Resistance thermometers are thermal control devices with good linearity, possibility of use in a wide range of temperature, although less than the use of thermocouples (maximum temperatures ≤900°C). The only drawback is their low sensitivity.
A theoretical outline
The metal thermoresistors (also called resistance thermometers), more commonly known as RTDs are based on change in electrical resistance of a metal as a function of temperature at which the same is subjected.
Among the most widely used materials for the construction of RTDs are mainly platinum and nickel, due to their high resistivity and stability.
The temperature measurements made by means of resistance thermometers are, in fact, significantly more accurate and reliable than those of the thermocouples.
Normally, the metal resistance thermometers are identified by the initials of the material used for their construction, or Platinum = Pt, Ni = Nickel, etc. …), followed by their nominal resistance at 0°C.
The field of industrial use of resistance thermometers is between -200 and +850 ° C as shown in the table.
The RTD is mainly divided into two subcategories: