1、Designation: E 207 00Standard Test Method forThermal EMF Test of Single Thermoelement Materials byComparison with a Reference Thermoelement of SimilarEMF-Temperature Properties1This standard is issued under the fixed designation E 207; the number immediately following the designation indicates the y
2、ear oforiginal adoption or, in the case 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 a test for determining theth
3、ermoelectric emf of a thermoelement versus NIST platinum67 (Pt-67) by means of measuring the difference between theemf of the test thermoelement and the emf of a referencethermoelement (previously referred to as a secondary stan-dard), which has a known relationship to NIST Pt-67.1.2 This test is ap
4、plicable to thermocouple materials overthe temperature ranges normally associated with thermo-couples and their extension wires. The table on SuggestedUpper Temperature Limits for Protected Thermocouples inSpecification E 230 lists the ranges associated with the letter-designated types of thermocoup
5、les. ASTM MNL-122lists thetemperature range of extension circuit materials.1.3 This test is not applicable to stability testing or inhomo-geneity testing.1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.5 This standard doe
6、s not purport to address all of thesafety concerns, if any, associated 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 Stan
7、dards:E 77 Test Method for Inspection and Verification of Ther-mometers3E 220 Test Method for Calibration of Thermocouples byComparison Techniques3E 230 Specification for Temperature-Electromotive Force(EMF) Tables for Standardized Thermocouples3E 344 Terminology Relating to Thermometry and Hydrom-e
8、try3E 563 Practice for Preparation and Use of an Ice-Point Bathas a Reference Temperature33. Terminology3.1 DefinitionsThe terms used in this test method aredefined in Terminology E 344.3.2 Definitions of Terms Specific to This Standard:3.2.1 reference facility, nNIST, or a testing laboratorywhose p
9、hysical standards are traceable to NIST or anothernational standards laboratory.3.2.2 test temperature, nthe temperature of the measuringjunction.3.2.2.1 DiscussionIn reporting the results, the value of thetest temperature may be rounded off, provided the stated testtemperature is within the bounds
10、indicated in 10.10.4. Summary of Test Method4.1 The emf of a thermoelement sample is determined bycomparison to a reference thermoelement that has similarSeebeck coefficients.4.2 This test is conducted on one or more lengths ofspecimens connected to a single length of the referencethermoelement at a
11、 single point. The joined ends are held at thetest temperature, and their opposite ends are held at a constantreference temperature.4.3 The emf of the reference thermoelement relative toPt-67 at several test temperatures are provided by a referencefacility.4.4 The emf of the test thermoelement relat
12、ive to Pt-67 isdetermined by algebraically adding the measured emf to theemf of the reference thermoelement at each test temperature.5. Significance and Use5.1 This test method is designed to calibrate a thermoele-ment at one or more test temperatures. The data obtained aresometimes referred to as i
13、nitial values of emf because the timeat the test temperature is limited.5.2 This test method is employed mainly by providers ofspools or coils of wire or strip of thermoelectric material.Generally more than one specimen at a time is tested, and theresultant emf of individual thermoelements are used
14、to matchto companion thermoelements for use as thermocouples or inextension wiring.1This 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 Aug. 10, 2000. Published Sep
15、tember 2000. Originallypublished as E 20762 T. Last previous edition E 20796.2Manual on the Use of Thermocouples in Temperature Measurement, ASTMMNL-12, Fourth Edition, ASTM, April 1993. (Revision of STP 407B).3Annual Book of ASTM Standards, Vol 14.03.1Copyright ASTM, 100 Barr Harbor Drive, West Con
16、shohocken, PA 19428-2959, United States.5.3 The emf of a thermocouple comprised of two differentthermoelements as tested with this test method may be deter-mined by algebraically subtracting the emf of the negativethermoelement from the emf of the positive thermoelement ata particular temperature. T
17、he emf of a thermocouple may alsobe determined by the test described in Test Method E 220, butTest Method E 220 does not take into account the values of theemf of the individual thermoelements relative to Pt-67.5.4 This test method is normally used for the calibration ofthermocouple materials during
18、 their production or distribution,not for the accurate determination of the properties of a usedthermocouple. If the test samples were subjected to previoususe, the test results may not reflect the same emf as thethermocouple did while in service. For example, inhomogene-ities may have been induced
