ASTM E207-08(2015)e1
(Test Method)Standard Test Method for Thermal EMF Test of Single Thermoelement Materials by Comparison with a Reference Thermoelement of Similar EMF-Temperature Properties
Standard Test Method for Thermal EMF Test of Single Thermoelement Materials by Comparison with a Reference Thermoelement of Similar EMF-Temperature Properties
SIGNIFICANCE AND USE
5.1 This test method is designed to calibrate a thermoelement at one or more test temperatures. The data obtained are sometimes referred to as initial values of emf because the time at the test temperature is limited.
5.2 This test method is employed mainly by providers of spools or coils of wire or strips of thermoelectric material. Generally more than one specimen at a time is tested, and the resultant emfs of individual thermoelements are used to match to companion thermoelements for use as thermocouples or in extension wiring.
5.3 The emf of a thermocouple comprised of two different thermoelements as tested with this test method may be determined by algebraically subtracting the emf of the negative thermoelement from the emf of the positive thermoelement at a particular temperature. The emf of a thermocouple may also be determined by the test described in Test Method E220, but Test Method E220 does not take into account the values of the emf of the individual thermoelements relative to Pt-67.
5.4 This test method is normally used for the calibration of thermocouple materials during their production or distribution, not for the accurate determination of the properties of a used thermocouple. If the test samples were subjected to previous use, the test results may not reflect the same emf as the thermocouple did while in service. For example, inhomogeneities may have been induced in the wires because of a chemical or metallurgical reaction while in service. Since emf is developed in the thermal gradient, and it is unlikely that the temperature profile along the wire under testing conditions will be the same as it was while in service, the test results may be misleading.
5.5 The test results are suitable for specification acceptance, manufacturing control, design, or research and development purposes.
SCOPE
1.1 This test method covers a test for determining the thermoelectric emf of a thermoelement versus NIST platinum 67 (Pt-67) by means of measuring the difference between the emf of the test thermoelement and the emf of a reference thermoelement (previously referred to as a secondary standard), which has a known relationship to NIST Pt-67.
1.2 This test is applicable to new thermocouple materials over the temperature ranges normally associated with thermocouples and their extension wires. The table on Suggested Upper Temperature Limits for Protected Thermocouples in Specification E230 lists the ranges associated with the letter-designated types of thermocouples. ASTM MNL-122 lists the temperature range of extension circuit materials.
1.3 This test is not applicable to stability testing or inhomogeneity testing.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 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.
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´1
Designation: E207 − 08 (Reapproved 2015) An American National Standard
Standard Test Method for
Thermal EMF Test of Single Thermoelement Materials by
Comparison with a Reference Thermoelement of Similar
EMF-Temperature Properties
This standard is issued under the fixed designation E207; 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.
ε NOTE—Editorial changes were made throughout in June 2015.
1. Scope 2. Referenced Documents
1.1 This test method covers a test for determining the 2.1 ASTM Standards:
thermoelectric emf of a thermoelement versus NIST platinum E77Test Method for Inspection and Verification of Ther-
67 (Pt-67) by means of measuring the difference between the mometers
emf of the test thermoelement and the emf of a reference E220Test Method for Calibration of Thermocouples By
thermoelement (previously referred to as a secondary Comparison Techniques
standard), which has a known relationship to NIST Pt-67. E230Specification for Temperature-Electromotive Force
(emf) Tables for Standardized Thermocouples
1.2 This test is applicable to new thermocouple materials
E344Terminology Relating to Thermometry and Hydrom-
over the temperature ranges normally associated with thermo-
etry
couples and their extension wires. The table on Suggested
E563Practice for Preparation and Use of an Ice-Point Bath
Upper Temperature Limits for Protected Thermocouples in
as a Reference Temperature
Specification E230 lists the ranges associated with the letter-
designated types of thermocouples. ASTM MNL-12 lists the
3. Terminology
temperature range of extension circuit materials.
3.1 Definitions—The terms used in this test method are
1.3 This test is not applicable to stability testing or inhomo-
defined in Terminology E344.
geneity testing.
3.2 Definitions of Terms Specific to This Standard:
1.4 The values stated in SI units are to be regarded as the
3.2.1 reference facility, n—NIST, or a testing laboratory
standard. The values given in parentheses are for information
whose physical standards are traceable to NIST or another
only.
national standards laboratory.
