ASTM B84-90(2001)
(Test Method)Standard Test Method for Temperature-Resistance Constants of Alloy Wires for Precision Resistors
Standard Test Method for Temperature-Resistance Constants of Alloy Wires for Precision Resistors
SCOPE
1.1 This test method covers determination of the change of resistance with temperature of alloy wires used for resistance standards and precision resistors for electrical apparatus.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:B84–90(Reapproved2001)
Standard Test Method for
Temperature-Resistance Constants of Alloy Wires for
Precision Resistors
ThisstandardisissuedunderthefixeddesignationB84;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope specimen and the thermometer will be uniform within 0.5°C
for any temperature between − 65 and + 100°C, and within
1.1 This test method covers determination of the change of
1.0°C for any temperature above 100 to 250°C. If the tempera-
resistance with temperature of alloy wires used for resistance
ture range is less than 100°C, the uniformity of temperature
standards and precision resistors for electrical apparatus.
shall be proportionately closer.
1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
NOTE 1—It is recommended that a solvent bath at room temperature
responsibility of the user of this standard to establish appro- shall be used to rinse specimens before immersion in any temperature
bath.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
5. Temperature Measurement Apparatus
2. Significance and Use
5.1 The temperature shall be measured to an accuracy of
60.5°C, or 1% of temperature range, whichever is smaller.
2.1 ProcedureAcovers the determination of the equation of
the curve relating resistance and temperature where the curve
6. Resistance Measurement Apparatus
approximates a parabola. This test method may be used for
6.1 The change of resistance of the specimen shall be
wire of any metal or alloy over the temperature interval
measuredbyapparatuscapableofdeterminingsuchchangesto
appropriate to the material.
0.001% of the resistance of the specimen if the temperature
2.2 Procedure B covers the determination of the mean
range is 50°C or more. If the temperature range is less than
temperature coefficient of resistance for wire of any metal or
50°C, the accuracy of the resistance change measurements
alloy over the temperature interval appropriate to the material.
shall be correspondingly greater.
3. Apparatus
6.2 The connections from the specimen to the measuring
device shall be such that changes in the resistance of these
3.1 The apparatus for making the test shall consist of one or
connections due to changes in their temperature do not
more baths for maintaining the specimen at the desired
appreciably affect the measurement of the change in resistance
temperatures; thermometers for measuring the temperatures of
of the specimen.
the baths; and suitable means for measuring the resistance of
6.3 The temperature of the measuring apparatus shall not
the specimen. Details of the apparatus are given in Sections 4
change during the test by an amount sufficient to introduce
to 6.
appreciable errors in the results. With apparatus of good
4. Baths
quality, a change in 1°C in room temperature is allowable.
6.4 The test current shall not be of such a magnitude as to
4.1 Bathsforusefrom−65to+15°Cmayconsistoftoluol,
produceanappreciablechangeinresistanceofthespecimenor
or equivalent.
measuring apparatus due to the heating effect. To determine
4.2 Baths for use above 15 to 250°C may consist of
experimentally that the test current is not too large, the
chemically neutral oils with a low viscosity, having a flash
specimen may be immersed in a bath having a temperature at
point at least 50°C higher than the temperature of use.
which it has been found that the wire has a relatively large
4.3 Theliquidinthesebathsshallbeofsuchquantityandso
change in resistance with temperature. Apply the test current
well stirred that the temperature in the region occupied by the
and maintain until the resistance of the specimen has become
constant. Then increase the current by 40% and maintain at
This test method is under the jurisdiction of ASTM Committee B02 on
thisvalueuntiltheresistancehasagainbecomeconstant.Ifthe
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
B02.10 on Thermostat Metals.
Current edition approved May 25, 1990. Published January 1991. Originally
published as B84–31. Last previous edition B84–88.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B84–90 (2001)
change in resistance is greater than 0.01%, the test current is men. For manganin the treatment shall be at 140 6 10°C
too large and shall be reduced until the foregoing limitation is continuously for a period of 48 h.
reached.
11. Procedure A
6.5 The measurements shall be made in such a way that the
effectsofthermoelectromotiveforcesandparasiticcurrentsare
11.1 Connect the test specimen in the measuring circuit and
avoided. When these effects are small, the resistance of the
submerge entirely in the bath. For a check on the constancy of
specimen may be obtained by either of the following methods:
the specimen, make an initial resistance measurement at 25°C.
