ASTM E207-00
(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
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.
This test method is employed mainly by providers of spools or coils of wire or strip of thermoelectric material. Generally more than one specimen at a time is tested, and the resultant emf of individual thermoelements are used to match to companion thermoelements for use as thermocouples or in extension wiring.
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 E 220, but Test Method E 220 does not take into account the values of the emf of the individual thermoelements relative to Pt-67.
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.
The test results are suitable for specification acceptance, manufacturing control, design, or research and development purposes.
SCOPE
1.1 This 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 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.
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Standards Content (Sample)
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Designation:E207–00
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope (EMF) Tables for Standardized Thermocouples
E344 Terminology Relating to Thermometry and Hydrom-
1.1 This test method covers a test for determining the
etry
thermoelectric emf of a thermoelement versus NIST platinum
E563 PracticeforPreparationandUseofanIce-PointBath
67 (Pt-67) by means of measuring the difference between the
as a Reference Temperature
emf of the test thermoelement and the emf of a reference
thermoelement (previously referred to as a secondary stan-
3. Terminology
dard), which has a known relationship to NIST Pt-67.
3.1 Definitions—The terms used in this test method are
1.2 This test is applicable to thermocouple materials over
defined in Terminology E344.
the temperature ranges normally associated with thermo-
3.2 Definitions of Terms Specific to This Standard:
couples and their extension wires. The table on Suggested
3.2.1 reference facility, n—NIST, or a testing laboratory
Upper Temperature Limits for Protected Thermocouples in
whose physical standards are traceable to NIST or another
Specification E230 lists the ranges associated with the letter-
2 national standards laboratory.
designated types of thermocouples. ASTM MNL-12 lists the
3.2.2 test temperature, n—thetemperatureofthemeasuring
temperature range of extension circuit materials.
junction.
1.3 This test is not applicable to stability testing or inhomo-
3.2.2.1 Discussion—Inreportingtheresults,thevalueofthe
geneity testing.
test temperature may be rounded off, provided the stated test
1.4 The values stated in SI units are to be regarded as the
temperature is within the bounds indicated in 10.10.
standard. The values given in parentheses are for information
only.
4. Summary of Test Method
1.5 This standard does not purport to address all of the
4.1 The emf of a thermoelement sample is determined by
safety concerns, if any, associated with its use. It is the
comparison to a reference thermoelement that has similar
responsibility of the user of this standard to establish appro-
Seebeck coefficients.
priate safety and health practices and determine the applica-
4.2 This test is conducted on one or more lengths of
bility of regulatory limitations prior to use.
specimens connected to a single length of the reference
2. Referenced Documents thermoelementatasinglepoint.Thejoinedendsareheldatthe
test temperature, and their opposite ends are held at a constant
2.1 ASTM Standards:
reference temperature.
E77 Test Method for Inspection and Verification of Ther-
3 4.3 The emf of the reference thermoelement relative to
mometers
Pt-67 at several test temperatures are provided by a reference
E220 Test Method for Calibration of Thermocouples by
3 facility.
Comparison Techniques
4.4 The emf of the test thermoelement relative to Pt-67 is
E230 Specification for Temperature-Electromotive Force
determined by algebraically adding the measured emf to the
emf of the reference thermoelement at each test temperature.
This test method is under the jurisdiction of ASTM Committee E20 on
5. Significance and Use
Temperature Measurement and is the direct responsibility of Subcommittee E20.04
5.1 This test method is designed to calibrate a thermoele-
on Thermocouples.
Current edition approvedAug. 10, 2000. Published September 2000. Originally
ment at one or more test temperatures. The data obtained are
published as E207–62 T. Last previous edition E207–96.
sometimes referred to as initial values of emf because the time
Manual on the Use of Thermocouples in Temperature Measurement, ASTM
at the test temperature is limited.
MNL-12, Fourth Edition, ASTM, April 1993. (Revision of STP 407B).
