Post by JG
The most popular RTD is PT-100, Platinum 100 Ohms, As all Metals have a Temperature Coefficient of Resistance. The Resistance of RTD increases with rise in temperature.
Even Copper wire can be used, but you need to have a very thin and long wire to make usable measurements.
Resistance: Temperature Coefficient - Since the electrical resistance of a conductor such as a copper wire is dependent upon collisional proccesses within the wire, the resistance could be expected to increase with temperature since there will be more collisions
Resistance thermometer - Wikipedia - . The RTD wire is a pure material, typically platinum, nickel, or copper. The material has an accurate resistance/temperature relationship which is used to provide an indication of temperature. As RTD elements are fragile, they are often housed in protective probes.
What are RTDs? - in the case of Platinum known variously as PRTs and PRT100s, are the most popular RTD type, nearly linear over a wide range of temperatures
What is a Resistance Temperature Detector (RTD)? - Most RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core.
The material has a predictable change in resistance as the temperature changes; it is this predictable change that is used to determine temperature.
This is an answer of mine to an old post - 2006