Additional Information
An RTD, or Resistance Temperature Detector, is a temperature sensing device with resistance that increases with temperature. An RTD is usually constructed with wire coil or deposited film of pure metal. RTDs can be made of different metals and have different nominal resistances, but the most popular RTD is platinum and has a nominal resistance of 100 Ω at 0 °C.
Numerous types of RTDs exist, and they are typically defined by their material, their nominal resistance, and their temperature coefficient of resistance (TCR). The TCR, or α, of an RTD is the average temperature coefficient of resistance of the RTD from 0 to 100 °C and is the most common method of specifying the behavior of an RTD. The TCR for platinum RTDs is determined by the Callendar-Van Dusen equation.
The Callendar-Van Dusen equation is as follows:
Temperatures below 0 °C:
RT = R0[1 + A × T + B × T2 + C × T3 × (T – 100 °C)]
Temperatures above 0 °C:
RT = R0[1 + A × T + B × T2]
T = temperature in degrees Celsius
RT = RTD resistance at temperature T
R0 = RTD nominal resistance at 0 °C
A, B, and C = coefficients are listed in the help document: Platinum RTD Types.