1、Designation: E601 15Standard Guide forMeasuring Electromotive Force (emf) Stability of Base-MetalThermoelement Materials with Time in Air1This standard is issued under the fixed designation E601; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、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 guide provides a method for measuring the emfstability of base-metal thermoelement mater
3、ials in air refer-enced to platinum at specified constant elevated temperaturesusing dual, simultaneous, emf indicators, or using a single emfindicator, with the test and reference emf measured alternately.This test is conducted over a period of weeks.1.2 A calibrated platinum-rhodium/platinum therm
4、ocoupleis 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 the stability of individual thermoelements. Byc
5、ombining 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 platinum leg of the platinum-rhodium/platinumreference
6、 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 electricalresistance between joined thermoelements, as me
7、asured at the referencejunctions.NOTE 2See ASTM MNL 12 for recommended upper temperaturelimits in air.2NOTE 3This guide is only applicable for initially new thermoele-ments. Base-metal thermoelements exposed to temperatures above 200Cbecome thermoelectrically inhomogeneous, and stability testing of
8、inho-mogeneous 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 and health practices and determine the applica-bil
9、ity of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E220 Test Method for Calibration of Thermocouples ByComparison TechniquesE230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE344 Terminology Relating to Thermometry and
10、 Hydrom-etryE563 Practice for Preparation and Use of an Ice-Point Bathas a Reference TemperatureE1159 Specification for Thermocouple Materials, Platinum-Rhodium Alloys, and Platinum2.2 Other Referenced DocumentsNIST Monograph 1753. Terminology3.1 DefinitionsThe definitions given in Terminology E344s
11、hall apply to this guide.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 thermocouple juncti
12、ons heldat fixed temperatures and with the thermal profile along thethermoelements held constant.3.2.3 half-maximum heated length, nthe distance betweenthe tip of the temperature sensor and the position along thelength of the sensor leads or sheath where the temperatureequals the average of the cali
13、bration-point and ambient tem-peratures.3.2.4 gradient zone, nthe section of a thermocouple that isexposed during a measurement to temperatures in the rangefrom tamb+ 0.1(tm tamb)totamb+ 0.9(tm tamb), where tambis ambient temperature and tmis the temperature of themeasuring junction.1This guide is u
14、nder the jurisdiction of ASTM Committee E20 on TemperatureMeasurement and is the direct responsibility of Subcommittee E20.04 on Thermo-couples.Current edition approved May 1, 2015. Published June 2015. Originallyapproved in 1977. Last previous edition approved in 2013 as E601 07a (2013).DOI: 10.152
15、0/E0601-15.2Manual 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, orcontact ASTM Customer Service at service
16、astm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.5 reference thermocouple, ncalibrated Type S or TypeR t
17、hermocouple.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 to a common reference temperature.4. Summa
18、ry of Test4.1 In this test, the emf of a test thermocouple, comprised ofa base-metal thermoelement relative to a platinum referencethermoelement, is determined as a function of time for aspecified test temperature and thermal profile. If care is takento maintain the chemical purity and annealed meta
19、llurgicalstate of the platinum thermoelement, the platinum will bethermoelectrically 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) is used tomeasure the test temperature, and the emf (Etest
20、) of the testthermocouple is measured either simultaneously or alternatelywith Eref. The test consists of the measurement of Etestatspecified time intervals and at a specified constant value of Erefwhich corresponds to a specified, constant temperature, untilthe required time of the test is exceeded
21、 or until an open circuitin the base-metal thermoelement results.4.2 This test is based on Method A of Test Method E220,where the reference thermocouple of Test Method E220becomes the reference thermocouple used to measure the testtemperature and one specified constant temperature replacesthe series
22、 of measured temperatures of Test Method E220.5. Significance and Use5.1 This test is important because the accuracy of a tem-perature measurement by a thermocouple is directly related tothe emf stability of the thermoelements.5.2 This test is used to verify that the tested thermoelementsmeet the in
23、tended requirements.5.3 This test is useful in comparing the emf stability of twobase metal thermoelements under the same conditions. The testand reference emf may be measured either simultaneously oralternately.5.4 The relative stabilities of base metal thermoelementsdetermined by this test are val
24、id only under the specified testconditions. Results will be affected by changes in any of thefollowing conditions: (1) temperature profile or gradient alongthe length of the thermoelements; (2) abundance, velocity andcomposition of the air surrounding the test pieces; (3) thermo-electric inhomogenei
25、ty of the test thermoelements; (4) stabilityof the platinum thermoelement.5.5 The test does not address the determination of basemetal thermoelement stabilities over a series of temperaturechanges.5.6 The reliability of this test depends on the emf stability ofthe reference platinum thermoelement. F
26、or testing the relativeemf stability of base-metal thermoelements, a reference ele-ment of platinum that has sufficient thermoelectric stability todetermine any significant change in emf of base-metal thermo-elements shall be used. To ascertain that the experimentalmethod protects the platinum suffi