19、in the wires because of a chemicalor metallurgical reaction while in service. Since emf is devel-oped in the thermal gradient, and it is unlikely that thetemperature profile along the wire under testing conditions willbe the same as it was while in service, the test results may bemisleading.5.5 The
20、test results are suitable for specification acceptance,manufacturing control, design, or research and developmentpurposes.6. Test Specimen6.1 Each sample shall represent one continuous spool or coilof thermoelectric material. The sample shall consist of twospecimens, one cut from each end of the spo
21、ol or coil. Theextreme ends shall not be acceptable if they are distorted orhave been subjected to processing dissimilar to the bulk of thespool or coil.6.2 Insulation or covering shall be removed with care if itinterferes with the test. Straining the test specimen shall beavoided.6.3 The specimens
22、shall be cleaned of any extraneoussurface contamination.6.4 The specimens and the reference thermoelement shall belong enough to extend continuously from the measuringjunction to the reference junction. A length of 600 to 1200 mm(2 to 4 ft) is generally satisfactory. The exact length dependsupon the
23、 depth of immersion in the testing medium and thetransverse size (for example, diameter of round wire, width ofstrip) of the thermoelement.6.4.1 Heating of the measuring junctions shall not affect thetemperature of the reference junctions during the period of test.7. Reference Thermoelement7.1 The r
24、eference thermoelement has its emf establishedrelative to NIST Pt-67 over the temperature range of itsintended use. A specific lot of thermoelement material isusually reserved for use as reference thermoelements.7.2 The emf of the reference thermoelement versus plati-num (Pt-67) shall conform to Spe
25、cification E 230 within onehalf the standard tolerance specified for the related thermo-couple type. For example, the tolerance for KP versus Pt-67 is6 1Cor6 0.375% of temperature from 0 C to 1260 C,whichever is greater.7.3 The cross section of the base metal thermoelement shallbe sufficiently large
26、 so that oxidation caused by the tempera-tures of testing would not significantly affect its emf over theperiod of the test.7.4 To provide some assurance that the reserved lot isuniform in emf from end to end, that lot shall be taken from asingle source (ingot), shall be manufactured in one continuo
27、uslength with no in-process welds, and efforts made to minimizecold working the material.7.4.1 A specimen from each end of the reserved lot shall betested using this test method. The test temperatures shallinclude the extremes of the intended range of use and addi-tional test points that are no more
28、 than 260 C (500 F) apart.7.4.2 The emf difference between the specimens of 7.4.1 ateach test temperature shall not exceed the equivalent of 0.33 C(0.6 F) for that thermocouple type or 0.05 % of the value ofthe test temperature in degrees Celsius, whichever is thegreater.7.5 From the lot that meets
29、the stated uniformity require-ments, at least one unused 1-m (3-ft) section shall be certifiedby a reference facility to document its emf relative to Pt-67.Traceability shall be required in the form of a certificate issuedby the reference facility.7.5.1 Emf data shall be provided every 50 C (100 F)
30、or atintervals that do not exceed 25 % of the test temperature range,whichever is the lesser. If fewer than the aforementionednumber of points are taken, then the data are applicable only ator near the measured temperatures, and interpolation beyondthem should not be attempted.7.5.2 The emf of the r
31、eference thermoelement at intermedi-ate values of temperature may be determined by one of thefollowing methods.7.5.2.1 For the letter-designated thermocouple types, emffunctions for thermoelements versus Pt-67 are given in Speci-fication E 230. In these cases, the deviation of the referencethermoele
32、ment emf from the function value is first calculated atthe test temperature values. At an intermediate temperature, thedeviation of emf is calculated either by linear interpolation orby fitting a polynomial to the deviation of emf using themethod of least squares, and evaluating the polynomial at th
33、eintermediate temperature. For the least squares method, thenumber of data points shall equal or exceed twice the numberof parameters fitted. Addition of the deviation of emf to thefunction value at the intermediate temperature gives the emfvalue of the reference thermoelement at the intermediatetem
34、perature.7.5.2.2 For the thermoelements for which there is no emffunction for that thermoelement versus Pt-67, a function maybe determined by fitting a polynomial to the emf valuesreported by NIST for the reference thermoelement versusPt-67, using the method of least squares. The number of datapoint
