ASTM B114-90(2001)
(Test Method)Standard Test Method for Temperature-Resistance Constants of Sheet Materials for Shunts and Precision Resistors
Standard Test Method for Temperature-Resistance Constants of Sheet Materials for Shunts and Precision Resistors
SCOPE
1.1 This test method covers the determination of the change of resistance with temperature of sheet materials used for shunts and precision resistors for electrical apparatus. It is applicable to materials normally used in the temperature range of from 0 to 80oC.
1.2 The values stated in inch-pound units are to be regarded as the standard. The metric equivalents of inch-pound units may be approximate.
1.3 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:B114–90(Reapproved2001)
Standard Test Method for
Temperature-Resistance Constants of Sheet Materials for
Shunts and Precision Resistors
This standard is issued under the fixed designation B114; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope in such a manner that there will be no change of current
distribution in the specimen during the test.
1.1 This test method covers the determination of the change
5.2 Potential terminals, one at each end, shall be located at
of resistance with temperature of sheet materials used for
a distance not less than two times the width of the specimen
shunts and precision resistors for electrical apparatus. It is
fromthecurrentterminals.Theseterminalsshallbeattachedat
applicable to materials normally used in the temperature range
the center of the width of the specimen either by soldering to
of from 0 to 80°C.
ears cut out of the specimen (Note 2) as shown in Fig. 1 or by
1.2 The values stated in inch-pound units are to be regarded
clamps, each of which presses a single sharp point into the
as the standard. The metric equivalents of inch-pound units
material.
may be approximate.
1.3 This standard does not purport to address all of the 1
NOTE 2—The ears shall be cut so that they are about ⁄2 in. (12.7 mm)
safety concerns, if any, associated with its use. It is the inlengthand ⁄8in.(3.2mm)inwidth.Thecutshallbecleanandfreefrom
sliversatthejunctionoftheearandthespecimen.Beforecuttingtheears,
responsibility of the user of this standard to establish appro-
it is desirable to drill two small holes with a sharp drill where the ear will
priate safety and health practices and determine the applica-
be jointed to the specimen.
bility of regulatory limitations prior to use.
6. Preliminary Treatment for Manganin Samples
2. Referenced Documents
6.1 Inthecaseofmanganinmaterials,afterallthemechani-
2.1 ASTM Standards:
cal work has been finished, the specimen shall be given one
B84 Test Method for Temperature-Resistance Constants of
2 heat treatment of 48h at 140 6 5.0°C and then cooled to room
Alloy Wires for Precision Resistors
temperature.
6.2 The specimen shall then be given a dip in a nitric acid
3. Significance and Use
solution (50%) to remove the copper film (which can be
3.1 This test method covers the determination of the change
judged by the color of the specimen) and then thoroughly
of resistance with temperature for precision resistors and
scrubbed in running water.
shunts made from sheet materials.
3.2 Materialsnormallyusedinthetemperaturerangefrom0
7. Apparatus
to 80°C may be tested using this test method.
7.1 The apparatus for making the test shall consist of one or
more baths for maintaining the specimen at the desired
4. Test Specimen
temperature, thermometers for measuring the temperatures of
4.1 The test specimen shall be of such dimensions that its
the baths, and suitable means for measuring the resistance of
electrical resistance can be measured to the required accuracy.
the specimen.
NOTE 1—Measurements are simplified if the specimen has a resistance
of 0.01 V or more. The specimen may be bent in the form of a “U” to 8. Baths
facilitate handling.
8.1 Eachbathshallconsistofchemicallyneutraloil.Theoil
shall be of such quantity and so well stirred that the tempera-
5. Terminals
ture in the region occupied by the specimen and the thermom-
5.1 A current terminal shall be attached to each end of the
etershallbeuniformwithin0.2°Cforanytemperaturebetween
specimen. These terminals shall be either soldered or clamped
0 and 80°C.
8.2 In an automatically controlled bath, the temperature of
This test method is under the jurisdiction of ASTM Committee B02 on
the bath at any time during the test at any temperature level
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
shall not differ from its mean temperature by more than 0.2°C.
B02.10 on Thermostat Metals.
