Standard Test Method for Calibration of Refractory Metal Thermocouples Using a Radiation Thermometer

SIGNIFICANCE AND USE
5.1 This test method is intended to be used by wire producers and thermocouple manufacturers for certification of refractory metal thermocouples. It is intended to provide a consistent method for calibration of refractory metal thermocouples referenced to a calibrated radiation thermometer. Uncertainty in calibration and operation of the radiation thermometer, and proper construction and use of the test furnace are of primary importance.  
5.2 Calibration establishes the temperature-emf relationship for a particular thermocouple under a specific temperature and chemical environment. However, during high temperature calibration or application at elevated temperatures in vacuum, oxidizing, reducing or contaminating environments, and depending on temperature distribution, local irreversible changes may occur in the Seebeck Coefficient of one or both thermoelements. If the introduced inhomogeneities are significant, the emf from the thermocouple will depend on the distribution of temperature between the measuring and reference junctions.  
5.3 At high temperatures, the accuracy of refractory metal thermocouples may be limited by electrical shunting errors through the ceramic insulators of the thermocouple assembly. This effect may be reduced by careful choice of the insulator material, but above approximately 2100 °C, the electrical shunting errors may be significant even for the best insulators available.
SCOPE
1.1 This test method covers the calibration of refractory metal thermocouples using a radiation thermometer as the standard instrument. This test method is intended for use with types of thermocouples that cannot be exposed to an oxidizing atmosphere. These procedures are appropriate for thermocouple calibrations at temperatures above 800 °C (1472 °F).  
1.2 The calibration method is applicable to the following thermocouple assemblies:  
1.2.1 Type 1—Bare-wire thermocouple assemblies in which vacuum or an inert or reducing gas is the only electrical insulating medium between the thermoelements.  
1.2.2 Type 2—Assemblies in which loose fitting ceramic insulating pieces, such as single-bore or double-bore tubes, are placed over the thermoelements.  
1.2.3 Type 2A—Assemblies in which loose fitting ceramic insulating pieces, such as single-bore or double-bore tubes, are placed over the thermoelements, permanently enclosed and sealed in a loose fitting metal or ceramic tube.  
1.2.4 Type 3—Swaged assemblies in which a refractory insulating powder is compressed around the thermoelements and encased in a thin-walled tube or sheath made of a high melting point metal or alloy.  
1.2.5 Type 4—Thermocouple assemblies in which one thermoelement is in the shape of a closed-end protection tube and the other thermoelement is a solid wire or rod that is coaxially supported inside the closed-end tube. The space between the two 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 the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

Status
Historical
Publication Date
30-Apr-2013
Current Stage
Ref Project

Relations

Buy Standard

Standard
ASTM E452-02(2013) - Standard Test Method for Calibration of Refractory Metal Thermocouples Using a Radiation Thermometer
English language
14 pages
sale 15% off
Preview
sale 15% off
Preview

Standards Content (Sample)


NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E452 − 02 (Reapproved 2013)
Standard Test Method for
Calibration of Refractory Metal Thermocouples Using a
Radiation Thermometer
This standard is issued under the fixed designation E452; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This test method covers the calibration of refractory
mendations issued by the World Trade Organization Technical
metal thermocouples using a radiation thermometer as the
Barriers to Trade (TBT) Committee.
standard instrument. This test method is intended for use with
types of thermocouples that cannot be exposed to an oxidizing
2. Referenced Documents
atmosphere. These procedures are appropriate for thermo-
couple calibrations at temperatures above 800°C (1472°F).
2.1 ASTM Standards:
E344Terminology Relating to Thermometry and Hydrom-
1.2 The calibration method is applicable to the following
etry
thermocouple assemblies:
E563Practice for Preparation and Use of an Ice-Point Bath
1.2.1 Type 1—Bare-wire thermocouple assemblies in which
as a Reference Temperature
vacuum or an inert or reducing gas is the only electrical
E988Temperature-Electromotive Force (EMF) Tables for
insulating medium between the thermoelements.
Tungsten-Rhenium Thermocouples (Withdrawn 2011)
1.2.2 Type 2—Assemblies in which loose fitting ceramic
E1256Test Methods for Radiation Thermometers (Single
insulatingpieces,suchassingle-boreordouble-boretubes,are
Waveband Type)
placed over the thermoelements.
E1751Guide for Temperature Electromotive Force (EMF)
1.2.3 Type 2A—Assemblies in which loose fitting ceramic
Tables for Non-Letter Designated Thermocouple Combi-
insulatingpieces,suchassingle-boreordouble-boretubes,are
nations (Withdrawn 2009)
placed over the thermoelements, permanently enclosed and
sealed in a loose fitting metal or ceramic tube.
3. Terminology
1.2.4 Type 3—Swaged assemblies in which a refractory
insulating powder is compressed around the thermoelements
3.1 Definitions:
and encased in a thin-walled tube or sheath made of a high
3.1.1 For definitions of terms used in this test method see
melting point metal or alloy.
Terminology E344.
1.2.5 Type 4—Thermocouple assemblies in which one ther-
3.1.2 radiation thermometer, n—radiometer calibrated to
moelement is in the shape of a closed-end protection tube and
indicate the temperature of a blackbody.
the other thermoelement is a solid wire or rod that is coaxially
3.1.2.1 Discussion—Radiationthermometersincludeinstru-
supported inside the closed-end tube. The space between the
ments having the following or similar names: (1) optical
twothermoelementscanbefilledwithaninertorreducinggas,
radiation thermometer, (2) photoelectric pyrometer, ( 3) single
or with ceramic insulating materials, or kept under vacuum.
wavelength automatic thermometer, (4) disappearing filament
1.3 This standard does not purport to address all of the
pyrometer, (5) dual wavelength pyrometer or ratio radiation
safety concerns, if any, associated with its use. It is the
thermometer, (6) visual optical thermometer, (7) infrared
responsibility of the user of this standard to establish appro-
thermometer, (8) infrared pyrometer, and permutations on the
priate safety and health practices and determine the applica-
terms above as well as some manufacturer-specific names.
bility of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1 2
This test method is under the jurisdiction of ASTM Committee E20 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Temperature Measurementand is the direct responsibility of Subcommittee E20.11 contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
on Thermocouples - Calibration. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved May 1, 2013. Published May 2013. Originally the ASTM website.
approved in 1972. Last previous edition approved in 2007 as E452–02 (2007). The last approved version of this historical standard is referenced on
DOI: 10.1520/E0452-02R13. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E452 − 02 (2013)
3.2.1 automatic radiation thermometer, n— radiation ther- its calibration becomes questionable and the uncertainty in the
mometer whose temperature reading is determined by elec- bias of the calibration increases.
tronic means.
NOTE1—Disappearingfilamentpyrometersaresomewhatlesssensitive
3.2.2 disappearing filament pyrometer, n— radiation ther-
than many of the thermocouples used above 800°C (1472°F). The
mometer that requires an observer to match visually the
advantages of physical separation of the disappearing filament pyrometer
from the test assembly may still justify its use over use of a standard
brightness of a heated filament mounted inside the radiation
thermocouple.
thermometer to that of the measured object.
3.2.3 equalizing block, n—object, usually metal, that when
5. Significance and Use
placed in a nonuniform temperature region, has greater tem-
perature uniformity (due to its relatively high thermoconduc- 5.1 This test method is intended to be used by wire
tivity and mass) than the medium surrounding the object.
producers and thermocouple manufacturers for certification of
refractory metal thermocouples. It is intended to provide a
3.2.4 spectral emissivity, n—ratio of the spectral radiance at
consistent method for calibration of refractory metal thermo-
a point on a particular specimen and in a particular direction
from that point to that emitted by a blackbody at the same couples referenced to a calibrated radiation thermometer.
Uncertainty in calibration and operation of the radiation
temperature.
thermometer, and proper construction and use of the test
3.2.5 spectral radiance, n—powerradiatedbyaspecimenin
furnace are of primary importance.
a particular direction, per unit wavelength, per unit projected
area of the specimen, and per unit solid angle.
5.2 Calibration establishes the temperature-emf relationship
3.2.6 spectral response, n—signal detected by a radiometer for a particular thermocouple under a specific temperature and
at a particular wavelength of incident radiation, per unit power
chemical environment. However, during high temperature
of incident radiation.
calibration or application at elevated temperatures in vacuum,
oxidizing, reducing or contaminating environments, and de-
