Constantan

Constantan is the oldest among all modern strain gauge alloys which 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 an adequately high strain sensitivity, or gauge factor, which is relatively insensitive to strain level and temperature. Resistivity of Constantan is high enough to achieve suitable resistance values in even very small grids, and its temperature coefficient of resistance is not excessive. Constantan is outstanding with its perfect fatigue life and relatively high elongation capability. It must be noted, however, that Constantan tends to exhibit a continuous drift at temperatures above 65 °C (150 °F); and this characteristic should be taken into account when zero stability of the strain gauge is critical over a period of hours or days. Moreover, Constantan is very popular alloy which has such a peculiarity as resistivity (constantan doesn’t change its resistance features at high temperatures).

Constantan - silver-yellow alloy that contains 58-60% Cu, 32-40% Ni and 1-2% Mn. temperature of melting of constantan 1260°С. the density of the 8900 kg/m3, TKR = 14 * 10-6 1/OC.

Advantage

Electrical Constantan resistivity almost does not depend on temperature. Specific electrical resistance of Constantan 0,48мком×m is at 20 C. After a special stabilizing heat treatment (annealing) temperature coefficient of electrical resistance of Constantan reaches 2×10-6 1/K and the electrical resistivity not depend on the temperature. A soft (annealed) of Constantan - sp = 400...500 Mpa, the ep = 40...50%, r = 0, 45...0, 48 Ohm * mm2/m, while the solid - sp = 650...720 Mpa, the ep = 2...5%, r = 0.46 a...0, 52 Ohm * mm2/m.

Disadvantages

Substantial lack of constantan – is large thermoemf (40-50?V/C) in pair with copper, which limits its use in stable resistors and high-precision instruments  as heating terminals leads to the appearance of current, distorting evidence. Therefore, if you need high accuracy – apply Manganin.

Application

Strip are manufactured of constantan wire is 0.03-5 mm and with thickness of up to 0.1 mm. Large thermoemf of constantan in pair with copper has determined its application in thermocouples for accurate measurements at relatively low operating temperatures (up to 500 C). It is usually used in thermocouples where positive thermo electrode is Iron, Copper and Chrome, and the negative - Constantan, Alumel and Copel. Wide application of constantan found also in the manufacture of compensation wires, rheostats, heating devices.

As for Constantan wire, it is used for special heating purposes (electric kettles, heating elements etc.) Constantan wire resistivity – it is 44% of nickel and 56% of copper. It is necessary that Constantan wire resistance, as other metal wires, must be insulated at high red hot temperatures. Unfortunately most sheaths are not useful in this case.

Delivery

As Constantan is most often used in pyrometry the main type is constantan-wire. The price of constantan is dictated by the value of Copper and Nickel, which are the basis of Constantan.

The alloy is supplied in the following forms:

• Constantan - strip (thickness of 0.1-5 mm, width 3-600mm).

• Constantan - rod (12 mm - 100 mm in diameter);

• Constantan - wire (0,1 - 12 mm in diameter);