RTD Types and Equation

RTD Types

  • Film thermometers-It is a thin layer of platinum (as thin as 1 µm). Advantages of this type of RTD are relatively low cost and fast response. Such devices have improved in performance although the different expansion rates of the substrate and platinum give “strain gauge” effects and stability problems.


  • Wire-wound thermometers– this type of thermometer have greater accuracy, especially for wide temperature ranges. The coil diameter provides a compromise between mechanical stability and allowing expansion of the wire to minimize strain and consequential drift


The relationship between temperature and resistance of conductors can be calculated from the equation.

R=Ro (1+α T)


R         = The resistance of the conductor at temperature t (°C)

Ro           = The resistance at the reference temperature, usually 20°C

α             = The temperature coefficient of resistance

T          = The difference between the operating and the reference