1、Designation: B84 07 (Reapproved 2013)Standard Test Method forTemperature-Resistance Constants of Alloy Wires forPrecision Resistors1This standard is issued under the fixed designation B84; the number immediately following the designation indicates the year of originaladoption or, in the case of revi
2、sion, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers determination of the change ofresistance with temperature of alloy wires used fo
3、r resistancestandards and precision resistors for electrical apparatus.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use.
4、 It is theresponsibility of the user of 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 app
5、licability ofregulatory limitations prior to use.2. Significance and Use2.1 Procedure A covers the determination of the equation ofthe curve relating resistance and temperature where the curveapproximates a parabola. This test method may be used forwire of any metal or alloy over the temperature int
6、ervalappropriate to the material.2.2 Procedure B covers the determination of the meantemperature coefficient of resistance for wire of any metal oralloy over the temperature interval appropriate to the material.3. Apparatus3.1 The apparatus for making the test shall consist of one ormore baths for m
7、aintaining the specimen at the desiredtemperatures; thermometers for measuring the temperatures ofthe baths; and suitable means for measuring the resistance ofthe specimen. Details of the apparatus are given in Sections 4to 6.4. Baths4.1 Baths for use from 65 to +15C may consist of toluol,or equival
8、ent.4.2 Baths for use above 15 to 250C may consist ofchemically neutral oils with a low viscosity, having a flashpoint at least 50C higher than the temperature of use.4.3 The liquid in these baths shall be of such quantity and sowell stirred that the temperature in the region occupied by thespecimen
9、 and the thermometer will be uniform within 0.5Cfor any temperature between 65 and +100C, and within1.0C for any temperature above 100 to 250C. If the tempera-ture range is less than 100C, the uniformity of temperatureshall be proportionately closer.NOTE 1It is recommended that a solvent bath at roo
10、m temperatureshall be used to rinse specimens before immersion in any temperaturebath.5. Temperature Measurement Apparatus5.1 The temperature shall be measured to an accuracy of60.5C, or 1 % of temperature range, whichever is smaller.6. Resistance Measurement Apparatus6.1 The change of resistance of
11、 the specimen shall bemeasured by apparatus capable of determining such changes to0.001 % of the resistance of the specimen if the temperaturerange is 50C or more. If the temperature range is less than50C, the accuracy of the resistance change measurementsshall be correspondingly greater.6.2 The con
12、nections from the specimen to the measuringdevice shall be such that changes in the resistance of theseconnections due to changes in their temperature do notappreciably affect the measurement of the change in resistanceof the specimen.6.3 The temperature of the measuring apparatus shall notchange du
13、ring the test by an amount sufficient to introduceappreciable errors in the results. With apparatus of goodquality, a change in 1C in room temperature is allowable.6.4 The test current shall not be of such a magnitude as toproduce an appreciable change in resistance of the specimen ormeasuring appar
14、atus due to the heating effect. To determineexperimentally that the test current is not too large, the1This 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
15、 Heating Materials.Current edition approved May 1, 2013. Published May 2013. Originallyapproved in 1931. Last previous edition approved in 2007 as B84 07. DOI:10.1520/B0084-07R13.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1specime
16、n may be immersed in a bath having a temperature atwhich it has been found that the wire has a relatively largechange in resistance with temperature. Apply the test currentand maintain until the resistance of the specimen has becomeconstant. Then increase the current by 40 % and maintain atthis valu
17、e until the resistance has again become constant. If thechange in resistance is greater than 0.01 %, the test current istoo large and shall be reduced until the foregoing limitation isreached.6.5 The measurements shall be made in such a way that theeffects of thermoelectromotive forces and parasitic
18、 currents areavoided. When these effects are small, the resistance of thespecimen may be obtained by either of the following methods:6.5.1 Obtain the galvanometer zero with the galvanometerkey open. Balance the bridge both with the direct and reversedconnection of the battery, the average value of t
