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Constantan

Alloy of copper and nickel

Field	Value
name	Constantan
image	Konstantandraht.jpg
caption	A spool of Constantan wire
type	Copper-nickel alloy
density	8885 kg/m3
youngs_modulus	162 GPa
tensile_strength	~450 MPa
elongation	~0.25%
melting_point
surface_resistivity	0.56 μΩ·m

| thermal_conductivity kg·K)

Constantan refers to a copper-nickel alloy commonly used for its stable electrical resistance across a wide range of temperatures. Alternatively it is known in various contexts as Eureka, Advance, or Ferry. It usually consists of 55% copper and 45% nickel. Its main feature is the low thermal variation of its resistivity, which is constant over a wide range of temperatures. Other alloys with similarly low temperature coefficients are known, such as manganin (Cu [86%] / Mn [12%] / Ni [2%] ).

History

In 1887, Edward Weston discovered that metals can have a negative temperature coefficient of resistance, inventing what he called his "Alloy No. 2." It was produced in Germany where it was renamed "Konstantan".

Constantan alloy

Of all alloys used in modern strain gauges, constantan is the oldest, and still the most widely used. This situation reflects the fact that constantan has the best overall combination of properties needed for many strain gauge applications. This alloy has, for example, an adequately high strain sensitivity, or gauge factor, which is relatively insensitive to strain level and temperature. Its resistivity () and this characteristic should be taken into account when zero stability of the strain gauge is critical over a period of hours or days. Constantan is also used for electrical resistance heating and thermocouples.

A-alloy

Very importantly, constantan can be processed for self-temperature compensation to match a wide range of test material coefficients of thermal expansion. A-alloy is supplied in self-temperature-compensation (S-T-C) numbers 00, 03, 05, 06, 09, 13, 15, 18, 30, 40, and 50, for use on test materials with corresponding thermal expansion coefficients, expressed in parts per million by length (or μm/m) per degrees Fahrenheit.

P alloy

For the measurement of very large strains, 5% (50,000 microstrain) or above, annealed constantan (P alloy) is the grid material normally selected. Constantan in this form is very ductile; and, in gauge lengths of 0.125 in and longer, can be strained to 20%. It should be borne in mind, however, that under high cyclic strains the P alloy will exhibit some permanent resistivity change with each cycle, and cause a corresponding zero shift in the strain gauge. Because of this characteristic and the tendency for premature grid failure with repeated straining, P alloy is not ordinarily recommended for cyclic strain applications. P alloy is available with S-T-C numbers of 08 and 40 for use on metals and plastics, respectively.

Physical properties

Property	Value
Electrical resistivity at room temperature
Temperature coefficient at	8 ppm·K−1
Temperature coefficient	±40 ppm·K−1
last1=Varanasi	first1=C. V.	last2=Brunke	first2=L.	last3=Burke	first3=J.	last4=Maartense	first4=I.	last5=Padmaja	first5=N.	last6=Efstathiadis	first6=H.	last7=Chaney	first7=A.	last8=Barnes	first8=P. N.	doi=10.1088/0953-2048/19/9/002	title=Biaxially textured constantan alloy (Cu 55 wt%, Ni 44 wt%, Mn 1 wt%) substrates for YBa2Cu3O7−x coated conductors	journal=Superconductor Science and Technology	volume=19	issue=9	pages=896	year=2006	bibcode=2006SuScT..19..896V	s2cid=119007573}}	35 K
Density	8.9 × 103 kg/m3
Melting point
Specific heat capacity	390 J/(kg·K)
Thermal conductivity at	19.5 W/(m·K)
Linear coefficient of thermal expansion at
Tensile strength
Elongation at fracture
Elastic modulus

Temperature measurement

Constantan is also used to form thermocouples with wires made of iron, copper, or chromel. It has an extraordinarily strong negative Seebeck coefficient above 0 degrees Celsius, leading to a good temperature sensitivity.

References

Bibliography

References

M. A. Laughton. (2003). "Electrical Engineers Reference Book". Elsevier.
J. R. Davis. (2001). "Copper and Copper Alloys". ASM International.
(1946). "A chronological history of electrical development from 600 B.C.". National Electrical Manufacturers Association.
D. O. Woodbury. (1949). "A measure for greatness: a short biography of Edward Weston". McGraw-Hill.
Hannah, R.L.. (1992). "Strain Gage Users' Handbook". Springer.
(2015-03-12). "Working with Chromel, Alumel & Constantan".
J. O'Malley. (1992). "Schaum's outline of theory and problems of basic circuit analysis". McGraw-Hill Professional.
(2006). "Biaxially textured constantan alloy (Cu 55 wt%, Ni 44 wt%, Mn 1 wt%) substrates for YBa2Cu3O7−x coated conductors". Superconductor Science and Technology.
Handbook of Temperature Measurement Vol. 3, edited by Robin E. Bentley

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