Annual Book of ASTM Standards, Vol 14.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E207
5.2 This test method is employed mainly by providers of half the standard tolerance specified for the related thermo-
spools or coils of wire or strip of thermoelectric material. couple type. For example, the tolerance for KPversus Pt-67 is
Generally more than one specimen at a time is tested, and the 61°Cor 6 0.375% of temperature from 0 °C to 1260 °C,
resultant emf of individual thermoelements are used to match whichever is greater.
to companion thermoelements for use as thermocouples or in
7.3 The cross section of the base metal thermoelement shall
extension wiring.
be sufficiently large so that oxidation caused by the tempera-
5.3 The emf of a thermocouple comprised of two different
tures of testing would not significantly affect its emf over the
thermoelements as tested with this test method may be deter-
period of the test.
mined by algebraically subtracting the emf of the negative
7.4 To provide some assurance that the reserved lot is
thermoelement from the emf of the positive thermoelement at
uniform in emf from end to end, that lot shall be taken from a
a particular temperature. The emf of a thermocouple may also
single source (ingot), shall be manufactured in one continuous
be determined by the test described in Test Method E220, but
length with no in-process welds, and efforts made to minimize
TestMethodE220doesnottakeintoaccountthevaluesofthe
cold working the material.
emf of the individual thermoelements relative to Pt-67.
7.4.1 Aspecimen from each end of the reserved lot shall be
5.4 This test method is normally used for the calibration of
tested using this test method. The test temperatures shall
thermocouple materials during their production or distribution,
include the extremes of the intended range of use and addi-
not for the accurate determination of the properties of a used
tional test points that are no more than 260 °C (500 °F) apart.
thermocouple. If the test samples were subjected to previous
7.4.2 The emf difference between the specimens of 7.4.1 at
use, the test results may not reflect the same emf as the
eachtesttemperatureshallnotexceedtheequivalentof0.33°C
thermocouple did while in service. For example, inhomogene-
(0.6 °F) for that thermocouple type or 0.05% of the value of
itiesmayhavebeeninducedinthewiresbecauseofachemical
the test temperature in degrees Celsius, whichever is the
or metallurgical reaction while in service. Since emf is devel-
greater.
oped in the thermal gradient, and it is unlikely that the
7.5 From the lot that meets the stated uniformity require-
temperatureprofilealongthewireundertestingconditionswill
ments, at least one unused 1-m (3-ft) section shall be certified
be the same as it was while in service, the test results may be
by a reference facility to document its emf relative to Pt-67.
misleading.
Traceabilityshallberequiredintheformofacertificateissued
5.5 Thetestresultsaresuitableforspecificationacceptance,
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,
whichever is the lesser. If fewer than the aforementioned
6. Test Specimen
numberofpointsaretaken,thenthedataareapplicableonlyat
6.1 Eachsampleshallrepresentonecontinuousspoolorcoil
or near the measured temperatures, and interpolation beyond
of thermoelectric material. The sample shall consist of two
them should not be attempted.
specimens, one cut from each end of the spool or coil. The
7.5.2 The emf of the reference thermoelement at intermedi-
extreme ends shall not be acceptable if they are distorted or
ate values of temperature may be determined by one of the
have been subjected to processing dissimilar to the bulk of the
following methods.
spool or coil.
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
thetesttemperaturevalues.Atanintermediatetemperature,the
surface contamination.
deviation of emf is calculated either by linear interpolation or
6.4 Thespecimensandthereferencethermoelementshallbe
by fitting a polynomial to the deviation of emf using the
long enough to extend continuously from the measuring
method of least squares, and evaluating the polynomial at the
junction to the reference junction.Alength of 600 to 1200 mm
intermediate temperature. For the least squares method, the
(2 to 4 ft) is generally satisfactory. The exact length depends
number of data points shall equal or exceed twice the number
upon the depth of immersion in the testing medium and the
of parameters fitted. Addition of the deviation of emf to the
transverse size (for example, diameter of round wire, width of
function value at the intermediate temperature gives the emf
strip) of the thermoelement.
value of the reference thermoelement at the intermediate
6.4.1 Heating of the measuring junctions shall not affect the
temperature.
temperatureofthereferencejunctionsduringtheperiodoftest.
