ASTM E601-2007e1 Standard Test Method for Measuring Electromotive Force (emf) Stability of Base-Metal Thermoelement Materials with Time in Air.pdf

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1、Designation: E 601 07e1Standard Test Method forMeasuring Electromotive Force (emf) Stability of Base-MetalThermoelement Materials with Time in Air1This standard is issued under the fixed designation E 601; the number immediately following the designation indicates the year oforiginal adoption or, in

2、 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.e1NOTEEditorial changes were made throughout in July 2007.1. Scope1.1 This test method measure

3、s emf stability of base-metalthermoelement materials in air referenced to platinum atspecified constant elevated temperatures using dual, simulta-neous, emf indicators, or using a single emf indicator, with thetest and reference emf measured alternately. This test isconducted over a period of weeks.

4、1.2 A calibrated platinum-rhodium/platinum thermocoupleis used as a reference standard to establish the test temperature.1.3 The useful life of a thermocouple depends on thestability of the emf generated at given temperatures for arequired time interval. This method provides a quantitativemeasure of

5、 the stability of individual thermoelements. Bycombining the results of the positive (P) and negative (N)thermoelements, the stability of a thermocouple comprised ofboth P and N thermoelements may be obtained. The emf of anindividual thermoelement is measured against platinum, whichmay be the platin

6、um leg of the platinum-rhodium/platinumreference thermocouple, or an additional platinum reference.NOTE 1Some thermoelements may show insignificant emf drift whileundergoing relatively rapid oxidation. In these cases, failure of thethermoelement may be indicated only by a large rise in the electrica

7、lresistance of the thermocouple, as measured between the referencejunctions.NOTE 2See ASTM MNL 12 for recommended upper temperaturelimits in air.2NOTE 3This test method is only applicable for initially new thermo-elements. Base-metal thermoelements exposed to temperatures above 200C become thermoele

8、ctrically inhomogeneous, and stability testing ofinhomogeneous thermoelements will give ambiguous results.1.4 This standard 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 an

9、d health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E 220 Test Method for Calibration of Thermocouples ByComparison TechniquesE 230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized Thermoc

10、ouplesE 344 Terminology Relating to Thermometry and Hydrom-etryE 563 Practice for Preparation and Use of an Ice-Point Bathas a Reference TemperatureE 1159 Specification for Thermocouple Materials,Platinum-Rhodium Alloys, and Platinum3. Terminology3.1 DefinitionsThe definitions given in TerminologyE

11、344 shall apply to this test method.3.2 Definitions of Terms Specific to This Standard:3.2.1 emf indicator, nan instrument that measures the emfand displays the value, for example, a digital voltmeter(DVM).3.2.2 emf stability, nchange in emf (or in equivalenttemperature) with time, with the thermoco

12、uple junctions heldat fixed temperatures and with the thermal profile along thethermoelements held constant.3.2.3 immersion depth, nthe distance between the tip ofthe temperature sensor and the position along the length of thesensor leads or sheath where the temperature equals theaverage of the cali

13、bration-point and ambient temperatures.3.2.4 gradient zone, nthe section of a thermocouple that isexposed during a measurement to temperatures in the rangefrom tamb+ 0.1(tmtamb)totamb+ 0.9(tmtamb), where tambis ambient temperature and tmis the temperature of themeasuring junction.1This test method i

14、s under the jurisdiction of ASTM Committee E20 onTemperature Measurement and is the direct responsibility of Subcommittee E20.04on Thermocouples.Current edition approved May 1, 2007. Published June 2007. Originallyapproved in 1977. Last previous edition approved in 1997 as E 601 81 (1997)which was w

15、ithdrawn in January 2006 and reinstated in May 2007.2Manual on the Use of Thermocouples in Temperature Measurement: FourthEdition, Available from ASTM Headquarters, 100 Barr Harbor Drive, WestConshohocken, PA 19428, www.astm.org.3For referenced ASTM standards, visit the ASTM website, www.astm.org, o

16、rcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.5 reference t

17、hermocouple, ncalibrated Type S or TypeR thermocouple.3.2.6 test thermocouple, nthermocouple composed of thethermoelement being tested and the platinum reference ther-moelement.3.2.7 normalize, vto mathematically adjust experimentalemf data acquired at a set of temperatures to values corre-sponding