1.5 This standard does not purport to address all of the
3.2.2 test temperature, n—the temperature of the measuring
safety concerns, if any, associated with its use. It is the
junction.
responsibility of the user of this standard to establish appro-
3.2.2.1 Discussion—Inreportingtheresults,thevalueofthe
priate safety and health practices and determine the applica-
test temperature may be rounded off, provided the stated test
bility of regulatory limitations prior to use.
temperature is within the bounds indicated in 10.10.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
4. Summary of Test Method
ization established in the Decision on Principles for the
4.1 The emf of a thermoelement sample is determined by
Development of International Standards, Guides and Recom-
comparison to a reference thermoelement that has similar
mendations issued by the World Trade Organization Technical
Seebeck coefficients.
Barriers to Trade (TBT) Committee.
4.2 This test is conducted on one or more lengths of
specimens connected to a single length of the reference
This test method is under the jurisdiction of ASTM Committee E20 on
thermoelementatasinglepoint.Thejoinedendsareheldatthe
Temperature Measurement and is the direct responsibility of Subcommittee E20.11
on Thermocouples - Calibration.
Current edition approved May 1, 2015. Published May 2015. Originally
approved in 1962 . Last previous edition approved in 2008 as E207–08. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/E0207-08R15E01. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Manual on the Use of Thermocouples in Temperature Measurement, ASTM Standards volume information, refer to the standard’s Document Summary page on
MNL-12, Fourth Edition, ASTM, April 1993. (Revision of STP 407B). the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E207 − 08 (2015)
test temperature, and their opposite ends are held at a constant 6.4 Thespecimensandthereferencethermoelementshallbe
reference temperature. long enough to extend continuously from the measuring
junction to the reference junction.Alength of 600 to 1200 mm
4.3 The emf of the reference thermoelement relative to
(2 to 4 ft) is generally satisfactory. The exact length depends
Pt-67 at several test temperatures are provided by a reference
upon the depth of immersion in the testing medium and the
facility.
transverse size (for example, diameter of round wire, width of
4.4 The emf of the test thermoelement relative to Pt-67 is
strip) of the thermoelement.
determined by algebraically adding the measured emf to the
6.4.1 Heating of the measuring junctions shall not affect the
emf of the reference thermoelement at each test temperature.
temperatureofthereferencejunctionsduringtheperiodoftest.
5. Significance and Use
7. Reference Thermoelement
5.1 This test method is designed to calibrate a thermoele-
7.1 The reference thermoelement has its emf established
ment at one or more test temperatures. The data obtained are
relative to NIST Pt-67 over the temperature range of its
sometimes referred to as initial values of emf because the time
intended use. A specific lot of thermoelement material is
at the test temperature is limited.
usually reserved for use as reference thermoelements.
5.2 This test method is employed mainly by providers of
7.2 The emf of the reference thermoelement versus plati-
spools or coils of wire or strips of thermoelectric material.
num (Pt-67) shall conform to Specification E230 within one
Generally more than one specimen at a time is tested, and the
half the standard tolerance specified for the related thermo-
resultant emfs of individual thermoelements are used to match
couple type. For example, the tolerance for KPversus Pt-67 is
to companion thermoelements for use as thermocouples or in
6 1°C or 6 0.375% of temperature from 0 to 1260°C,
extension wiring.
whichever is greater.
5.3 The emf of a thermocouple comprised of two different
7.3 The cross section of the base metal thermoelement shall
thermoelements as tested with this test method may be deter-
be sufficiently large so that oxidation caused by the tempera-
mined by algebraically subtracting the emf of the negative
tures of testing would not significantly affect its emf over the
thermoelement from the emf of the positive thermoelement at
period of the test.
a particular temperature. The emf of a thermocouple may also
be determined by the test described in Test Method E220, but 7.4 To provide some assurance that the reserved lot is
Test Method E220 does not take into account the values of the uniforminemffromendtoend,itshallbemanufacturedinone
emf of the individual thermoelements relative to Pt-67. continuous length with no in-process welds. . Cold working of
the material after the final anneal shall be minimized.