In a manually controlled bath, the rate of change of tempera-
Current edition approved May 25, 1990. Published January 1991. Originally
e1
ture shall not exceed 0.2°C/min.
published as B114–38. Last previous edition B114–45(1981) .
Annual Book of ASTM Standards, Vol 03.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B114–90 (2001)
10.4 Themeasurementsshallbemadeinsuchawaythatthe
effectsofthermoelectromotiveforcesandparasiticcurrentsare
avoided. When these effects are small, the resistance of the
specimen when measured by a Kelvin bridge may be obtained
byeitheroftwomethods.Inthefirstmethod,thegalvanometer
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
beingtheresistanceofthespecimen.Inthesecondmethod,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,
recordthereadingofthemeasuringdeviceandthetemperature
FIG. 1 Test Specimen Showing Terminal Connections
of the bath.
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
9.1 The temperature shall be measured either with a labo-
removingthespecimentoanotherbathmaintainedatthelower
ratory type of mercurial thermometer or a resistance thermom-
temperature. When the resistance of the specimen has become
eter. The thermometer shall have sufficient sensitivity to
constant, again make observations of resistance and tempera-
indicate temperature changes of 0.1°C. It shall be sufficiently
ture.
accurate to measure temperature differences to 0.2°C in the
11.3 In this manner make a series of determinations of the
range from 0 to 80°C.
change of resistance with temperature for the desired descend-
ing temperature range.
10. Resistance Measurements
11.4 Take measurements at a sufficient number of tempera-
10.1 The change of resistance of the specimen shall be turestodeterminethecharacteristicsofthematerial.Inorderto
measuredbyapparatuscapableofdeterminingsuchchangesto calculate a resistance-temperature equation, tests at three
0.001% of the resistance of the specimen. A Kelvin double temperatures are required. If an independent check is to be
bridge, digital ohmmeter, or equivalent is suitable for this made, make observations of at least five temperatures. For
purpose (see Appendix X1). plotting a curve, six or more observations are generally made.
10.2 The temperature of the measuring apparatus shall not 11.5 Note the temperature of the measuring apparatus at
change during the test by an amount sufficient to introduce frequent intervals during the test of each specimen.
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:
produceanappreciablechangeinresistanceofthespecimenor
measuring apparatus due to the heating effect. The dimensions 2
R 5 R @11a~t 225!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 tempera-
the specimen may be immersed in a bath having a temperature t
ture, °C, t,
at which it has been found that the sheet has a relatively large
R = resistance of the specimen in ohms at the stan-
changeinresistancewithtemperature.Thetestcurrentshallbe
dard temperature of 25°C,
appliedandmaintaineduntiltheresistanceofthespecimenhas
t = temperature of specimen, °C, and
become constant. The current shall then be increased by 40%
a and b = temperature-resistanceconstantsofthematerial.
and maintained at this value until the resistance has again
Temperature of maximum or minimum resistance
become constant. If the change in resistance is greater than
=25°C−(a/2b)
0.001%, the test current is too large and shall be reduced until
the foregoing limitation is reached. NOTE 3—This equation will yield either a maximum or a minimum,
B114–90 (2001)
dependingonwhichexistsinthetemperaturerangeinquestion.However, a5~DR 2DR !/2Dt (11)
2 1
this equation is normally used for those alloys such as manganin, having
atemperature-resistancecurveapproximatingaparabolawithamaximum
b5~DR 1DR !/1~Dt! (12)
1 2
near room temperature.
13. Calculation of Constants
NOTE 5—A useful alternative method of calculation is presented as
follows: The resistance-temperature equation is referred to 0°C, and
13.1 The values of a, b, and R may be determined by
relative resistance values are used. For example, over the useful range
selecting the measured values of R at three well-separated
t
from 15 to 35°C, the resistance-temperature curve of manganin is
temperatures, inserting the values of R and t in the preceding
parabolic and of the form:
t
section equation to form three equations, and solving simulta-
P 5 P 1 At 1 Bt (13)
t 0
neously the three equations for R , a, and b.
13.2 Whenthemeasurementshavenotbeenmadeatexactly
where:
25°C, or at o
...
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