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a cupronickel alloy characterized by low dependence of resistance on temperature. The constantan produced in the USSR contains 39–41 percent nickel, 1–2 percent manganese, and the balance copper. The specific resistance of constantan is about 0.48 microhm.m at 20°C, and the temperature coefficient of resistance after special heat treatment (stabilizing annealing) is about 2 × 10−6 1/0K; melting point, 1260°C.
Constantan is used in electrical engineering for the manufacture of rheostats and of elements in measuring devices. A short-coming of constantan is its high thermoelectromotive force (about 39 microvotts per degree Kelvin) in contact with copper. For this reason it is seldom used in high-precision instruments, since the random heating of any contact generates a current in the circuit that distorts the readings of the instrument. Manganin is usually used in the most critical cases. With copper or iron, constantan forms thermocouples that are suitable for measuring temperatures of up to 500°C.
L. L. ZHUKOV