ASTM B84-90(1995)e1
(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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e1
Designation: B 84 – 90 (Reapproved 1995) An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Temperature-Resistance Constants of Alloy Wires for
Precision Resistors
This standard is issued under the fixed designation B 84; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Section 19 was added editorially in June 1995.
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 Procedure A covers 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
measured by apparatus capable of determining such changes to
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.
6.2 The connections from the specimen to the measuring
3. Apparatus
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
quality, a change in 1°C in room temperature is allowable.
4. Baths
6.4 The test current shall not be of such a magnitude as to
4.1 Baths for use from − 65 to + 15°C may consist of toluol,
produce an appreciable change in resistance of the specimen or
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 The liquid in these baths shall be of such quantity and so
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 value until the resistance has again become constant. If the
This test method is under the jurisdiction of ASTM Committee B-4 on Metallic
Materials for Thermostats and for Electrical Resistance, Heating, and Contacts, and
change in resistance is greater than 0.01 %, the test current is
is the direct responsibility of Subcommittee B04.01 on Electrical Contract Materi-
too large and shall be reduced until the foregoing limitation is
als.
reached.
Current edition approved May 25, 1990. Published January 1991. Originally
published as B 84 – 31. Last previous edition B 84 – 88. 6.5 The measurements shall be made in such a way that the
B84
effects of thermoelectromotive forces and parasitic currents are submerge entirely in the bath. For a check on the constancy of
avoided. When these effects are small, the resistance of the the specimen, make an initial resistance measurement at 25°C.
specimen may be obtained by either of the following methods: Raise the temperature of the bath or transfer the specimen to a
6.5.1 Obtain the galvanometer zero with the galvanometer bath maintained constant at the highest temperature at which
key open. Balance the bridge both with the direct and reversed measurements are to be made. When the specimen has attained
connection of the battery, the average value of the two results a constant resistance, record the reading of the measuring
being the resistance of the specimen. device and the temperature of the bath.
6.5.2 Obtain the zero of the galvanometer with the galva- 11.2 Decrease the temperature of the test specimen to the
nometer key closed and the battery key opened. A single next lower temperature either by cooling the bath and main-
balance of the bridge is then sufficient to obtain the resistance taining it constant at the next lower temperature, or by
of the specimen. removing the specimen to another bath maintained at the lower
temperature. When the resistance of the specimen has become
7. Sampling
constant, again make observations of resistance and tempera-
7.1 Take one test specimen from each continuous length of
ture.
the material to be tested.
11.3 In this manner, make a series of determinations of the
change of resistance with temperature for the desired descend-
8. Test Specimen
ing temperature range, measurements being taken at intervals
8.1 The test specimen shall be of a length that will give a
of approximately 10 % of the temperature range or any
resistance that can be measured to the required accuracy.
temperature interval specified by agreement between producer
8.2 If the wire is insulated, it may be wound in a circular,
and consumer.
open coil not less than 50 mm in diameter.
11.4 Test at not less than four temperatures.
8.3 If the wire is not insulated, it may be wound on an
11.5 Note the temperature of the measuring apparatus at
insulating form of a type that will not introduce strains in the
frequent intervals during the test of each specimen.
wire when subjected to temperature changes.
8.4 The tension used in winding shall be no more than
12. Procedure B
sufficient to produce a neat coil of insulated wire or to prevent
12.1 See Section 11, except 11.4. Tests shall be made at not
the touching of adjacent turns when bare wire is wound on an
less than three temperatures, including 25°C.
insulating form.
8.5 For fine wires of sufficiently high-resistivity alloys,
13. Resistance-Temperature Equation
straight wire specimens may be used. Precautions should be
13.1 Express the results in terms of the constants in an
taken to avoid the introduction of strains in the sample during
equation of the following form:
preparation.
R 5 R @11a~t 2 25!1b~t 225! #
t 25
9. Terminals
(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, or welded to each end of the specimen for use
R = resistance of the specimen in ohms at
t
as a terminal. The resistance of the copper terminals shall be temperature, °C, t,
less than 0.02 % of the resistance of the specimen. R = resistance of the specimen in ohms at the
standard temperature of 25°C,
9.2 If the resistance of the specimen is less than 10 V,so
t = temperature of specimen, °C, and
that it is necessary to use both current and potential terminals
a and b = temperature-resistance constants of the
in measuring the resistance, two copper wires may be brazed,
material.
soldered, or welded to each end of the specimen for use as
Temperature of maximum or minimum resistance
terminals. The terminals shall be placed so that the measured
=25°C−(a/2b)
potential does not include the potential drop in the current
connections.
NOTE 2—This equation will yield either a maximum or a minimum,
9.3 In coils made of fine wire where there is not sufficient depending on which exists in the temperature range in question. However,
this equation is normally used for those alloys such as manganin, having
rigidity in the coil itself to furnish a satisfactory support for the
a temperature-resistance curve approximating a parabola with a maximum
terminals, short lengths of thin glass or ceramic rods may be
near room temperature.
found across the coil to act as struts and furnish an anchorage
for the terminals.
14. Calculation of Constants
10. Preliminary Treatment of Specimen 14.1 The values of a, b and R may be determined by
selecting the measured values of R at three well-separated
t
10.1 The finished specimen shall be subjected to a baking
temperatures, inserting the values of R and t in the above
treatment as necessary to stabilize the resistance of the speci- t
equation to form three equations, and solving simultaneously
men. For manganin the treatment shall be at 140 6 10°C
the three equations for R , a, and b.
continuously for a period of 48 h. 25
14.2 When the measurements have not been made at exactly
11. Procedure A
25°C, or at other suitable temperatures, the calculation may b
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