7.5.2.2 For the thermoelements for which there is no emf
7. Reference Thermoelement
function for that thermoelement versus Pt-67, a function may
7.1 The reference thermoelement has its emf established be determined by fitting a polynomial to the emf values
relative to NIST Pt-67 over the temperature range of its reported by NIST for the reference thermoelement versus
intended use. A specific lot of thermoelement material is Pt-67, using the method of least squares. The number of data
usually reserved for use as reference thermoelements. points shall equal or exceed twice the number of parameters
7.2 The emf of the reference thermoelement versus plati- fitted. Evaluation of the polynomial at the intermediate tem-
num (Pt-67) shall conform to Specification E230 within one peraturegivestheemfofthereferencethermoelement.Incases
E207
where the deviations of the fitted data from the polynomial are case, the emf of the test thermoelements versus the reference
significant compared to other uncertainties in the test, a thermoelement must be determined between the ice point and
subcomponent of uncertainty shall be added to the uncertainty the alternate reference temperature. These emf shall be alge-
budget equal to: braically added to the respective emf obtained at the test
temperatures, in order to accurately determine their emf versus
u 5 @ ~E – E ! # (1)
Π( the ice point. See Section 13 for these calculations.
i fit
N
df i
9. Measuring Junction
where:
u = uncertainty,
9.1 The measuring junction shall consist of an electrical
E = the emf at the ith calibration temperature value of
i
connection of the test specimens to the reference thermoele-
thereferencethermoelementthathasbeencalibrated
ment at one of their ends. Welding is the preferred method of
relative to NIST Pt-67,
joining, particularly for test temperatures above 260 °C (500
E = the emf of the fitted polynomial, and
fit
°F).
N = the number of degrees of freedom in the fit =
df
9.2 The number of test specimens that may be tested at one
numberofdatapoints–numberoffittedparameters.
time is limited mainly by the thermal capacity of the system.
7.5.2.3 Linear interpolation of the reference thermoelement
The thermal conduction along the assembly of test thermoele-
emf,ratherthanthedeviationofemf,mayalsobedone,butuse
ments must not be so large as to impair isothermal conditions
of this method requires inclusion of an additional uncertainty
at the measuring or reference junction.
component to account for the interpolation error. This uncer-
tainty component may be estimated by calculating the error of
10. Test Temperature Medium
linear interpolation of the emf values obtained from the emf
10.1 Normally, both the test and reference thermoelements
functions for thermoelements versus Pt-67 in Specification
have the same nominal composition and consequently have
E230oranothersource.Thiserrormaybeaslargeasallother
approximately the same values of Seebeck coefficients. There-
errors combined.
fore, the measured emf is expected to be small in magnitude
7.6 Thesegmentofreferencethermoelementthatisusedfor
(compared to the emf relative to Pt-67) and vary only slightly
each test shall be unaffected by a prior test. For example, any
as a function of temperature. Therefore, it is not necessary to
segment of KP, EP, or JP thermoelement, exposed to tempera-
control the test temperature precisely.
tures exceeding 260 °C (500 °F) shall not be reused. However,
10.2 The immersion media, insulation materials, supports,
ifitshowsnoevidenceofitstestenvironmentandnoeffectsof
and adjacent materials shall not interact with or electrically
strain,theremaindermaybereused.Fornoblemetalsandtheir
shunt the thermoelements.
alloys,thenumberofreusesdependsupontheamountofstrain
10.3 For testing in the range of−160 to−75 °C (−250
or contamination of the segment. Noble metal reference
to−100 °F), a liquid nitrogen bath may be used. Refer to the
thermoelements should be checked for emf conformity after
devicesandprecautionsinTestMethodE77,AppendixX1,on
ten uses or less against another noble metal reference segment
Discussion of Apparatus for Verification of Liquid-in-Glass
that was not subjected to routine use.
Thermometers and Fig. X1.3 on Comparator for Temperature
Range from−160 to−75 °C (−256 to−103 °F).
8. Reference Temperature Unit
10.4 For testing in the range of−80 to+5 °C (−110 to+40
8.1 The reference temperature unit shall maintain the tem-
°F), use an apparatus as depicted in Test Method E77,
perature of the reference junctions within 1 °C (2 °F) of the
Appendix X1, on Discussion of Apparatus for Verification of
assumed value of reference temperature. The reference tem-
Liquid-in-Glass Thermometers and Fig. X1.4 on Comparator
perature unit shall be designed so that the temperatures of all
for Temperature Range from−80 to+5 °C (−112 to+41 °F),
the reference junctions will be isothermal.
using dry ice and a suitable liquid.
8.2 The preferred reference temperature value is 0 °C (32
10.5 For testing in the range of room temperature to 95 °C
°F). This value is the common reference temperature value for
(200°F),aheatedba
...
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