27、ciently from degradation, themethod shall be validated by performing the procedure de-scribed in Appendix X1 prior to the actual test.5.7 The test result does not apply to applications in whichthe temperature distribution, for a given measuring junctiontemperature, changes with time.6. Apparatus6.1
28、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. The referencethermocouple shall consist of either standard tolerance orspecial tolerance wire as per Table 1
29、in Specification E230. Thechoice of tolerance will not affect the determination of ther-moelement drift. This thermocouple shall be of sufficientlength to minimize the effect of heat conduction along thelengths of the wires upon the measuring junction temperature.(Note: platinum is a better heat con
30、ductor than most base metalthermocouple wires.) The length shall be sufficient to enablethe reference thermocouples measuring junction to be locatedwithin the test furnaces zone of nearly uniform temperature(refer to 6.5.2).6.2 Platinum Reference ThermoelementThe emf of thetest thermoelements shall
31、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. The lengthof this wire shall exceed that of the test specimen to minimizethe transfer of heat from the meas
32、uring junction to thereference junction during testing (see 6.3). For more informa-tion concerning a platinum reference thermoelement, Specifi-cation E1159 may be consulted.6.3 Test SpecimensThe test specimens shall be lengths ofwires, rods, ribbons, or strips of the coils or spools of thebase-metal
33、 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 shall be at least 0.8 m (30 in.) depending onthe length of the testing medium and the transverse sizes of th
34、ethermoelements. 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 Reference Junction TemperatureThe reference junc-tion ends of the test specimens, of the platinum referenceele
35、ment, if used, and of the reference thermocouple shall bemaintained at a known constant temperature during a measure-ment cycle. The uncertainty attributable to the referencejunction temperature shall be less than 60.1C. Ice pointreference junction baths provide a relatively simple and reli-able mea
36、ns for maintaining the reference junction at 0C(32F) when proper precautions are exercised in their use.Practice E563 provides an acceptable method for utilizing theice point as a reference junction bath. Subsection 7.3 of TestE601 152Method E220 may be consulted for alternative methods ofproviding
37、a reference junction temperature.6.5 Tube FurnaceThe test shall be conducted in an elec-trically heated tube furnace such as described in subsection7.2.3 of E220. The furnace tube shall be long enough to permita depth of immersion of the thermocouple measuring junctionsthat is sufficient to assure t
38、hat the temperature of the measuringjunctions is not affected by heat conduction along the thermo-elements.6.5.1 Means shall be provided to control the temperature ofthe furnace to within 610C (618F) of a nominal tempera-ture during the performance of the test.6.5.2 The test shall be conducted in a
39、uniformly heatedfurnace providing a nearly isothermal work zone sufficientlylarge to maintain all junctions at the same temperature.6.5.3 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 vi
40、cinity of thework zone, using a platinum-rhodium alloy thermocouple or aplatinum resistance thermometer prior to commencement ofthe test. 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 fixe
41、d half-maximumheated length, and to move a second thermometer along thefurnace-tube axis. Adjust the readings of the moveable ther-mometer by adding the correction (tfixed(time) tfixed(initial),where tfixedis the temperature indication of the thermometer atfixed half-maximum heated length.6.5.3.1 A
42、thermoelement extending from ambient tempera-ture into an isothermal zone of a furnace will come toequilibrium with the temperature of the isothermal zonethrough radiative, convective, and conductive heat transferbetween the thermoelement and the surrounding furnace envi-ronment. The distance of imm
43、ersion, Leq, into the isothermalzone needed to achieve thermal equilibrium depends signifi-cantly on both the thermoelement diameter and its thermalconductivity. The characteristic length for a wire to achievethermal equilibrium with its surroundings is given by theapproximate correlation:Leq5 2.5 c
44、m!Sd1mmD1/2Sk100 W/mK!D1/2(1)where:k = the thermal conductivity of the thermoelement, andd = the diameter of the thermoelement.Calculate the distance Leqfor each tested thermoelement inunits of W/(m K), and d is the diameter of the thermoelementin millimeters. The equivalent equation in English unit
45、s, with din units of inches and k in units of BTU/(hrftF) is:Leq5 1in!Sd0.04 inD1/2Sk58 BTU/hr.ftF!D1/2(2)Calculate the distance Leqfor each tested thermoelement andthe platinum reference thermoelement. The approximate ther-mal conductivities listed in Table 1 may be used for this pur-pose. Measure
46、the diameter dmjof the measuring junctionassembly (see 7.1). Identify the maximum Lmaxof the set ofall calculated Leqvalues and dmj.NOTE 4Eq 1 was derived for a temperature of 200C, which is nearthe lower limit of observable thermoelement drift. For highertemperatures, the value of Leqfrom Eq 1 will
47、 give an upper limit on theactual equilibration length.6.5.3.2 The standard uncertainty due to thermal non-uniformity is the maximum temperature variation in the profilefrom subsection 6.5.3 between the measuring junction locationand a distance Lmaxaway from the measuring junction.6.5.3.3 Alternativ
48、e methods 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 Electrom
49、otive Force IndicatorThe emf-measuring in-strumentation 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. Subsections 6.2 and 7.4 of Test Method E220 maybe consulted for further discussions of thermal emf indicatorsand methods of emf measurement.6.7 Connecting WiresConnecting wires from the referencejunctions to the emf indicator or indicators shall be electricallyinsulated copper. If the test is sensitive to electrost