5.4 This test method is normally used for the calibration of
7.4.1 Aspecimen from each end of the reserved lot shall be
thermocouple materials during their production or distribution,
tested using this test method. The test temperatures shall
not for the accurate determination of the properties of a used
include the extremes of the intended range of use and addi-
thermocouple. If the test samples were subjected to previous
tional test points that are no more than 260°C (500°F) apart.
use, the test results may not reflect the same emf as the
7.4.2 The emf difference between the specimens of 7.4.1 at
thermocouple did while in service. For example, inhomogene-
eachtesttemperatureshallnotexceedtheequivalentof0.33°C
itiesmayhavebeeninducedinthewiresbecauseofachemical
(0.6°F)forthatthermocoupletypeor0.05%ofthevalueofthe
or metallurgical reaction while in service. Since emf is devel-
test temperature in degrees Celsius, whichever is the greater.
oped in the thermal gradient, and it is unlikely that the
temperatureprofilealongthewireundertestingconditionswill
7.5 From the lot that meets the stated uniformity
be the same as it was while in service, the test results may be requirements, at least one unused 1m (3-ft) section shall be
misleading.
certified by a reference facility to document its emf relative to
Pt-67.Traceability shall be required in the form of a certificate
5.5 Thetestresultsaresuitableforspecificationacceptance,
issued by the reference facility.
manufacturing control, design, or research and development
7.5.1 Emf data shall be provided every 50°C (100°F) or at
purposes.
intervalsthatdonotexceed25%ofthetesttemperaturerange,
6. Test Specimen whichever is the lesser. If fewer than the aforementioned
numberofpointsaretaken,thenthedataareapplicableonlyat
6.1 Each sample shall represent one continuous spool, coil,
or near the measured temperatures, and interpolation beyond
or strip of thermoelectric material. The sample shall consist of
them should not be attempted.
two specimens, one cut from each end of the spool, coil, or
7.5.2 The emf of the reference thermoelement at intermedi-
strip. The extreme ends shall not be acceptable if they are
ate values of temperature may be determined by one of the
distortedorhavebeensubjectedtoprocessingdissimilartothe
following methods.
bulk of the spool, coil, or strip.
7.5.2.1 For the letter-designated thermocouple types, emf
6.2 Insulation or covering shall be removed with care if it
functions for thermoelements versus Pt-67 are given in Speci-
interferes with the test. Straining the test specimen shall be
fication E230. In these cases, the deviation of the reference
avoided.
thermoelementemffromthefunctionvalueisfirstcalculatedat
6.3 The specimens shall be cleaned of any extraneous the test temperatures. At an intermediate temperature, the
surface contamination. deviation of emf is calculated either by linear interpolation or
´1
E207 − 08 (2015)
NOTE 1—The preferred reference junction temperature is 0°C (32°F).
by fitting a polynomial to the deviation of emf using the
This may be approximated with an ice bath (see Practice E563),
method of least squares, and evaluating the polynomial at the
“automatic ice point” unit or a “zone box” (see MNL-12). Care should be
intermediate temperature. For the least squares method, the
exercised to maintain the reference junction temperatures for both the
number of data points shall equal or exceed twice the number
reference and test thermocouples at the same temperature.
of parameters fitted. Addition of the deviation of emf to the
function value at the intermediate temperature gives the emf
9. Measuring Junction
value of the reference thermoelement at the intermediate
9.1 The measuring junction shall consist of an electrical
temperature.
connection of the test specimens at one of their ends to the
7.5.2.2 For the thermoelements for which there is no emf
reference thermoelement. Welding is the preferred method of
function for that thermoelement versus Pt-67, a function may
joining, particularly for test temperatures above 260°C
be determined by fitting a polynomial to the emf values
(500°F).
reported by NIST for the reference thermoelement versus
9.2 The number of test specimens that may be tested at one
Pt-67, using the method of least squares. The number of data
time is limited mainly by the thermal capacity of the system.
points shall equal or exceed twice the number of parameters
The thermal conduction along the assembly of test thermoele-
fitted. Evaluation of the polynomial at the intermediate tem-
ments shall not be so large as to impair isothermal conditions
peraturegivestheemfofthereferencethermoelement.Incases
at the measuring or reference junction.
where the deviations of the fitted data from the polynomial are
significant compared to other uncertainties in the test, a
10. Test Temperature Medium
subcomponent of uncertainty shall be added to the uncertainty
budget equal to:
10.1 Normally, both the test and reference thermoelements
have the same nominal composition and consequently have
u 5 Σ E 2 E (1)
Π~ !
