Constantan, also known in various contexts as Eureka, Advance, and Ferry, refers to a copper-nickel alloy commonly used for its stable electrical resistance across a wide range of temperatures. It usually consists of 55% copper and 45% nickel. Its main feature is the low thermal variation of its

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

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

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

s with similarly low

temperature coefficient A temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature. For a property ''R'' that changes when the temperature changes by ''dT'', the temperature coefficient α is def ...

s are known, such as manganin (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 Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

where it was renamed "Konstantan".

Constantan alloy

Of all alloys used in modern

strain gauge A strain gauge (also spelled strain gage) is a device used to measure Deformation (mechanics)#Strain, strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an Electrical in ...

s, 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 Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

. Its

() is high enough to achieve suitable resistance values in even very small grids, and its

of resistance is fairly low. In addition, constantan is characterized by a good fatigue life 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. Adding (or subtracting) 0 to any number leaves that number unchanged; in mathematical terminology, 0 is the additive identity of the integers, rational numbers, real numbers, and compl ...

stability of the strain gauge is critical over a period of hours or days. Constantan is also used for electrical resistance heating and

thermocouple A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the ...

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 Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determining how large or small a physical quantity is as compared to ...

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 Ductility refers to the ability of a material to sustain significant plastic deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic deformation, which is reversi ...

; 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 () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

s and

plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...

s, respectively.

Physical properties

Temperature measurement

Constantan is also used to form

s with wires made of

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

, copper, or chromel. 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
(archived 2008) Copper alloys Electric heating Nickel alloys