constantan

Constantan is a copper-nickel alloy, typically about 55% copper and 45% nickel. It is valued for its relatively high resistivity among copper alloys and, most importantly, for an unusually low temperature coefficient of resistance, making its electrical resistance change only slightly with temperature. The alloy is often prepared as wire, foil, or ribbon for industrial use.

Key properties include a resistivity of roughly 49 micro-ohm-centimeters at 20°C and a temperature coefficient on the order of a few tens of parts per million per degree Celsius (often cited as around −25 ppm/°C in practice). This combination of higher resistivity and low, stable temperature sensitivity, along with good ductility and corrosion resistance, makes constantan suitable for precision electrical applications. It can be readily drawn into thin wires and formed into resistive elements, with annealing used to adjust its mechanical state.

Common manufacturing uses include resistance-based components and sensors. Constantan wires are used in thermocouples as the reference leg in Type T thermocouples (copper-constantan) and as stable filler or compensation elements in some temperature measurement setups. It is also employed in resistive elements for heaters, precision resistors, and in strain-gauge applications where a stable resistance under temperature variation is desirable.

In summary, constantan’s combination of moderate resistivity, low and predictable temperature dependence, and good mechanical properties underpins its role in electrical instrumentation, especially for sensors and precision resistors.