18、to a common reference temperature.4. Summary of Test Method4.1 In this test method, the emf of a test thermocouple,comprised of a base-metal thermoelement relative to a plati-num reference thermoelement, is determined as a function oftime for a specified test temperature and thermal profile. If care

19、is taken to maintain the chemical purity and annealed metal-lurgical state of the platinum thermoelement, the platinum willbe thermoelectrically stable. In that case, variation in this emfvalue is attributed to instability of the base-metal thermoele-ment. The emf of the reference thermocouple (Eref

20、) is used tomeasure the test temperature, and the emf (Etest) of the testthermocouple is measured either simultaneously or alternatelywith Eref. The test method consists of the measurement of Etestat specified time intervals and at a specified constant value ofErefwhich corresponds to a specified, c

21、onstant temperature,until the required time of the test is exceeded or until an opencircuit in the base-metal thermoelement results.4.2 This test method is based on Method A of Test MethodE 220, where the reference thermocouple of Test Method E 220becomes the reference thermocouple used to measure t

22、he testtemperature and one specified constant temperature replacesthe series of measured temperatures of Test Method E 220.5. Significance and Use5.1 This test method is important because the accuracy of atemperature measurement by a thermocouple is directly relatedto the emf stability of the thermo

23、elements.5.2 This test method is used to verify that the testedthermoelements meet the intended requirements.5.3 This test method is useful in comparing the emf stabilityof two base metal thermoelements under the same conditions.The test and reference emf may be measured either simulta-neously or al

24、ternately.5.4 The relative stabilities of base metal thermoelementsdetermined by this test method are valid only under thespecified test conditions. Results would be affected by changesin the following conditions: (1) temperature profile or gradientalong the length of the thermoelements; (2) abundan

25、ce, veloc-ity and composition of the air surrounding the test pieces; (3)thermoelectric inhomogeneity of the test thermoelements; (4)stability of the platinum thermoelement.5.5 The test method does not address the determination ofbase metal thermoelement stabilities over a series of tempera-ture cha

26、nges.5.6 The reliability of this test method depends on the emfstability of the reference platinum thermoelement. For testingthe relative emf stability of base-metal thermoelements, areference element of platinum that has sufficient thermoelectricstability to determine any significant change in emf

27、of base-metal thermoelements shall be used. To ascertain that theexperimental method protects the platinum sufficiently fromdegradation, the method shall be validated by performing theprocedure described in Appendix X1 prior to the actual test.5.7 The test result does not apply to applications in wh

28、ichthe temperature distribution, for a given measuring junctiontemperature, changes with time.6. Apparatus6.1 Thermocouple Used to Measure the TestTemperatureA reference Type S or Type R thermocouplewith 0.50 mm diameter (24 AWG) thermoelements or largershall be used to measure the test temperature.

29、 The referencethermocouple shall consist of either standard tolerance orspecial tolerance wire as per Table 1 in Specification E 230.The choice of tolerance will not affect the determination ofthermoelement drift. This thermocouple shall be of sufficientlength to minimize the effect of heat conducti

30、on along thelengths of the wires upon the measuring junction temperature.(Note: platinum is a better heat conductor than most base metalthermocouple wires.) Length shall be sufficient to enable thereference thermocouples measuring junction to be locatedwithin the test furnaces zone of nearly uniform

31、 temperature(refer to 6.5.2).6.2 Platinum Reference ThermoelementThe emf of thetest thermoelements shall be measured relative to a 0.50 mmdiameter (24 AWG) platinum wire. This wire may be theplatinum wire of the Type S or R reference thermocouple or asecond 0.50 mm diameter (24AWG) platinum wire. Th

32、e lengthof this wire shall exceed that of the test specimen to minimizethe transfer of heat from the measuring junction to thereference junction during testing (see 6.3). For more informa-tion concerning a platinum reference thermoelement, Specifi-cation E 1159 may be consulted.6.3 Test SpecimensThe

33、 test specimens shall be lengths ofwires, rods, ribbons, or strips of the coils or spools of thebase-metal thermoelements to be evaluated. Their lengths shallbe adequate to minimize the transfer of heat from the measur-ing junctions to the reference junctions during the period oftest. The lengths sh

34、all be at least 0.8 m (30 in.) depending onthe length of the testing medium and the transverse sizes of thethermoelements. The specimens shall be free of kinks or otherdefects due to mechanical deformation, and shall be continuouswithout splices between the measuring and reference junctions.6.4 Refe