19、he two resultsbeing the resistance of the specimen.6.5.2 Obtain the zero of the galvanometer with the galva-nometer key closed and the battery key opened. A singlebalance of the bridge is then sufficient to obtain the resistanceof the specimen.7. Sampling7.1 Take one test specimen from each continuo
20、us length ofthe material to be tested.8. Test Specimen8.1 The test specimen shall be of a length that will give aresistance that can be measured to the required accuracy.8.2 If the wire is insulated, it may be wound in a circular,open coil not less than 50 mm in diameter.8.3 If the wire is not insul
21、ated, it may be wound on aninsulating form of a type that will not introduce strains in thewire when subjected to temperature changes.8.4 The tension used in winding shall be no more thansufficient to produce a neat coil of insulated wire or to preventthe touching of adjacent turns when bare wire is
22、 wound on aninsulating form.8.5 For fine wires of sufficiently high-resistivity alloys,straight wire specimens may be used. Precautions should betaken to avoid the introduction of strains in the sample duringpreparation.9. Terminals9.1 For specimens having a resistance so large that theresistance of
23、 the leads is negligible, a copper wire may bebrazed, soldered, or welded to each end of the specimen for useas a terminal. The resistance of the copper terminals shall beless than 0.02 % of the resistance of the specimen.9.2 If the resistance of the specimen is less than 10 ,sothat it is necessary
24、to use both current and potential terminalsin measuring the resistance, two copper wires may be brazed,soldered, or welded to each end of the specimen for use asterminals. The terminals shall be placed so that the measuredpotential does not include the potential drop in the currentconnections.9.3 In
25、 coils made of fine wire where there is not sufficientrigidity in the coil itself to furnish a satisfactory support for theterminals, short lengths of thin glass or ceramic rods may befound across the coil to act as struts and furnish an anchoragefor the terminals.10. Preliminary Treatment of Specim
26、en10.1 The finished specimen shall be subjected to a bakingtreatment as necessary to stabilize the resistance of the speci-men. For manganin the treatment shall be at 140 6 10Ccontinuously for a period of 48 h.11. Procedure A11.1 Connect the test specimen in the measuring circuit andsubmerge entirel
27、y in the bath. For a check on the constancy ofthe specimen, make an initial resistance measurement at 25C.Raise the temperature of the bath or transfer the specimen to abath maintained constant at the highest temperature at whichmeasurements are to be made. When the specimen has attaineda constant r
28、esistance, record the reading of the measuringdevice and the temperature of the bath.11.2 Decrease the temperature of the test specimen to thenext lower temperature either by cooling the bath and main-taining it constant at the next lower temperature, or byremoving the specimen to another bath maint
29、ained at the lowertemperature. When the resistance of the specimen has becomeconstant, again make observations of resistance and tempera-ture.11.3 In this manner, make a series of determinations of thechange of resistance with temperature for the desired descend-ing temperature range, measurements b
30、eing taken at intervalsof approximately 10 % of the temperature range or anytemperature interval specified by agreement between producerand consumer.11.4 Test at not less than four temperatures.11.5 Note the temperature of the measuring apparatus atfrequent intervals during the test of each specimen
31、.12. Procedure B12.1 See Section 11, except 11.4. Tests shall be made at notless than three temperatures, including 25C.13. Resistance-Temperature Equation13.1 Express the results in terms of the constants in anequation of the following form:Rt5 R2511t 2 25!1t 2 25!2# (1)where:Rt= resistance of the
32、specimen in ohms at temperature,C, t,R25= resistance of the specimen in ohms at the standardtemperature of 25C,t = temperature of specimen, C, and and = temperature-resistance constants of the material.Temperature of maximum or minimum resistance=25C(/2)B84 07 (2013)2NOTE 2This equation will yield e
33、ither a maximum or a minimum,depending on which exists in the temperature range in question. However,this equation is normally used for those alloys such as manganin, havinga temperature-resistance curve approximating a parabola with a maximumnear room temperature.14. Calculation of Constants14.1 Th
34、e values of , and R25may be determined byselecting the measured values of Rtat three well-separatedtemperatures, inserting the values of Rtand t in the aboveequation to form three equations, and solving simultaneouslythe three equations for R25, , and .14.2 When the measurements have not been made a
