Editing Constantan

{{Short description|Alloy of copper and nickel}}
{{Infobox material
| name = Constantan
| image = Konstantandraht.jpg
| image_size = 
| alt = 
| caption = A spool of Constantan wire
| type = Copper-nickel alloy
| density = {{convert|8885|kg/m3|g/cm3|disp=out}}
| youngs_modulus = 162 GPa
| tensile_strength = ~450 MPa
| elongation = ~0.25%
| melting_point = {{val|1210|u=degC}}
| thermal_conductivity kg·K)
| dielectric_constant_note = 
| dielectric_constant = 
| permittivity = 
| relative_permeability_note = 
| relative_permeability = 
| permeability_note = 
| permeability = 
| surface_resistivity = 0.56 μΩ·m
| volume_resistivity = 
}}

'''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.<ref>{{cite book |url=https://books.google.com/books?id=5jOblzV5eZ8C&pg=SA10-PA43 |title=Electrical Engineers Reference Book |edition=16th |year=2003 |author=M. A. Laughton |author2=D. F. Warne |publisher=Elsevier |isbn=0-7506-4637-3 |page=10/43}}</ref> It usually consists of 55%&nbsp;copper and 45%&nbsp;nickel.<ref name=Davis158>{{cite book |author=J. R. Davis |title=Copper and Copper Alloys |publisher=ASM International |year=2001 |isbn=0-87170-726-8 |page=158}}</ref> Its main feature is the low thermal variation of its [[resistivity]], which is constant over a wide range of temperatures. Other [[alloy]]s with similarly low [[temperature coefficient]]s are known, such as [[manganin]] (Cu [86%] / Mn [12%] / Ni [2%] ).

==History==
In 1887, [[Edward Weston (chemist)|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".<ref>{{cite book |url=https://books.google.com/books?id=6iRCAAAAIAAJ&q=constantan |title=A chronological history of electrical development from 600 B.C. |page=59 |publisher=National Electrical Manufacturers Association |year=1946}}</ref><ref>{{cite book |author=D. O. Woodbury |url=https://books.google.com/books?id=OiNVAAAAMAAJ&q=constantan |title=A measure for greatness: a short biography of Edward Weston |page=168 |publisher=McGraw-Hill |year=1949}}</ref>

==Constantan alloy==
Of all alloys used in modern [[strain gauge]]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 (materials science)|strain]] sensitivity, or [[gauge factor]], which is relatively insensitive to strain level and [[temperature]]. Its [[resistivity]] ({{val|5.00|e=−7|u=Ω·m}})<ref name=Davis158/> is high enough to achieve suitable resistance values in even very small grids, and its [[temperature coefficient]] of [[electrical resistance|resistance]] is fairly low. In addition, constantan is characterized by a good [[Fatigue (material)|fatigue life]] and relatively high [[elongation (materials science)|elongation]] capability. However, constantan tends to exhibit a continuous drift at temperatures above {{convert|65|C|F}};<ref>{{cite book |title=Strain Gage Users' Handbook |last=Hannah |first=R.L. |publisher=Springer |year=1992 |isbn=978-0412537202 |location=New York |page=50}}</ref> and this characteristic should be taken into account when [[0 (number)|zero]] stability of the strain gauge is critical over a period of hours or days. Constantan is also used for electrical resistance heating and [[thermocouple]]s.<ref name="keatsmfg.com">{{cite web |url=https://www.keatsmfg.com/blog/working-with-chromel-alumel-constantan/ |title=Working with Chromel, Alumel & Constantan |date=2015-03-12 |website=Keats Manufacturing Co. |language=en-US |access-date=2016-05-18}}</ref>

==A-alloy==
Very importantly, constantan can be processed for self-temperature compensation to match a wide range of test material [[coefficient of thermal expansion|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 [[ductility|ductile]]; and, in gauge lengths of {{convert|0.125|in|mm}} 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 [[0 (number)|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 [[metal]]s and [[plastic]]s, respectively.

==Physical properties==
{| class="wikitable
! Property
! Value
|-
|[[Resistivity|Electrical resistivity at room temperature]]<ref name=Davis158/>||{{val|5.00|e=−7|u=Ω·m}}
|-
|[[Temperature coefficient]] at {{val|20|u=degC}}<ref>{{cite book |author=J. O'Malley |title=Schaum's outline of theory and problems of basic circuit analysis |page=[https://archive.org/details/schaumsoutlineof00omal/page/19 19] |publisher=McGraw-Hill Professional |year=1992 |isbn=0-07-047824-4 |url-access=registration |url=https://archive.org/details/schaumsoutlineof00omal/page/19}}</ref> || 8 ppm·K<sup>−1</sup>
|-
|Temperature coefficient {{val|-55|to|105|u=degC}}<ref name=Davis158/> || ±40 ppm·K<sup>−1</sup>
|-
|[[Curie point]]<ref name=Varanasi>{{cite journal |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}}</ref> || 35 K
|-
|[[Density]]<ref name=Davis158/> || 8.9 × 10<sup>3</sup> kg/m<sup>3</sup>
|-
|[[Melting point]] || {{val|1221|-|1300|u=degC}}
|-
|[[Specific heat capacity]] || 390 J/(kg·K)
|-
|[[Thermal conductivity]] at {{val|23|u=degC}}|| 19.5 W/(m·K)
|-
|Linear [[coefficient of thermal expansion]] at {{val|25|to|105|u=degC}}<ref name=Davis158/>|| {{val|14.9|e=-6|u=K<sup>−1</sup>}}
|-
|[[Tensile strength]]<ref name=Davis158/> || {{val|455|-|860|u=MPa}}
|-
|[[Fracture|Elongation at fracture]] || <45%
|-
|[[Elastic modulus]] || {{val|162|u=GPa}}
|}

==Temperature measurement==
Constantan is also used to form [[thermocouple]]s with wires made of [[iron]], copper, or [[chromel]].<ref name="keatsmfg.com"/> It has an extraordinarily strong negative [[Seebeck coefficient]] above 0 degrees Celsius,<ref>Handbook of Temperature Measurement Vol. 3, edited by Robin E. Bentley</ref> leading to a good temperature sensitivity.

==References==
{{Reflist}}

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

==External links==
*[https://web.archive.org/web/20080302034606/http://www.npi.gov.au/database/substance-info/profiles/27.html National Pollutant Inventory - Copper and compounds fact sheet] (archived 2008)

[[Category:Copper alloys]]
[[Category:Electric heating]]
[[Category:Nickel alloys]]