F G approximately the same values of Seebeck coefficients.
i fit
N
i
df
Therefore, the measured emf is expected to be small in
where:
magnitude (compared to the emf relative to Pt-67) and vary
only slightly as a function of temperature. Therefore, it is not
u = uncertainty,
E = the emf at the ith calibration temperature value of the
necessary to control the test temperature precisely.
i
reference thermoelement that has been calibrated rela-
10.2 The immersion media, insulation materials, supports,
tive to NIST Pt-67,
and adjacent materials shall not interact with or electrically
E = the emf of the fitted polynomial, and
fit
shunt the thermoelements.
N = the number of degrees of freedom in the fit = number
df
10.3 For testing in the range of−160 to−75°C (−250
of data points – number of fitted parameters.
to−100°F), a liquid nitrogen bath may be used. Refer to the
7.5.2.3 Linear interpolation of the reference thermoelement
devices and precautions inTest Method E77,Appendix X1, on
emf,ratherthanthedeviationofemf,mayalsobedone,butuse
Discussion of Apparatus for Verification of Liquid-in-Glass
of this method requires inclusion of an additional uncertainty
Thermometers and Fig. X1.3 on Comparator for Temperature
component to account for the interpolation error. This uncer-
Range from−160 to−75°C (−256 to−103°F).
tainty component may be estimated by calculating the error of
10.4 For testing in the range of −80 to +5°C (−110
linear interpolation of the emf values obtained from the emf
to+40°F), use an apparatus as depicted in Test Method E77,
functions for thermoelements versus Pt-67 in Specification
Appendix X1, on Discussion of Apparatus for Verification of
E230 or another source.This error may be as large as all other
Liquid-in-Glass Thermometers and Fig. X1.4 on Comparator
errors combined.
for Temperature Range from−80 to+5°C (−112 to+41°F),
7.6 Thesegmentofreferencethermoelementthatisusedfor
using dry ice and a suitable liquid.
each test shall be unaffected by a prior test. For example, any
10.5 For testing in the range of room temperature to 95°C
segment of a KP, EP, or JP thermoelement, exposed to
(200°F),aheatedbathusingdemineralizedwatermaybeused.
temperatures exceeding 260°C (500°F) shall not be reused.
However,ifitshowsnoevidenceofitstestenvironmentandno
10.6 In the range of 5 to 300°C (
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: E207 − 08 (Reapproved 2015) E207 − 08 (Reapproved 2015)
Standard Test Method for
Thermal EMF Test of Single Thermoelement Materials by
Comparison with a Reference Thermoelement of Similar
EMF-Temperature Properties
This standard is issued under the fixed designation E207; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial changes were made throughout in June 2015.
1. Scope
1.1 This test method covers a test for determining the thermoelectric emf of a thermoelement versus NIST platinum 67 (Pt-67)
by means of measuring the difference between the emf of the test thermoelement and the emf of a reference thermoelement
(previously referred to as a secondary standard), which has a known relationship to NIST Pt-67.
1.2 This test is applicable to new thermocouple materials over the temperature ranges normally associated with thermocouples
and their extension wires. The table on Suggested Upper Temperature Limits for Protected Thermocouples in Specification E230
lists the ranges associated with the letter-designated types of thermocouples. ASTM MNL-12 lists the temperature range of
extension circuit materials.
1.3 This test is not applicable to stability testing or inhomogeneity testing.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
E77 Test Method for Inspection and Verification of Thermometers
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
E230 Specification and Temperature-Electromotive Force (EMF) Tables for Standardized Thermocouples
E344 Terminology Relating to Thermometry and Hydrometry
E563 Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature
3. Terminology
3.1 Definitions—The terms used in this test method are defined in Terminology E344.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 reference facility, n—NIST, or a testing laboratory whose physical standards are traceable to NIST or another national
standards laboratory.
3.2.2 test temperature, n—the temperature of the measuring junction.
This test method is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.04 on
Thermocouples.
Current edition approved May 1, 2015. Published May 2015. Originally approved in 1962 . Last previous edition approved in 2008 as E207 – 08. DOI:
10.1520/E0207-08R15.10.1520/E0207-08R15E01.
Manual on the Use of Thermocouples in Temperature Measurement, ASTM MNL-12, Fourth Edition, ASTM, April 1993. (Revision of STP 407B).
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3.2.2.1 Discussion—
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
E207 − 08 (2015)
In reporting the results, the value of the test temperature may be rounded off, provided the stated test temperature is within the
bounds indicated in 10.10.