35、t exactly25C, or at other suitable temperatures, the calculation may besimplified by plotting a curve from the observed values ofresistance and temperature, from which curve R25may be readdirectly. Two additional points may then be selected on thecurve, preferably one at t1, at least 5C below the re
36、ferencetemperature of 25C, and a second temperature, t2near thehighest temperature measured but satisfying the followingrelation:K25 2 t1! 5 t22 25 5 Kt (2)where K is, for ease of calculation, generally taken as aninteger.NOTE 3Example: If t1is 10C below the reference temperature thent2should be 10
37、or 20 or 30C etc., above the reference temperature forgreatest ease of calculation, so that K = 1 or 2 or 3, respectively.14.3 If R1is the resistance at the temperature t1, and R2isthe resistance at the temperature t2, then: 5 R22 R25! 2 K2R12 R25!#/R25KK11!t (3) 5 K R12 R25! 1 R22 R25!/R25K K11!t!2
38、(4)If K = 1, this simplifies to: 5 R22 R1!/2R25t (5) 5 R11R22 2R25!/2R25t!2(6)If, instead of measuring the actual resistances at the differenttemperatures, the change in resistance relative to the resistanceat 25C is measured, the above equations take a slightlydifferent form, as follows: Let R1repr
39、esent the change inresistance in ohms per ohm in going from 25C to t1, and R2the similar change in going from 25C to t2. That is:R15 R12 R25!/R25(7)andR25 R22 R25!/R25(8)Then 5 R22 K2R1!/K K11!t (9) 5 KR11R2!/KK11!t!2(10)If K = 1, this simplifies to: 5 R22 R1!/2t (11) 5 R11R2!/1t!2(12)NOTE 4A useful
40、 alternative method of calculation is presented asfollows: The resistance-temperature equation is referred to 0C, andrelative resistance values are used. For example, over the useful rangefrom 15 to 35C, the resistance-temperature curve of manganin isparabolic and of the form:Pt5 P01At1Bt2(13)where:
41、Pt= %, ratio of the resistance of the specimen at t C to the resistanceof the standard resistor at 25C, expressed in percent,P0= %, ratio of the resistance of the specimen at 0C to the resistanceof the standard resistor at 25C, expressed in percent, andA and B are constants calculated from resistanc
42、e measurements made atdifferent temperatures. One method of measurement used in productiontesting is to compare the resistance of the test sample to that of a stableresistor of known characteristics maintained at reference temperature25C. The resistance is approximately the same as the test sample a
43、ndmeasurements usually are made directly in percentages (for example,100.008 %). If measurements are made at four temperatures t1,t2,t3, andt4between 15 and 35C, and the corresponding ratios of test sampleresistance to standard resistor are measured in percentages as P1,P2,P3,and P4, then the consta
44、nts A and B, the peak temperature, and temperaturecoefficient may be calculated from the following equations:A 512FP32 P1t32 t11P22 P1t42 t12 t31tr12t1!G (14)B 5P32 P1t32 t11P42 P1t42 t12 2P22 P1t22 t1t31t42 2t2(15)The peak temperature is (A/2B) and the temperature coefficient be-tween temperature t
45、 and the peak temperature in percent per degreeCelsius is (A +2Bt)/2. Then 5 A150B!/100 (16) 5 B/100 (17)15. Procedure AReport15.1 Report the following information:15.1.1 Identification of specimen,15.1.2 Description of material and its insulation,15.1.3 Length of wire in specimen and approximateres
46、istance,15.1.4 Tabular list of resistances and temperatures in theorder taken,15.1.5 Temperature of measuring apparatus and room atstart and finish of test,15.1.6 Values of t and R used in calculating and ,15.1.7 Values calculated for the temperature-resistance con-stants and , and15.1.8 Temperature
47、 of the specimen at which the change ofresistance with temperature is zero, if such occurs within themeasured range.16. Procedure BReport16.1 Report the following information:16.1.1 Identification of specimen,16.1.2 Description of material and its insulation,16.1.3 Length of wire in specimen and app
48、roximateresistance,16.1.4 Tabular list of resistance and temperatures in theorder taken,16.1.5 Temperature of measuring apparatus and room atstart and finish of test, and16.1.6 Values of temperature coefficient of resistance inmicrohms per ohm per degree Celsius or parts per million perB84 07 (2013)
49、3degree Celsius. These values shall be calculated for each testtemperature, using the following equation:Mean temperature coefficient of resistance over specified (18)temperature interval 5 R12 R25!/R25T12 25!# 3106where:R1= resistance of specimen at test temperature, ,R25= resistance of specimen at 25C, , andT1= temperature of the bath, C.17. Record17.1 The measurements shall be recorded on a data sheetsimilar to that shown in Table 1.18. Precision an
