1、Designation: E 452 02 (Reapproved 2007)Standard Test Method forCalibration of Refractory Metal Thermocouples Using aRadiation Thermometer1This standard is issued under the fixed designation E 452; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 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 This test method covers the calibration of refractorymetal thermocouples using a radiation
3、thermometer 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 800 C (1472 F).1.2 The calibration method is applicable to th
4、e followingthermocouple 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 tu
5、bes, 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
6、a refractoryinsulating 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
7、solid 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, ass
8、ociated with its use. It is theresponsibility 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:2E 344 Terminology Relating to Thermometry and Hydrom-etr
9、yE 563 Practice for Preparation and Use of an Ice-Point Bathas a Reference TemperatureE 988 Temperature-Electromotive Force (EMF) Tables forTungsten-Rhenium ThermocouplesE 1256 Test Methods for Radiation Thermometers (SingleWaveband Type)E 1751 Guide for Temperature Electromotive Force (EMF)Tables f
10、or Non-Letter Designated Thermocouple Combi-nations3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method seeTerminology E 344.3.1.2 radiation thermometer, nradiometer calibrated toindicate the temperature of a blackbody.3.1.2.1 DiscussionRadiation thermometers include
11、 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 radiationthermometer, (6) visual optical thermometer, (7) infrare
12、dthermometer, (8) infrared pyrometer, and permutations on theterms above as well as some manufacturer-specific names.3.2 Definitions of Terms Specific to This Standard:3.2.1 automatic radiation thermometer, nradiation ther-mometer whose temperature reading is determined by elec-tronic means.3.2.2 di
13、sappearing filament pyrometer, nradiation ther-mometer that requires an observer to match visually the1This test method is under the jurisdiction of ASTM Committee E20 onTemperature Measurement and is the direct responsibility of Subcommittee E20.04on Thermocouples.Current edition approved May 1, 20
14、07. Published June 2007. Originallyapproved in 1972. Last previous edition approved in 2002 as E 452 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 standard
15、s Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.brightness of a heated filament mounted inside the radiationthermometer to that of the measured object.3.2.3 equalizing block, nobject, usuall
16、y metal, that whenplaced in a nonuniform temperature region, has greater tem-perature uniformity (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 par
17、ticular directionfrom that point to that emitted by a blackbody at the sametemperature.3.2.5 spectral radiance, npower radiated by a specimenin a 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
18、 radiometerat a particular wavelength of incident radiation, per unit powerof incident radiation.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, ntemperature, es-tablished by
19、 a standard, at which the emf developed by athermocouple is determined.4. Summary of Test 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 junctio
20、n of the thermocouple isplaced in an equalizing block containing a cavity whichapproximates 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.
21、4.2 Since the spectral emissivity of the radiation emanatingfrom a properly designed blackbody 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 th
22、ermometer (Note 1)isless may require more effort and more complex apparatus toachieve a 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 temperatu
23、res and atmo-spheres in the test chamber. By comparison, a standardthermocouple that is 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 a
24、standard thermocouple is exposed to high temperatures orcontaminating environments, or 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 sensi-tive than many of the
25、thermocouples used above 800 C (1472 F). Theadvantages of physical separation of the disappearing 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
26、 manufacturers for certification ofrefractory metal thermocouples. It is intended to provide 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 constru
27、ction and use of the testfurnace are of primary importance.5.2 Calibration establishes the temperature-emf relationshipfor a particular thermocouple under a specific temperature andchemical environment. However, during high temperaturecalibration or application at elevated temperatures in vacuum,oxi
28、dizing, reducing or contaminating environments, and de-pending on temperature distribution, 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 o
29、ftemperature between the measuring and reference junctions.5.3 At high temperatures, the accuracy 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 insulatormate
30、rial, but above approximately 2100 C, the electricalshunting errors may be significant even 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 g
31、radients in the vicinityof the blackbody enclosure, (3) heat conduction losses alongthe thermoelements, 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
32、exclusive of any errors that are made in theradiation thermometer measurements or the thermocouple-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 max
33、imum change of 1 C(1.8 F) per minute in the equalizing block over the period ofany observation. Figs. 1-3 show three types of furnaces (1 and2)3that can be used for calibrating refractory-metal thermo-couples. Fig. 4 is a detailed drawing of the upper section of thefurnace in Fig. 3. An equalizing b
34、lock 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 minimum to reduce heat losses byconduction. When the furnace is in operation, a sufficientlylarge region in the center of the
35、 furnace should be at a uniform3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E 452 02 (2007)21. Caps for making vacuum tight seals around the thermoelements. A cylinder 18. Furnace shell (brass).type neoprene gasket is compressed around the thermoele
36、ments. 19. First radiation shield. 0.020-in. (0.51-mm) tantalum sheet rolled into 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
37、 radiation solid. (0.020-in. (0.51-mm) molybdenum.)4. Neoprene O-ring gasket. 22. 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. Ionizatio
38、n vacuum gage. 25. Liquid nitrogen chamber.8. Thermocouple vacuum gage. 26. Vacuum 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 sightin
39、g with disappearing filamentpyrometer.11. Electrically insulating spacers. 29. Molybdenum 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 ele
40、ctrical contact.tantalum tube. 33. Removable copper plate for electrical contact.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-T
41、emperature Furnace (Example 1)E 452 02 (2007)3temperature to ensure that the temperature throughout theequalizing block (when all test thermocouple assemblies are inposition in the block) is uniform. At temperatures greater than2000 C, furnace parts made from tantalum may introducecontamination of e
42、xposed 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 with established criteria set forth inthe literature (4-8). Such factors as interior surface texture,diameter
43、-to-depth ratio of the blackbody cavity opening, andinternal geometry can have an appreciable effect on the spectralemissivity of the cavity.7.1.3 Figs. 5-7 show three typical equalizing block designsthat are used in thermocouple calibrating furnaces. The designin Fig. 5 is used in furnaces where th
44、e standard radiationthermometer is sighted horizontally 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
45、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 e
46、lectrical insulation between(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 spring, (k) alumina close
47、d-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) water in, and (x) to v
48、acuum system.FIG. 2 High-Temperature Furnace (Example 2)E 452 02 (2007)4the thermoelements is included as part of the assembly.(WarningBeryllium oxide should be considered a hazardousmaterial. Material Safety Data Sheets and precautions inhandling this toxic substance should be obtained from thesupp
49、lier.)7.1.4 The designs in Figs. 6 and 7 are used in furnaceswhere the standard radiation thermometer is sighted verticallyinto the blackbody cavity. In cases where it is necessary tocalibrate a number of thermocouples during one calibration runor to calibrate thermocouple assemblies that are large indiameter and mass, the equalizing block designs in Figs. 6 and7 are appropriate. If the thermocouple assemblies being testedin these types of equalizing blocks are massive and can conducta considerable amount of heat away from the block, theblackbody cavity
