Constantan Nicr Alloy

6J22/6J23/Constantan Electric Resisitance Foil for Linear Strain Gauges

NiCr Alloy Description: 

Kanthal (Alloy 875/815), a family of iron-chromium-aluminium (FeCrAl) alloys used in a wide range of high-temperature applications.

Constantan [Cu55Ni45] has a low temperature coefficient of resistivity and as a copper alloy, is easily soldered. Other constant-resistance alloys include manganin [Cu86Mn12Ni2], Cupron [Cu53Ni44Mn3]and Evanohm.

The Evanohm family of nickel-chrome alloys [Ni72Cr20Mn4Al3Si1],[Ni73Cr20Cu2Al2Mn1Si], have high resistance, low temperature coefficient of resistance, low electromotive force (Galvani potential) when in contact with copper, high tensile strength, and also are very stable with regards to heat treatment.

Balco [Ni70Fe30] and similar alloys have very high, but more linear, temperature coefficient of resistivity, making them suitable for sensing elements.

Many elements and alloys have been used as resistance wire for special purposes. The table below lists the resistivity of some common materials. The resistivity of amorphous carbon actually has a range of 3.8 - 4.1 × 10−6 Ω m.

Typical Practice: 

For measurements of small strain, semiconductor strain gauges, so called piezoresistors, are often preferred over foil gauges. A semiconductor gauge usually has a larger gauge factor than a foil gauge. Semiconductor gauges tend to be more expensive, more sensitive to temperature changes, and are more fragile than foil gauges.

Nanoparticle-based strain gauges emerge as a new promising technology. These resistive sensors whose active area is made by an assembly of conductive nanoparticles, such as gold or carbon, combine a high gauge factor, a large deformation range and a small electrical consumption due to their high impedance.

In biological measurements, especially blood flow and tissue swelling, a variant called mercury-in-rubber strain gauge is used. This kind of strain gauge consists of a small amount of liquid mercury enclosed in a small rubber tube, which is applied around e.g., a toe or leg. Swelling of the body part results in stretching of the tube, making it both longer and thinner, which increases electrical resistance.

Fiber optic sensing can be employed to measure strain along an optical fiber. Measurements can be distributed along the fiber, or taken at predetermined points on the fiber. The 2010 America's Cup boats Alinghi 5 and USA-17 both employ embedded sensors of this type.
 

The following different kind of strain gauges are available in the market:

• Linear strain gauges
• Membrane Rosette strain gauges
• Double linear strain gauges
• Full bridge strain gauges
• Shear strain gauges
• Half bridge strain gauges
• Column strain gauges
• 45°-Rosette (3 measuring directions)
• 90°-Rosette (2 measuring directions).