ASTM E207-21

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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
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Designation: E207 − 08 (Reapproved 2015) E207 − 21 An American National Standard
Standard Test Method for
Thermal EMF Test of Single Thermoelement Materials by
Comparison with a With 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 electromotive force (emf) of a thermoelement versus
NIST National Instruments of Standards and Technology (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 method 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 E230E230/E230M lists the ranges associated with the letter-designated types of thermocouples. ASTM MNL-
12MNL12 lists the temperature range of extension circuit materials.
1.3 This test method 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. after
SI units are provided for information only and are not considered standard.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E77 Test Method for Inspection and Verification of Thermometers
This test method is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.11 on
Thermocouples - Calibration.
Current edition approved May 1, 2015May 1, 2021. Published May 2015July 2021. Originally approved in 1962 . Last previous edition approved in 20082015 as
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E207 – 08.E207 – 08 (2015) . DOI: 10.1520/E0207-08R15E01.10.1520/E0207-21.
Manual on the Use of Thermocouples in Temperature Measurement, ASTM MNL-12,Fourth Edition, MNL12, Fourth Edition, ASTM, April ASTM International, 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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E207 − 21
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
E230E230/E230M Specification for 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.
3.1 Definitions:
3.1.1 The terms used in this test method are defined in Terminology E344.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 lot, n—a quantity of thermocouple material manufactured from the same batch, assembled and processed together under
controlled production conditions having uniform characteristics.
3.2.2 reference facility, n—NIST, or a testing laboratory whose physical standards are traceable to NIST or another national
standards laboratory.
3.2.3 test temperature, n—the temperature of the measuring junction.
3.2.3.1 Discussion—
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 method 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 areis 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 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
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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, coil, or strip of thermoelectric material. The sample shall consist of two
specimens, one cut from each end of the spool, coil, or 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, coil, or 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 E230E230/E230M 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% 61.1 °C or 60.375 % of temperature from 0 to 1260°C,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.minimized.
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)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)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)50 °C (90 °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 extrapolation beyond the end points 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.
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7.5.2.1 For the letter-designated thermocouple types, emf functions for thermoelements versus Pt-67 are given in Specification
E230E230/E230M. In these cases, the deviation of the reference thermoelement emf from the function value is first calculated at
the test 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)
Π~ !
F i fit G
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 E230E230/E230M 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)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 lessfewer 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)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).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).MNL12 ). 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 at one of their ends to the reference
thermoelement. Welding is the preferred method of joining, particularly for test temperatures above 260°C (500°F).260 °C
(500 °F).
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 shall not be so large as to impair isothermal conditions at the
measuring or reference junction.
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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 temperature precisely.
10.2 The immersion media, insulation materials, supports, and adjacent materials shall not interact with or electrically shunt the
thermoelements.
10.3 For testing in the range of −160 to −75°C (−250 to −100°F),to −75 °C (−256 to −103 °F), a liquid nitrogen bath may be used.
Refer to the devices and precautions in Test Method E77, Appendix X1, on Discussion of Apparatus for Verification of
Liquid-in-Glass Thermometers and Fig. X1.3 on Comparator for Temperature Range from −160 to −75°Cto −75 °C (−256
to −103°F).to −103 °F).
10.4 For testing in the range of −80 to +5°C (−110 to +40°F),to +5 °C (−112 to +41 °F), use an apparatus as depicted in Test
Method E77, may be used, Appendix X1, on Discussion of Apparatus for Verification of Liquid-in-Glass Thermometers and Fig.
X1.4 on Comparator for Temperature Range from −80 to +5°Cto +5 °C (−112 to +41°F),to +41 °F), using dry ice and a suitable
liquid.
10.5 For testing in the range of room temperature to 95°C (200°F),95 °C (200 °F), a heated bath using demineralized water may
be used.
10.6 In the range of 5 to 300°C (40300 °C (41 to 600°F),572 °F), a stirred bath of an oil with a flash point higher than the test
temperature may be used. Refer to Test Method E77, Appendix X1, on Discussion of Apparatus for Verification of Liquid-in-Glass
Thermometers and Fig. X1.6(b) on Alternative Designs.
10.7 For testing at or above 100°C (200°F),100 °C (212 °F), an electrically-heated laboratory-type wire-wound tube furnace is
generallymay be used. The atmosphere inside the tube shall be air, and the ends shall not both be sealed airtight. Other atmospheres
may be used as agreed upon between the producer and purchaser. Other options may be used as a temperature media, such as a
stirred liquid baths, uniformly heated metal blocks, and dry fluidized baths, are suitable temperature comparison environment
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