6.5.1 Obtain the galvanometer zero with the galvanometer
Raise the temperature of the bath or transfer the specimen to a
key open. Balance the bridge both with the direct and reversed
bath maintained constant at the highest temperature at which
connection of the battery, the average value of the two results
measurementsaretobemade.Whenthespecimenhasattained
being the resistance of the specimen.
a constant resistance, record the reading of the measuring
6.5.2 Obtain the zero of the galvanometer with the galva-
device and the temperature of the bath.
nometer key closed and the battery key opened. A single
11.2 Decrease the temperature of the test specimen to the
balance of the bridge is then sufficient to obtain the resistance
next lower temperature either by cooling the bath and main-
of the specimen.
taining it constant at the next lower temperature, or by
removingthespecimentoanotherbathmaintainedatthelower
7. Sampling
temperature. When the resistance of the specimen has become
7.1 Take one test specimen from each continuous length of
constant, again make observations of resistance and tempera-
the material to be tested.
ture.
11.3 In this manner, make a series of determinations of the
8. Test Specimen
change of resistance with temperature for the desired descend-
8.1 The test specimen shall be of a length that will give a
ing temperature range, measurements being taken at intervals
resistance that can be measured to the required accuracy.
of approximately 10% of the temperature range or any
8.2 If the wire is insulated, it may be wound in a circular,
temperature interval specified by agreement between producer
open coil not less than 50 mm in diameter.
and consumer.
8.3 If the wire is not insulated, it may be wound on an
11.4 Test at not less than four temperatures.
insulating form of a type that will not introduce strains in the
11.5 Note the temperature of the measuring apparatus at
wire when subjected to temperature changes.
frequent intervals during the test of each specimen.
8.4 The tension used in winding shall be no more than
sufficient to produce a neat coil of insulated wire or to prevent 12. Procedure B
the touching of adjacent turns when bare wire is wound on an
12.1 See Section 11, except 11.4. Tests shall be made at not
insulating form.
less than three temperatures, including 25°C.
8.5 For fine wires of sufficiently high-resistivity alloys,
straight wire specimens may be used. Precautions should be
13. Resistance-Temperature Equation
taken to avoid the introduction of strains in the sample during
13.1 Express the results in terms of the constants in an
preparation.
equation of the following form:
9. Terminals
R 5 R @11a~t 225!1b~t 225! #
t 25
(1)
9.1 For specimens having a resistance so large that the
resistance of the leads is negligible, a copper wire may be
where:
brazed,soldered,orweldedtoeachendofthespecimenforuse
R = resistance of the specimen in ohms at tempera-
t
as a terminal. The resistance of the copper terminals shall be
ture, °C, t,
less than 0.02% of the resistance of the specimen.
R = resistance of the specimen in ohms at the
9.2 If the resistance of the specimen is less than 10 V,so
standard temperature of 25°C,
that it is necessary to use both current and potential terminals
t = temperature of specimen, °C, and
in measuring the resistance, two copper wires may be brazed,
a and b = temperature-resistance constants of the mate-
soldered, or welded to each end of the specimen for use as
rial.
terminals. The terminals shall be placed so that the measured
Temperature of maximum or minimum resistance
potential does not include the potential drop in the current
=25°C−(a/2b)
connections.
9.3 In coils made of fine wire where there is not sufficient
NOTE 2—This equation will yield either a maximum or a minimum,
rigidityinthecoilitselftofurnishasatisfactorysupportforthe
dependingonwhichexistsinthetemperaturerangeinquestion.However,
terminals, short lengths of thin glass or ceramic rods may be
this equation is normally used for those alloys such as manganin, having
found across the coil to act as struts and furnish an anchorage
atemperature-resistancecurveapproximatingaparabolawithamaximum
for the terminals. near room temperature.
10. Preliminary Treatment of Specimen 14. Calculation of Constants
10.1 The finished specimen shall be subjected to a baking 14.1 The values of a, b and R may be determined by
treatment as necessary to stabilize the resistance of the speci- selecting the measured values of R at three well-separated
t
B84–90 (2001)
temperatures, inserting the values of R and t in the above
where:
t
P = %,ratiooftheresistanceofthespecimenatt°Ctotheresistance
equation to form three equations, and solving simultaneously
t
of the standard resistor at 25°C, expressed in percent,
the three equations for R , a, and b.
P = %,ratiooftheresistanceofthespecimenat0°Ctotheresistance
14.2 Whenthemeasurementshavenotbeenmadeatexactly
of the standard resistor at 25°C, expressed in p
...
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