3.2.7 test thermocouple, n—thermocouple that is to have its
pending on temperature distribution, local irreversible changes
temperature-emf relationship determined by reference to a
may occur in the Seebeck Coefficient of one or both thermo-
temperature standard.
elements.Iftheintroducedinhomogeneitiesaresignificant,the
3.2.8 thermocouple calibration point, n— temperature, es-
emf from the thermocouple will depend on the distribution of
tablished by a standard, at which the emf developed by a
temperature between the measuring and reference junctions.
thermocouple is determined.
5.3 At high temperatures, the accuracy of refractory metal
4. Summary of Test Method
thermocouples may be limited by electrical shunting errors
4.1 The thermocouple is calibrated by determining the through the ceramic insulators of the thermocouple assembly.
temperature of its measuring junction with a radiation ther- This effect may be reduced by careful choice of the insulator
mometer and recording the emf of the thermocouple at that material, but above approximately 2100°C, the electrical
temperature. The measuring junction of the thermocouple is
shunting errors may be significant even for the best insulators
placed in an equalizing block containing a cavity which available.
approximates blackbody conditions. The radiation thermom-
eter is sighted on the cavity in the equalizing block and the
6. Sources of Error
blackbody temperature or true temperature of the block,
6.1 The most prevalent sources of error (Note 2) in this
including the measuring junction, is determined.
method of calibration are: (1) improper design of the black-
4.2 Since the spectral emissivity of the radiation emanating
bodyenclosure,(2)severetemperaturegradientsinthevicinity
from a properly designed blackbody is considered unity (one)
of the blackbody enclosure, ( 3) heat conduction losses along
for all practical purposes, no spectral emissivity corrections
the thermoelements, and ( 4) improper alignment of the
need be applied to optical pyrometer determinations of the
radiationthermometerwithrespecttotheblackbodycavityand
blackbody temperature.
unaccounted transmission losses along the optical path of the
radiation thermometer.
4.3 Although the use of a radiation thermometer (Note 1)is
less may require more effort and more complex apparatus to
NOTE 2—These are exclusive of any errors that are made in the
achieve a sensitivity equivalent to that of commonly used
radiation thermometer measurements or the thermocouple-emf measure-
thermocouples, a radiation thermometer has the advantage of
ments.
being physically separated from the test assembly; thus, its
calibration is not influenced by the temperatures and atmo-
7. Apparatus
spheres in the test chamber. By comparison, a standard
7.1 Furnace:
thermocouple that is used to calibrate another thermocouple
7.1.1 Thecalibrationfurnaceshouldbedesignedsothatany
mustbesubjectedtothetemperaturesatwhichthecalibrations
temperature within the desired calibration temperature range
are performed and in some cases must be exposed to the
environment that is common to the test thermocouple. If a can be maintained constant within a maximum change of 1°C
(1.8°F) per minute in the equalizing block over the period of
standard thermocouple is exposed to high temperatures or
contaminating environments, or both, for long periods of time, any observation. Figs. 1-3 show three types of furnaces (1 and
E452 − 02 (2013)
1. 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 into a cylinder
2. 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. 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. 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 sighting with disappearing filament
pyrometer.
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 electrical 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-Temperature Furnace (Example 1)
E452 − 02 (2013)
(a) Nylon bushing, ( b) stainless steel support, (c) rectangular stainless steel shutter, (d) borosilicate glass window, (e) brass shutter support, ( f) shutter rotation
mechanism,(g) copperlead,(h) steelhousing,(i) brassplate,(j) coppercoilspring,(k) aluminaclosed-endtube,(l) port,(m) O-ringgaskets,(n) copperwater-cooled
electrode, (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 vacuum system.
FIG. 2 High-Temperature Furnace (Example 2)
2) that can be used for calibrating refractory-metal thermo- equalizingblock(whenalltestthermocoupleassembliesarein
couples.Fig.4isadetaileddrawingoftheuppersectionofthe position in the block) is uniform.At temperatures greater than
furnace in Fig. 3.An equalizing block containing a blackbody 2000°C, furnace parts made from tantalum may introduce
cavity is suspended in the central region of the furnace by
contamination of exposed thermoelements. In this case, it may
means of support rods or wires. The mass of the support rods
be desirable to fabricate heated furnace components from
or wires should be kept to a minimum to reduce heat losses by
tungsten.
conduction. When the furnace is in operation, a sufficiently
7.1.2 The blackbody cavity in the equalizing block should
large region in the center of the furnace should be at a uniform
be designed in accordance with established criteria set forth in
temperature to ensure that the temperature throughout the
the literature (3-7). Such factors as interior surface texture,
diameter-to-depth ratio of the blackbody cavity opening, and
4 internalgeometrycanhaveanappreciableeffectonthespectral
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. emissivity of the cavity.
E452 − 02 (2013)
FIG. 4 Upper Section of Furnace (Example 3)
(A) Disappearing filament pyrometer
(B) Sight window
(C) Gas inlet
(D) Water cooling
(E) Stainless steel shell
(F) Tungsten heat shield material. Material Safety Data Sheets and precautions in
(G) Tungsten heater
handling this toxic substance should be obtained from the
(H) Support rods
supplier.)
(J) Equalizer block (blackbody)
7.1.4 The designs in Figs. 6 and 7 are used in furnaces
(K) Refractory brick
(L) Gallium alloy electrical contact
where the standard radiation thermometer is sighted vertically
(M) Gas outlet
into the blackbody cavity. In cases whe
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.