ASTM B77-2007(2018) Standard Test Method for Thermoelectric Power of Electrical-Resistance Alloys.pdf

1、Designation: B77 07 (Reapproved 2018)Standard Test Method forThermoelectric Power of Electrical-Resistance Alloys1This standard is issued under the fixed designation B77; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of

2、last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the ther-moelectric power of a metal or alloy with respect to copperwhen

3、the temperatures of the junctions lie between 0 and100C.1.2 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not pu

4、rport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to become familiarwith all hazards including those identified in the appropriateSafety Data Sheet (SDS) for this product/material as providedby the manufacturer, to estab

5、lish appropriate safety, health,and environmental practices, and determine the applicabilityof regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for

6、 theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2B3 Specification for Soft or Annealed Copper Wire3. Terminology3.1 thermoelectric power, Q, nthe electr

7、omotive force inan electric circuit consisting of two metals when the junctionsbetween them have a difference in temperature of 1C.3.1.1 DiscussionExperimentally, it has been found thatthe thermoelectric power of two metals is not a constant butdepends on the mean temperature of the junctions. Howev

8、er,over a range of temperature from 0 to 100C it is usuallysufficient to assume that the thermoelectric power is indepen-dent of temperature so that for this range of temperature:Q 5 E/t2t!where:E = the electromotive force developed in the circuit,t = the higher temperature at one junction, C, andt

9、= the lower temperature at the other junction, C.4. Significance and Use4.1 The purpose of this method is to determine the suitabil-ity of different metals for use in resistance apparatus in whicha low thermoelectric power is desired. As most electric circuitsare largely composed of copper, the ther

10、moelectric power of aresistance metal will generally be measured against copper.5. Test Specimen5.1 The metal or alloy to be tested shall be in the form ofsheet, ribbon, or wire and the test specimen shall be of suchlength that the two ends can be readily maintained at differenttemperatures. At each

11、 end of the specimen a copper lead ofconvenient size shall be fastened. These leads shall make goodelectrical contact with the specimen, such as that obtained bywelding, brazing, or soldering. Slight impurities in the copperhave a negligible effect on the thermoelectric power.NOTE 1When necessary to

12、 specify the quality of the copper leads,reference should be made to Specification B3.6. Procedure6.1 Measurement of TemperatureAs a matter ofprecaution, the average temperature used in determining thethermoelectric power shall be approximately the same as thatto which the material will be subjected

13、 in practice, and in nocase shall the temperature difference between the two junctionsbe less than 20C. The temperature at each of two junctionsshall be measured by a device that is sufficiently accurate todetermine the temperature difference within 5 %. A convenientmethod for determining the temper

14、atures of the junctions is toimmerse each junction in separate oil baths maintained at thedesired temperatures. Baths that are stirred and the tempera-tures of which are thermostatically controlled are to be1This test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and All

15、oys and is the direct responsibility of SubcommitteeB02.10 on Thermostat Metals and Electrical Resistance Heating Materials.Current edition approved Nov. 1, 2018. Published November 2018. Originallyapproved in 1930. Last previous edition approved in 2013 as B77 07 (2013). DOI:10.1520/B0077-07R18.2Fo

16、r 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 Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700

17、, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the Wor

18、ld Trade Organization Technical Barriers to Trade (TBT) Committee.1preferred. However, beakers of oil which are supported byblocks of metal, sand baths, or other means may be used,provided the thermal capacity of these assemblies is such thatwhen the heat is cut off their temperatures will decrease

19、at ratesless than 0.2C/min. The temperature of the oil in each bathmay be determined by a calibrated temperature measuringdevice of suitable precision and accuracy. If the oil is notstirred, the junctions shall be placed in close proximity to thetemperature-measuring instrument. To ensure that the t

20、empera-tures of the junctions shall not be influenced by heat ofconduction along the specimen, the length of each specimenfrom the junction to the point where it leaves the surface of theoil shall not be less than 10 times the minimum cross-sectiondimension of the resistance material, nor less than

21、100 timesthe minimum cross section of the copper leads, and in no caseless than 2 in. (50.8 mm).6.2 Measurement of Electromotive ForceThe electromo-tive force shall be determined by a method that will give thevalue correct within 5 %. Three different methods of measuringthe electromotive force are i

22、n common use, namely:6.2.1 The method in which a potentiometer is used tocompare the unknown emf with that of a standard cell.6.2.2 The method in which the unknown emf is equated tothe difference of potential between the terminals of a standardresistor when a measured current flows through it.6.2.3

23、The method in which the emf is measured by thedeflection of a suitable measuring instrument.6.2.4 In any case, precautions shall be taken to ensure thatthere are no parasitic electromotive forces in the measuringcircuit, a condition which may be determined by placing bothjunctions in the same beaker

24、, in which case no appreciableelectromotive force shall be indicated.7. Polarity of the Metal7.1 The metal or alloy tested shall be considered to havepositive polarity when, in a circuit consisting of copper and themetal or alloy, the direction of current flow in the metal or alloyis from the juncti

25、on having the higher temperature to the onehaving the lower temperature.8. Report8.1 The report shall include the following:8.1.1 The character of the metal or alloy tested and theidentification of the specimen,8.1.2 The size, shape, and length of the specimen,8.1.3 Method of determining the tempera

26、tures of thejunctions,8.1.4 The temperature at each junction in degree Celsius,8.1.5 The type of apparatus used in measuring the electro-motive force,8.1.6 The observed electromotive force,8.1.7 The thermoelectric power, and8.1.8 The polarity of the metal or alloy tested.9. Precision and Bias9.1 The

27、 reproducibility of the test results depends on thecontrol used in making the connections and the control oftemperatures at the junctions. The bias will depend on theparameters listed for reproducibility and instrumentation usedto measure emf.9.2 The precision of this test method should be 1 % or le

28、ss.9.3 The bias of this test method is within 6 %.10. Keywords10.1 copper; electrical resistant alloys; potentiometer; ther-moelectric powerASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this

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