Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. A platinum resistance thermometer (PRT) is a device which determines the temperature by measuring the electrical resistance of a piece of pure platinum wire. The piece of platinum wire is referred to as a temperature sensor. Many RTD elements consist of a length of fine wire wrapped around a ceramic or glass core but other constructions are also used.

Platinum wire having resistance of 2.8 ohms wound on a mica frame. Two leads of Platinum wire and two compensatory leads terminals are provided. Enclosed in Pyrex Glass tube