Constantan
Template:Short description Template:Infobox material
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>Template:Cite book</ref> It usually consists of 55% copper and 45% nickel.<ref name=Davis158>Template:Cite book</ref> 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%] ).
HistoryEdit
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".<ref>Template:Cite book</ref><ref>Template:Cite book</ref>
Constantan alloyEdit
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 (Template:Val)<ref name=Davis158/> 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 a good fatigue life and relatively high elongation capability. However, constantan tends to exhibit a continuous drift at temperatures above Template:Convert;<ref>Template:Cite book</ref> 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.<ref name="keatsmfg.com">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
A-alloyEdit
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 alloyEdit
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 Template:Convert 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 propertiesEdit
| Property | Value |
|---|---|
| Electrical resistivity at room temperature<ref name=Davis158/> | Template:Val |
| Temperature coefficient at Template:Val<ref>Template:Cite book</ref> | 8 ppm·K−1 |
| Temperature coefficient Template:Val<ref name=Davis158/> | ±40 ppm·K−1 |
| Curie point<ref name=Varanasi>Template:Cite journal</ref> | 35 K |
| Density<ref name=Davis158/> | 8.9 × 103 kg/m3 |
| Melting point | Template:Val |
| Specific heat capacity | 390 J/(kg·K) |
| Thermal conductivity at Template:Val | 19.5 W/(m·K) |
| Linear coefficient of thermal expansion at Template:Val<ref name=Davis158/> | Template:Val |
| Tensile strength<ref name=Davis158/> | Template:Val |
| Elongation at fracture | <45% |
| Elastic modulus | Template:Val |
Temperature measurementEdit
Constantan is also used to form thermocouples 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.
ReferencesEdit
BibliographyEdit
External linksEdit
- National Pollutant Inventory - Copper and compounds fact sheet (archived 2008)