Constantan is a proprietary name for a copper– nickel

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...

also known as Eureka, Advance, and Ferry. It usually consists of 55% copper and 45% nickel. Its main feature is the low thermal variation of its

resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...

, which is constant over a wide range of temperatures. Other

alloys An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...

with similarly low temperature coefficients are known, such as

manganin Manganin is a trademarked name for an alloy of typically 84.2% copper, 12.1% manganese, and 3.7% nickel. It was first developed by Edward Weston in 1892, improving upon his Constantan (1887). Manganin foil and wire is used in the manufacture of ...

(Cu 6%/ Mn 2%/ Ni %).

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 modern strain gauge alloys, 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 Gauge factor (GF) or strain factor of a strain gauge is the ratio of relative change in electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , ...

, which is relatively insensitive to strain level and temperature. Its

(4.9 x 10⁻⁷ Ω·m) is high enough to achieve suitable resistance values in even very small grids, and its temperature coefficient of resistance is fairly low. In addition, constantan is characterized by good

fatigue life In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts of ...

and relatively high elongation capability. However, constantan tends to exhibit a continuous drift at temperatures above ; and this characteristic should be taken into account when

zero 0 (zero) is a number representing an empty quantity. In place-value notation such as the Hindu–Arabic numeral system, 0 also serves as a placeholder numerical digit, which works by multiplying digits to the left of 0 by the radix, usuall ...

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 In physics, deformation is the continuum mechanics transformation of a body from a ''reference'' configuration to a ''current'' configuration. A configuration is a set containing the positions of all particles of the body. A deformation can ...

) or above, annealed constantan (P alloy) is the grid material normally selected. Constantan in this form is very

ductile Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...

; and, in gauge lengths of 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

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

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typica ...

s and plastics, respectively.

Physical properties

Temperature measurement

Constantan is also used to form thermocouples with wires made of iron, copper, or

chromel Chromel is an alloy made of approximately 90% nickel and 10% chromium by weight that is used to make the positive conductors of ANSI Type E (chromel-constantan) and K (chromel- alumel) thermocouples. It can be used at temperatures up to in oxidizi ...

. It has an extraordinarily strong negative Seebeck coefficient above 0 degrees Celsius,Handbook of Temperature Measurement Vol. 3, edited by Robin E. Bentley leading to a good temperature sensitivity.

References

Bibliography

*{{ cite book , author = J. R. Davis , title = Copper and Copper Alloys , publisher = ASM International , year = 2001 , isbn = 0-87170-726-8

External links

National Pollutant Inventory - Copper and compounds fact sheet
Copper alloys Electric heating Nickel alloys