Thermocouple – is the most suitable method for measuring temperature and works as a temperature sensor: a temperature differential at each end of circuit formed by joined together two different kind of metal conductors produce a voltage. The resultant EMF will be proportional to the temperature difference between junctions. As a metal conductor usually it can be thermocouple wire of the following grades: NiCr, NiCrSi, NiSi/NiAl, CuNi, Fe, Cu, Pt, Rh.

According to the type of conductor the thermocouples are classified:

• NiCr-NiSi (Тype К);
• NiCr-CuNi (Тype E);
• Fe-CuNi (Тype J);
• Cu-CuNi (Тype T);
• NiCrSi-NiSi (Тype N);
• Pt10%Rh-Pt (Тype S);
• Pt13%Rh-Pt (Тype R);
• Pt30%Rh-Pt6%Rh (Тype B) etc.

Thermocouple types can be created with numerous combinations of alloys, the most commonly used are the types К, J, N, E and T.

Nickel alloys (Nickel 200 – 212) – nickel based alloys with Ni content 97-99% and impurities in a form of Mn, Mg, Cu, Si, Fe and other. Among advantages of nickel alloys the following can be noted:

• high electric conductivity;
• excellent corrosion resistance;
• high Curie temperature;
• high mechanical strength;
• high heat resistance;

Nickel-copper alloys are represented by series of Monel alloy (Alloy 400 – 500) primarily composed of nickel (up to 67%) and copper, with some iron and other trace elements. Monel has a good ductibility, a high resistance and an excellent resistance to corrosion in a wide variety of environments. Monel is widely used in chemical, oil & gas and medical industry, as well as in shipbuilding and aerospace industry.

Copper-nickel alloys are copper-based alloys containing nickel as the main alloying element with a small addition of other elements such as aluminum, manganese, iron, zinc, and others. As a result of mixing of copper and nickel, the final alloy has a high corrosion resistance, and the electrical resistance and strength increase. Copper-nickel alloys are well treated in hot and cold conditions.

By application the copper-nickel alloys can be divided in two groups:

• structural;
• electric.

Structural includes high-strength and corrosion-resistant alloys such as Melchior, Neusilber and Cunial. Electric alloys have high electrical resistance and emf. The most well-known representatives of this group are the Copel and Constantan alloys. Copper-nickel alloys are used in electrical engineering (electric apparatus, rheostats, resistors, thermocouples, etc.), in the manufacture of tableware, medical industry, shipbuilding, and others.