resistance thermometer

Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors that use the electrical resistance of a substance (such as platinum) to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a heat-resistant ceramic or glass core but other constructions are also used. The RTD wire is typically platinum (Pt), nickel (Ni), or copper (Cu). The material has an accurate temperature–resistance relationship which is used to provide an indication of temperature. Ruthenium oxide is commonly used to make RTDs that operate at cryogenic temperatures. As RTD elements are fragile, they are often housed in protective probes called thermowells. RTDs have higher accuracy and repeatability than thermocouples, which is why they are slowly replacing them in industrial applications below 600 °C.

Resistance/temperature relationship of metals