Constantan® is a copper-nickel alloy that contains specific
minor amounts of additional elements to achieve precise
values for the temperature coefficient of resistivity. Careful
control of melting and conversion practices results in a very
low level of pinholes at ultra-thin thicknesses. The alloy is
used extensively for foil resistors and
strain gauges.
The TCR can be adjusted from the furnished cold rolled
values by using a low temperature heat treatment to
achieve compensation for all types of spring elements.
The foil is normally supplied with 90% cold reduction and
a smooth bright surface. The foil is reasonably flat at 4”
wide and nearly free of pinholes. The cold rolled foil can be
produced with a TCR between +10 to –35 PPM/°C. The
heat treatment will shift the foil TCR to the desired value.
A typical heat-treat curve for Constantan® shows
decreasing resistivity but increasing TCR with increased
heat-treating temperature.
Sizes
Constantan® is available from Hamilton Precision Metals
as foil and strip product in thicknesses from 0.0005” to
0.050” (0.0127 mm to 1.27 mm) and in widths up to
12” (304.8 mm). It is also available as thin as 0.000100”
(0.00254 mm) and in widths up to 4” (101.6 mm) maximum.
Nominal Composition
| NOMINAL COMPOSITION |
| Nickel |
44.2% |
| Manganese |
1.5% |
| Iron |
0.50 |
| Copper |
Balance |
Typical Mechanical Properties of Constantan® Alloy
|
ANNEALED |
COLD ROLLED |
| Ultimate Tensile Strength |
60,000 PSI. |
120,000 PSI |
| Elongation in 2” * |
25% |
2% |
| Modulus of Elasticity (Tension) |
24 x 106 PSI |
|
Physical Properties of Constantan® Alloy
| PHYSICAL PROPERTIES |
| Density |
0.321 lbs/cu.in |
| Melting Point (Approx.) |
1210°C |
| Electrical Resistivity @ R.T |
50.8 Microhm·cm |
| Temperature Coefficient of Resistivity (TCR) (25° to 105°C) |
± 30 PPM/°C |
| Thermal Expansion Coefficient (20°C to 100°C) |
14.9 x 10-6/°C |
| Thermal EMF vs. Copper (0°C to 100°C) |
-0.043 Millivolts/°C |
| Thermal Conductivity R.T. |
21.2W/m·K |
| Magnetic Attraction |
None |
| Specific Heat |
0.094 gram·cal./°C |