4. Summary of Test Method
4.1 The emf of a thermoelement sample is determined by comparison to a reference thermoelement that has similar Seebeck
coefficients.
4.2 This test is conducted on one or more lengths of specimens connected to a single length of the reference thermoelement at
a single point. The joined ends are held at the test temperature, and their opposite ends are held at a constant reference temperature.
4.3 The emf of the reference thermoelement relative to Pt-67 at several test temperatures are provided by a reference facility.
4.4 The emf of the test thermoelement relative to Pt-67 is determined by algebraically adding the measured emf to the emf of
the reference thermoelement at each test temperature.
5. Significance and Use
5.1 This test method is designed to calibrate a thermoelement at one or more test temperatures. The data obtained are sometimes
referred to as initial values of emf because the time at the test temperature is limited.
5.2 This test method is employed mainly by providers of spools or coils of wire or stripstrips of thermoelectric material.
Generally more than one specimen at a time is tested, and the resultant emfemfs of individual thermoelements are used to match
to companion thermoelements for use as thermocouples or in extension wiring.
5.3 The emf of a thermocouple comprised of two different thermoelements as tested with this test method may be determined
by algebraically subtracting the emf of the negative thermoelement from the emf of the positive thermoelement at a particular
temperature. The emf of a thermocouple may also be determined by the test described in Test Method E220, but Test Method E220
does not take into account the values of the emf of the individual thermoelements relative to Pt-67.
5.4 This test method is normally used for the calibration of thermocouple materials during their production or distribution, not
for the accurate determination of the properties of a used thermocouple. If the test samples were subjected to previous use, the test
results may not reflect the same emf as the thermocouple did while in service. For example, inhomogeneities may have been
induced in the wires because of a chemical or metallurgical reaction while in service. Since emf is developed in the thermal
gradient, and it is unlikely that the temperature profile along the wire under testing conditions will be the same as it was while in
service, the test results may be misleading.
5.5 The test results are suitable for specification acceptance, manufacturing control, design, or research and development
purposes.
6. Test Specimen
6.1 Each sample shall represent one continuous spool spool, coil, or coilstrip of thermoelectric material. The sample shall
consist of two specimens, one cut from each end of the spool spool, coil, or coil.strip. The extreme ends shall not be acceptable
if they are distorted or have been subjected to processing dissimilar to the bulk of the spool spool, coil, or coil.strip.
6.2 Insulation or covering shall be removed with care if it interferes with the test. Straining the test specimen shall be avoided.
6.3 The specimens shall be cleaned of any extraneous surface contamination.
6.4 The specimens and the reference thermoelement shall be long enough to extend continuously from the measuring junction
to the reference junction. A length of 600 to 1200 mm (2 to 4 ft) is generally satisfactory. The exact length depends upon the depth
of immersion in the testing medium and the transverse size (for example, diameter of round wire, width of strip) of the
thermoelement.
6.4.1 Heating of the measuring junctions shall not affect the temperature of the reference junctions during the period of test.
7. Reference Thermoelement
7.1 The reference thermoelement has its emf established relative to NIST Pt-67 over the temperature range of its intended use.
A specific lot of thermoelement material is usually reserved for use as reference thermoelements.
7.2 The emf of the reference thermoelement versus platinum (Pt-67) shall conform to Specification E230 within one half the
standard tolerance specified for the related thermocouple type. For example, the tolerance for KP versus Pt-67 is 6 1°C or 6
0.375% of temperature from 0 to 1260°C, whichever is greater.
7.3 The cross section of the base metal thermoelement shall be sufficiently large so that oxidation caused by the temperatures
of testing would not significantly affect its emf over the period of the test.
7.4 To provide some assurance that the reserved lot is uniform in emf from end to end, it shall be manufactured in one
continuous length with no in-process welds. . Cold working of the material after the final anneal shall be minimized.
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E207 − 08 (2015)
7.4.1 A specimen from each end of the reserved lot shall be tested using this test method. The test temperatures shall include
the extremes of the intended range of use and additional test points that are no more than 260°C (500°F) apart.
7.4.2 The emf difference between the specimens of 7.4.1 at each test temperature shall not exceed the equivalent of 0.33°C
(0.6°F) for that thermocouple type or 0.05 % of the value of the test temperature in degrees Celsius, whichever is the greater.
7.5 From the lot that meets the stated uniformity requirements, at least one unused 1 m (3-ft) section shall be certified by a
reference facility to document its emf relative to Pt-67. Traceability shall be required in the form of a certificate issued by the
reference facility.