35、s shall equal or exceed twice the number of parametersfitted. Evaluation of the polynomial at the intermediate tem-perature gives the emf of the reference thermoelement. In caseswhere the deviations of the fitted data from the polynomial aresignificant compared to other uncertainties in the test, as
36、ubcomponent of uncertainty shall be added to the uncertaintybudget equal to:u 51Ndf(iEi Efit!2# (1)E 2072where:u = uncertainty,Ei= the emf at the ith calibration temperature value ofthe reference thermoelement that has been calibratedrelative to NIST Pt-67,Efit= the emf of the fitted polynomial, and
37、Ndf= the number of degrees of freedom in the fit =number of data points number of fitted parameters.7.5.2.3 Linear interpolation of the reference thermoelementemf, rather than the deviation of emf, may also be done, but useof this method requires inclusion of an additional uncertaintycomponent to ac
38、count for the interpolation error. This uncer-tainty component may be estimated by calculating the error oflinear interpolation of the emf values obtained from the emffunctions for thermoelements versus Pt-67 in SpecificationE 230 or another source. This error may be as large as all othererrors comb
39、ined.7.6 The segment of reference thermoelement that is used foreach test shall be unaffected by a prior test. For example, anysegment of KP, EP, or JP thermoelement, exposed to tempera-tures exceeding 260 C (500 F) shall not be reused. However,if it shows no evidence of its test environment and no
40、effects ofstrain, the remainder may be reused. For noble metals and theiralloys, the number of reuses depends upon the amount of strainor contamination of the segment. Noble metal referencethermoelements should be checked for emf conformity afterten uses or less against another noble metal reference
41、 segmentthat was not subjected to routine use.8. Reference Temperature Unit8.1 The reference temperature unit shall maintain the tem-perature of the reference junctions within 1 C (2 F) of theassumed value of reference temperature. The reference tem-perature unit shall be designed so that the temper
42、atures of allthe reference junctions will be isothermal.8.2 The preferred reference temperature value is 0 C (32F). This value is the common reference temperature value fortables of thermoelectric emf versus temperature, such asSpecification E 230. The physical realization of 0 C (32 F)can be closel
43、y approximated with a carefully prepared andmaintained ice bath. Refer to the guidelines for the use of anice-point bath as a reference temperature unit in Practice E 563and MNL12.8.3 The 0 C (32 F) reference temperature value can alsobe physically approximated with a water triple point cell.8.4 An
44、automatic ice point unit (such as a Peltier-effectcooler) may also be used. Refrain from using the type of unitthat has built-in extension wiring, because of wire matchingerrors.8.5 A reference temperature other than the ice point may beused during the test, such as that provided by a “zone box” ora
45、 constant temperature oven, as described in MNL12. In thatcase, the emf of the test thermoelements versus the referencethermoelement must be determined between the ice point andthe alternate reference temperature. These emf shall be alge-braically added to the respective emf obtained at the testtemp
46、eratures, in order to accurately determine their emf versusthe ice point. See Section 13 for these calculations.9. Measuring Junction9.1 The measuring junction shall consist of an electricalconnection of the test specimens to the reference thermoele-ment at one of their ends. Welding is the preferre
47、d method ofjoining, particularly for test temperatures above 260 C (500F).9.2 The number of test specimens that may be tested at onetime is limited mainly by the thermal capacity of the system.The thermal conduction along the assembly of test thermoele-ments must not be so large as to impair isother
48、mal conditionsat the measuring or reference junction.10. Test Temperature Medium10.1 Normally, both the test and reference thermoelementshave the same nominal composition and consequently haveapproximately the same values of Seebeck coefficients. There-fore, the measured emf is expected to be small
49、in magnitude(compared to the emf relative to Pt-67) and vary only slightlyas a function of temperature. Therefore, it is not necessary tocontrol the test temperature precisely.10.2 The immersion media, insulation materials, supports,and adjacent materials shall not interact with or electricallyshunt the thermoelements.10.3 For testing in the range of 160 to 75 C (250to 100 F), a liquid nitrogen bath may be used. Refer to thedevices and precautions in Test Method E 77, Appendix X1, onDiscussion of Apparatus for Verification of Liquid-in-GlassThermome
