1、Designation: B 77 07Standard Test Method forThermoelectric Power of Electrical-Resistance Alloys1This standard is issued under the fixed designation B 77; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision. A
2、 number in parentheses indicates the year of last reapproval. A superscriptepsilon (e) 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 the temperature
3、s of the junctions lie between 0 and100C.1.2 The values stated in inch-pound units are the preferredunit. The values in parentheses are for information only.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user o
4、f this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet (MSDS) for this product/materialas provided by the manufacturer, to establish appropriatesafety and health practices, and determine the applicability ofregulatory limitations pr
5、ior to use.2. Referenced Documents2.1 ASTM Standards:2B3 Specification for Soft or Annealed Copper Wire3. Terminology3.1 thermoelectric power, Q, nthe electromotive force inan electric circuit consisting of two metals when the junctionsbetween them have a difference in temperature of 1C.3.1.1 Discus
6、sionExperimentally, it has been found thatthe thermoelectric power of two metals is not a constant butdepends on the mean temperature of the junctions. However,over a range of temperature from 0 to 100C it is usuallysufficient to assume that the thermoelectric power is indepen-dent of temperature so
7、 that for this range of temperature:Q 5 E/t8 2 t!where:E = the electromotive force developed in the circuit,t8 = the higher temperature at one junction, C, andt = 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
8、different metals for use in resistance apparatus in whicha low thermoelectric power is desired. As most electric circuitsare largely composed of copper, the thermoelectric power of aresistance metal will generally be measured against copper.5. Test Specimen5.1 The metal or alloy to be tested shall b
9、e 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 end of the specimen a copper lead ofconvenient size shall be fastened. These leads shall make goodelectrical contact with the specimen, su
10、ch as that obtained bywelding, brazing, or soldering. Slight impurities in the copperhave a negligible effect on the thermoelectric power.NOTE 1When necessary to specify the quality of the copper leads,reference should be made to Specification B3.6. Procedure6.1 Measurement of TemperatureAs a matter
11、 of precau-tion, the average temperature used in determining the thermo-electric power shall be approximately the same as that to whichthe material will be subjected in practice, and in no case shallthe temperature difference between the two junctions be lessthan 20C. The temperature at each of two
12、junctions shall bemeasured by a device that is sufficiently accurate to determinethe temperature difference within 5 %. A convenient methodfor determining the temperatures of the junctions is to immerseeach junction in separate oil baths maintained at the desiredtemperatures. Baths that are stirred
13、and the temperatures ofwhich are thermostatically controlled are to be preferred.However, beakers of oil which are supported by blocks ofmetal, sand baths, or other means may be used, provided thethermal capacity of these assemblies is such that when the heatis cut off their temperatures will decrea
14、se at rates less than0.2C/min. The temperature of the oil in each bath may be1This test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and is the direct responsibility of SubcommitteeB02.10 on Thermostat Metals and Electrical Resistance Heating Materials.Curren
15、t edition approved May 1, 2007. Published June 2007. Originallyapproved in 1930. Last previous edition approved in 2001 as B 77 81 (2001).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
16、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.determined by a calibrated temperature measuring device ofsuitable precision and accuracy. If the oil is not
17、 stirred, thejunctions shall be placed in close proximity to the temperature-measuring instrument. To ensure that the temperatures of thejunctions shall not be influenced by heat of conduction alongthe specimen, the length of each specimen from the junction tothe point where it leaves the surface of
18、 the oil shall not be lessthan 10 times the minimum cross-section dimension of theresistance material, nor less than 100 times the minimum crosssection of the copper leads, and in no case less than 2 in. (50.8mm).6.2 Measurement of Electromotive ForceThe electromo-tive force shall be determined by a
19、 method that will give thevalue correct within 5 %. Three different methods of measuringthe electromotive force are in 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 toth
20、e difference of potential between the terminals of a standardresistor when a measured current flows through it.6.2.3 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 electrom
21、otive forces in the measuringcircuit, a condition which may be determined by placing bothjunctions in the same beaker, 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 circ
22、uit consisting of copper and themetal or alloy, the direction of current flow in the metal or alloyis from the junction 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 theide
23、ntification of the specimen,8.1.2 The size, shape, and length of the specimen,8.1.3 Method of determining the temperatures of the junc-tions,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 electromotiv
24、e force,8.1.7 The thermoelectric power, and8.1.8 The polarity of the metal or alloy tested.9. Precision and Bias9.1 The 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 list
25、ed for reproducibility and instrumentation usedto measure emf.9.2 The precision of this test method should be 1 % or less.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 resp
26、ecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This s
27、tandard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM Interna
28、tional Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown bel
29、ow.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).B77072
