ASTM B114-90(1995)e1

NOTICE: This standard has either been superseded and replaced by a new version or
withdrawn. Contact ASTM International (www.astm.org) for the latest information.
e1
Designation: B 114 – 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 Sheet Materials for
Shunts and Precision Resistors
This standard is issued under the fixed designation B 114; 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 17 was added editorially in June 1995.
1. Scope specimen. These terminals shall be either soldered or clamped
in such a manner that there will be no change of current
1.1 This test method covers the determination of the change
distribution in the specimen during the test.
of resistance with temperature of sheet materials used for
5.2 Potential terminals, one at each end, shall be located at
shunts and precision resistors for electrical apparatus. It is
a distance not less than two times the width of the specimen
applicable to materials normally used in the temperature range
from the current terminals. These terminals shall be attached at
of from 0 to 80°C.
the center of the width of the specimen either by soldering to
1.2 The values stated in inch-pound units are to be regarded
ears cut out of the specimen (Note 2) as shown in Fig. 1 or by
as the standard. The metric equivalents of inch-pound units
clamps, each of which presses a single sharp point into the
may be approximate.
material.
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 1
NOTE 2—The ears shall be cut so that they are about ⁄2 in. (12.7 mm)
responsibility of the user of this standard to establish appro-
in length and ⁄8 in. (3.2 mm) in width. The cut shall be clean and free from
slivers at the junction of the ear and the specimen. Before cutting the ears,
priate safety and health practices and determine the applica-
it is desirable to drill two small holes with a sharp drill where the ear will
bility of regulatory limitations prior to use.
be jointed to the specimen.
2. Referenced Documents
6. Preliminary Treatment for Manganin Samples
2.1 ASTM Standards:
6.1 In the case of manganin materials, after all the mechani-
B 84 Test Method for Temperature-Resistance Constants of
cal work has been finished, the specimen shall be given one
Alloy Wires for Precision Resistors
heat treatment of 48 h at 140 6 5.0°C and then cooled to room
3. Significance and Use
temperature.
6.2 The specimen shall then be given a dip in a nitric acid
3.1 This test method covers the determination of the change
solution (50 %) to remove the copper film (which can be
of resistance with temperature for precision resistors and
judged by the color of the specimen) and then thoroughly
shunts made from sheet materials.
scrubbed in running water.
3.2 Materials normally used in the temperature range from 0
to 80°C may be tested using this test method.
7. Apparatus
4. Test Specimen
7.1 The apparatus for making the test shall consist of one or
more baths for maintaining the specimen at the desired
4.1 The test specimen shall be of such dimensions that its
temperature, thermometers for measuring the temperatures of
electrical resistance can be measured to the required accuracy.
the baths, and suitable means for measuring the resistance of
NOTE 1—Measurements are simplified if the specimen has a resistance
the specimen.
of 0.01 V or more. The specimen may be bent in the form of a “U” to
facilitate handling.
8. Baths
8.1 Each bath shall consist of chemically neutral oil. The oil
5. Terminals
shall be of such quantity and so well stirred that the tempera-
5.1 A current terminal shall be attached to each end of the
ture in the region occupied by the specimen and the thermom-
eter shall be uniform within 0.2°C for any temperature between
1 0 and 80°C.
This test method is under the jurisdiction of ASTM Committee B-4 on Metallic
8.2 In an automatically controlled bath, the temperature of
Materials for Thermostats and for Electrical Resistance, Heating, and Contacts and
is the direct responsibility of Subcommittee B04.01 on Electrical Heating and
the bath at any time during the test at any temperature level
Resistance.
shall not differ from its mean temperature by more than 0.2°C.
Current edition approved May 25, 1990. Published January 1991. Originally
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In a manually controlled bath, the rate of change of tempera-
published as B 114 – 38. Last previous edition B 114 – 45 (1981) .
Annual Book of ASTM Standards, Vol 03.04. ture shall not exceed 0.2°C/min.
B114
effects of thermoelectromotive forces and parasitic currents are
avoided. When these effects are small, the resistance of the
specimen when measured by a Kelvin bridge may be obtained
by either of two methods. In the first method, the galvanometer
zero shall be obtained with the galvanometer key open. The
bridge shall be balanced both with the direct and reversed
connection of the battery, the average value of the two results
being the resistance of the specimen. In the second method, the
zero of the galvanometer shall be obtained with the galvanom-
eter key closed and the battery key open. A single balance of
the bridge is then sufficient to obtain the resistance of the
specimen.
