) copper water-cooledelectrode, (o) tantalum heater element, ( p) tantalum radiation shields, (q) water-cooling coils, (r) ceramic insulator, ( s) tantalum radiation shield, (t) adjustable clamp,(u) water out, (v) electrical leads, (w)
48、water in, and ( x) to vacuum system.FIG. 2 High-Temperature Furnace (Example 2)E452 02 (2018)47.1.3 Figs. 5-7 show three typical equalizing block designsthat are used in thermocouple calibrating furnaces. The designin Fig. 5 is used in furnaces where the standard radiationthermometer is sighted hori
49、zontally into the blackbody throughthe hole in the side of the block. This design is particularlyuseful in the calibration of bare-wire thermocouples since thelid on the blackbody (or the entire blackbody) can be anelectrically insulating material such ashafnium oxide or beryl-lium oxide. Thus, if the bare thermocouple wires should comein contact with the equalizing block, the wires will not beelectrically shorted. If this design is used in the calibration ofTypes, 2, 3, or 4 thermocouple assemblies (see 1.2), theblackbody lid can be metal since electric