35、rence Junction TemperatureThe reference junc-tion ends of the test specimens, of the platinum referenceelement, if used, and of the reference thermocouple must bemaintained at a known constant temperature during a measure-ment cycle. The uncertainty attributable to the referencejunction temperature

36、shall be less than 60.1 C. Ice pointreference junction baths provide a relatively simple and reli-able means for maintaining the reference junction at 0 C (32F) when proper precautions are exercised in their use. PracticeE 563 provides an acceptable method for utilizing the ice pointas a reference j

37、unction bath. Section 7.3 of Test Method E 220may be consulted for alternative methods of providing areference junction temperature.6.5 Tube FurnaceThe test shall be conducted in anelectrically heated tube furnace such as described in Section7.2.3 of E 220. The furnace employed shall have the follow

38、ingE60107e12capabilities: The furnace tube shall be long enough to permit adepth of immersion of the thermocouple measuring junctionsthat is sufficient to assure that the temperature of the measuringjunctions is not affected by heat conduction along the thermo-elements.6.5.1 Means shall be provided

39、to control the temperature ofthe furnace to within 610 C (618 F) of a nominal tempera-ture during the performance of the test.6.5.2 The test shall be conducted in a uniformly heatedfurnace providing a nearly isothermal work zone sufficientlylarge to maintain all junctions at the same temperature.6.5

40、.3 To determine the uncertainty resulting from tempera-ture non-uniformities in the work zone, measure the tempera-ture profile along the thermocouple axis in the vicinity of thework zone, using a platinum-rhodium alloy thermocouple or aplatinum resistance thermometer prior to commencement ofthe tes

41、t. If the furnace temperature is not sufficiently stable toobtain a temperature profile with a single thermometer, it maybe useful to place one thermometer at a fixed immersion depth,and to move a second thermometer along the furnace-tube axis.Adjust the readings of the moveable thermometer by addin

42、gthe correction (tfixed(time) tfixed(initial), where tfixedis thetemperature indication of the thermometer at fixed immersiondepth.6.5.3.1 The characteristic length for a wire to achievethermal equilibrium with its surroundings is given by theapproximate correlation:Leq5 2.5 cm!Sd1mmD1/2Sk100 W/mK!D

43、1/2(1)where k is the thermal conductivity of the thermoelement, andd is the diameter of the thermoelement. Calculate the distanceLeqfor each tested thermoelement and the platinum referencethermoelement. The approximate thermal conductivities listedin Table 1 may be used for this purpose. Measure the

44、 diameterdmjof the measuring junction assembly (see 7.1). Identify themaximum Lmaxof the set of all calculated Leqvalues and dmj.NOTE 4Eq 1 was derived for a temperature of 200 C, which is nearthe lower limit of observable thermoelement drift. For higher tempera-tures, the value of Leqfrom Eq 1 will

45、 give an upper limit on the actualequilibration length.6.5.3.2 The standard uncertainty due to thermal non-uniformity is the maximum temperature variation in the profilefrom Section 6.5.3 between the measuring junction locationand a distance Lmaxaway from the measuring junction.6.5.3.3 Alternative m

46、ethods may be used to determine thestandard uncertainty due to thermal non-uniformity, such ascomparison of results in the test furnace with results obtainedeither in fixed-point cells or in a stirred liquid bath of hightemperature uniformity; or numerical heat-transfer calcula-tions.6.6 Electromoti

47、ve Force IndicatorThe emf measuringinstrumentation shall have a measurement uncertainty of notmore than 1 V at 1 000 V and 12 V at 50 000 V for thistest. The emf indicators may be potentiometers or digitalvoltmeters. Sections 6.2 and 7.4 of Test Method E 220 may beconsulted for further discussions o

48、f thermal emf indicators andmethods of emf measurement.6.7 Connecting WiresConnecting wires from the refer-ence junctions to the emf indicator or indicators shall beelectrically insulated copper. If the test is sensitive to electro-static interference, the wires shall be electrically shielded. Ifele

49、ctromagnetic interference is present, the conductors shall betwisted to minimize this effect.6.8 Selector SwitchesWhen more than one thermoelementis to be tested, a selector switch is introduced into the copperpart of the circuit between the reference junctions and thethermal-emf indicators. These switches shall comply with 7.5.1of Test Method E 220.6.9 Thermocouple InsulationFor the segment of the ther-moelements exposed to temperatures above ambient, ceramictubing may be used to support and electrically insulate the testthermoelement, the