11. Procedure
11.1 Connect the test specimen in the measuring circuit and
submerge entirely in the oil bath. For a check on the constancy
of the specimen, make an initial resistance measurement at
room temperature. Raise the temperature of the oil bath or
transfer the specimen to a bath maintained constant at the
highest temperature at which measurements are to be made.
When the test specimen has attained a constant resistance,
record the reading of the measuring device and the temperature
of the bath.
FIG. 1 Test Specimen Showing Terminal Connections
11.2 Decrease the temperature of the test specimen to the
next lower temperatures either by cooling the bath and main-
9. Temperature Measurement
taining it constant at the next lower temperature, or by
removing the specimen to another bath maintained at the lower
9.1 The temperature shall be measured either with a labo-
temperature. When the resistance of the specimen has become
ratory type of mercurial thermometer or a resistance thermom-
constant, again make observations of resistance and tempera-
eter. The thermometer shall have sufficient sensitivity to
ture.
indicate temperature changes of 0.1°C. It shall be sufficiently
11.3 In this manner make a series of determinations of the
accurate to measure temperature differences to 0.2°C in the
change of resistance with temperature for the desired descend-
range from 0 to 80°C.
ing temperature range.
10. Resistance Measurements
11.4 Take measurements at a sufficient number of tempera-
tures to determine the characteristics of the material. In order to
10.1 The change of resistance of the specimen shall be
calculate a resistance-temperature equation, tests at three
measured by apparatus capable of determining such changes to
temperatures are required. If an independent check is to be
0.001 % of the resistance of the specimen. A Kelvin double
made, make observations of at least five temperatures. For
bridge, digital ohmmeter, or equivalent is suitable for this
plotting a curve, six or more observations are generally made.
purpose (see Appendix X1).
11.5 Note the temperature of the measuring apparatus at
10.2 The temperature of the measuring apparatus shall not
frequent intervals during the test of each specimen.
change during the test by an amount sufficient to introduce
appreciable errors in the results. With apparatus of good
12. Resistance-Temperature Equation
quality, a change of 1°C in its temperature is allowable.
12.1 Express the results in terms of the constants in an
10.3 The test current shall not be of such a magnitude as to
equation of the following form:
produce an appreciable change in resistance of the specimen or
measuring apparatus due to the heating effect. The dimensions
R 5 R @11a~t 2 25!1b~t 225! # (1)
t 25
of the specimen should be such that the power dissipated shall
2 2
not exceed 0.02 W/in. (0.003 W/cm ) of exposed surface. To
where:
determine experimentally that the test current is not too large,
R = resistance of the specimen in ohms at
t
the specimen may be immersed in a bath having a temperature
temperature, °C, t,
at which it has been found that the sheet has a relatively large
R = resistance of the specimen in ohms at the
change in resistance with temperature. The test current shall be
standard temperature of 25°C,
applied and maintained until the resistance of the specimen has
t = temperature of specimen, °C, and
become constant. The current shall then be increased by 40 % a and b = temperature-resistance constants of the material.
Temperature of maximum or minimum resistance
and maintained at this value until the resistance has again
=25°C−(a/2b)
become constant. If the change in resistance is greater than
0.001 %, the test current is too large and shall be reduced until
NOTE 3—This equation will yield either a maximum or a minimum,
the foregoing limitation is reached.
depending on which exists in the temperature range in question. However,
10.4 The measurements shall be made in such a way that the this equation is normally used for those alloys such as manganin, having
B114
a temperature-resistance curve approximating a parabola with a maximum
where:
near room temperature.
P = ratio of the resistance of the specimen at t °C to the
t
resistance of the standard resistor at 25°C,% ,
13. Calculation of Constants
P = ratio of the resistance of the specimen at 0°C to the
13.1 The values of a, b, and R may be determined by
25 resistance of the standard resistor at 25°C, %, and
selecting the measured values of R at three well-separated
A and B are constants calculated from resistance measurements
t
temperatures, inserting the va
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