7.5.1 Emf data shall be provided every 50°C (100°F) or at intervals that do not exceed 25 % of the test temperature range,
whichever is the lesser. If fewer than the aforementioned number of points are taken, then the data are applicable only at or near
the measured temperatures, and interpolation beyond them should not be attempted.
7.5.2 The emf of the reference thermoelement at intermediate values of temperature may be determined by one of the following
methods.
7.5.2.1 For the letter-designated thermocouple types, emf functions for thermoelements versus Pt-67 are given in Specification
E230. In these cases, the deviation of the reference thermoelement emf from the function value is first calculated at the test
temperature values. temperatures. At an intermediate temperature, the deviation of emf is calculated either by linear interpolation
or by fitting a polynomial to the deviation of emf using the method of least squares, and evaluating the polynomial at the
intermediate temperature. For the least squares method, the number of data points shall equal or exceed twice the number of
parameters fitted. Addition of the deviation of emf to the function value at the intermediate temperature gives the emf value of the
reference thermoelement at the intermediate temperature.
7.5.2.2 For the thermoelements for which there is no emf function for that thermoelement versus Pt-67, a function may be
determined by fitting a polynomial to the emf values reported by NIST for the reference thermoelement versus Pt-67, using the
method of least squares. The number of data points shall equal or exceed twice the number of parameters fitted. Evaluation of the
polynomial at the intermediate temperature gives the emf of the reference thermoelement. In cases where the deviations of the fitted
data from the polynomial are significant compared to other uncertainties in the test, a subcomponent of uncertainty shall be added
to the uncertainty budget equal to:
u 5 Σ E 2 E (1)
ŒF ~ ! G
i fit
N
df i
where:
u = uncertainty,
E = the emf at the ith calibration temperature value of the reference thermoelement that has been calibrated relative to NIST
i
Pt-67,
E = the emf of the fitted polynomial, and
fit
N = the number of degrees of freedom in the fit = number of data points – number of fitted parameters.
df
7.5.2.3 Linear interpolation of the reference thermoelement emf, rather than the deviation of emf, may also be done, but use
of this method requires inclusion of an additional uncertainty component to account for the interpolation error. This uncertainty
component may be estimated by calculating the error of linear interpolation of the emf values obtained from the emf functions for
thermoelements versus Pt-67 in Specification E230 or another source. This error may be as large as all other errors combined.
7.6 The segment of reference thermoelement that is used for each test shall be unaffected by a prior test. For example, any
segment of a KP, EP, or JP thermoelement, exposed to temperatures exceeding 260°C (500°F) shall not be reused. However, if it
shows no evidence of its test environment and no effects of strain, the remainder may be reused. For noble metals and their alloys,
the number of reuses depends upon the amount of strain or contamination of the segment. Noble metal reference thermoelements
should be checked for emf conformity after ten uses or less against another noble metal reference segment that was not subjected
to routine use.
8. Reference Temperature Unit
8.1 The reference temperature unit shall maintain the temperature of the reference junctions within 5°C (9°F) of the assumed
value of reference temperature. The reference temperature unit shall be designed so that the temperatures of all the reference
junctions will be isothermal.
NOTE 1—The preferred reference junction temperature is 0°C (32°F). This may be approximated with an ice bath (see Practice E563), “automatic ice
point” unit or a “zone box” (see MNL-12). Care should be exercised to maintain the reference junction temperatures for both the reference and test
thermocouples at the same temperature.
9. Measuring Junction
9.1 The measuring junction shall consist of an electrical connection of the test specimens to the reference thermoelement at one
of their ends. ends to the reference thermoelement. Welding is the preferred method of joining, particularly for test temperatures
above 260°C (500°F).
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E207 − 08 (2015)
9.2 The number of test specimens that may be tested at one time is limited mainly by the thermal capacity of the system. The
thermal conduction along the assembly of test thermoelements mustshall not be so large as to impair isothermal conditions at the
measuring or reference junction.
10. Test Temperature Medium
10.1 Normally, both the test and reference thermoelements have the same nominal composition and consequently have
approximately the same values of Seebeck coefficients. Therefore, the measured emf is expected to be small in magnitude
(compared to the emf relative to Pt-67) and vary only slightly as a function of temperature. Therefore, it is not necessary to control
the test temper
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