1、Designation: E 207 08Standard 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a test for determining thethe
3、rmoelectric 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 app
4、licable to new thermocouple materialsover the 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 thermoc
5、ouples. 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
6、does 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 S
7、tandards:3E77 Test Method for Inspection and Verification of Ther-mometersE 220 Test Method for Calibration of Thermocouples ByComparison TechniquesE 230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE 344 Terminology Relating to Thermometry and Hydrom-e
8、tryE 563 Practice for Preparation and Use of an Ice-Point Bathas a Reference Temperature3. 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 phy
9、sical 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 in
10、dicated 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 s
11、ingle 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.1This test method is under the jurisdiction o
12、f ASTM Committee E20 onTemperature Measurement and is the direct responsibility of Subcommittee E20.04on Thermocouples.Current edition approved May 1, 2008. Published June 2008. Originallyapproved in 1962 . Last previous edition approved in 2000 as E 20700.2Manual on the Use of Thermocouples in Temp
13、erature Measurement, ASTMMNL-12, Fourth Edition, ASTM, April 1993. (Revision of STP 407B).3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Sum
14、mary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.4 The emf of the test thermoelement relative to Pt-67 isdetermined by algebraically adding the measured emf to theemf of the reference thermoelement at ea
15、ch 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 initial values of emf because the timeat the test temperature is limited.5.2 This test method is employed mainly b
16、y 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 to matchto companion thermoelements for use as thermocouples or inextension wiring.5.3 The emf of a thermocouple
17、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. The emf of a thermocouple may alsobe determined by the test described i
18、n 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 their production or distribution,not for the accurate determination o
19、f 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 in the wires because of a chemicalor metallurgical reaction while in s
20、ervice. 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 test results are suitable for specification acceptance,manufacturing c
21、ontrol, 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 spool or coil. Theextreme ends shall not be acceptable if they are distor
22、ted 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 shall be cleaned of any extraneoussurface contamination.6.4 The specim
23、ens 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 depth of immersion in the testing medium and thetransverse size (for
24、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 reference thermoelement has its emf establishedrelative to NIST Pt-67 o
25、ver 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 Specification E 230 within onehalf the standard tolerance specified for t
26、he 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 so that oxidation caused by the tempera-tures of testing would not si
27、gnificantly 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, it shall be manufactured in onecontinuous length with no in-process welds. . Cold working ofthe material after the final anneal shall be minimized7.4.1 A specim
28、en 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 than 260 C (500 F) apart.7.4.2 The emf difference between the specimens of 7.4.1 ateach test temperatu
29、re 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 the stated uniformity require-ments, at least one unused 1-m (3-ft) section shall be certifiedby a refe
30、rence 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) or atintervals that do not exceed 25 % of the test temperature range,whichever is the lesser. If fewer
31、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 reference thermoelement at intermedi-ate values of temperature may be determined by one of thefollowing
32、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 referencethermoelement emf from the function value is first calculated atthe test temperature values.At an intermediate t
33、emperature, 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 theintermediate temperature. For the least squares method, thenumber of data points shall equal or exceed
34、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 intermediatetemperature.E2070827.5.2.2 For the thermoelements for which there is no emffunction for that thermoelement
35、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 datapoints shall equal or exceed twice the number of parametersfitted. Evaluation of the polynomial at the
36、 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, asubcomponent of uncertainty shall be added to the uncertaintybudget equal to:u 51Ndf(iEi Efit!2# (
37、1)where: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, andNdf= the number of degrees of freedom in the fit =number of data points number of fitted parameters.7.5
38、.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 account for the interpolation error. This uncer-tainty component may be estimated by calculating the erro
39、r 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 combined.7.6 The segment of reference thermoelement that is used foreach test shall be unaffected by a prio
40、r 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 effects ofstrain, the remainder may be reused. For noble metals and theiralloys, the number of reuses d
41、epends 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 segmentthat was not subjected to routine use.8. Reference Temperature Unit8.1 The reference temperatur
42、e unit shall maintain the tem-perature of the reference junctions within 5 C (9 F) of theassumed value of reference temperature. The reference tem-perature unit shall be designed so that the temperatures of allthe reference junctions will be isothermal.NOTE 1The preferred reference junction temperat
43、ure is 0 C (32 F).This may be approximated with an ice bath (see Practice E 563),“automatic ice point” unit or a “zone box” (see MNL-12). Care should beexercised to maintain the reference junction temperatures for both thereference and test thermocouples at the same temperature.9. Measuring Junction
44、9.1 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 preferred method ofjoining, particularly for test temperatures above 260 C (500F).9.2 The number of test specimens that may be tested at onet
45、ime 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 isothermal conditionsat the measuring or reference junction.10. Test Temperature Medium10.1 Normally, both the test and reference thermoelem
46、entshave the same nominal composition and consequently haveapproximately the same values of Seebeck coefficients. There-fore, the measured emf is expected to be small in magnitude(compared to the emf relative to Pt-67) and vary only slightlyas a function of temperature. Therefore, it is not necessar
47、y 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 thedevic
48、es and precautions in Test Method E77,Appendix X1, onDiscussion of Apparatus for Verification of Liquid-in-GlassThermometers and Fig. X1.3 on Comparator for TemperatureRange from 160 to 75 C (256 to 103 F).10.4 For testing in the range of 80 to +5 C (110 to +40F), use an apparatus as depicted in Tes
49、t Method E77,Appendix X1, on Discussion of Apparatus for Verification ofLiquid-in-Glass Thermometers and Fig. X1.4 on Comparatorfor Temperature Range from 80 to +5 C (112 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), a heated bath using demineralized water may be used.10.6 In the range of 5 to 300 C (40 to 600 F), a stirred bathof an oil with a flash point higher than the test temperature maybe used. Refer to Test Method E77, Appendix X1, onDiscussion of Apparatus for
