Pt100 sensors are the most common type of platinum resistance thermometer. Often resistance thermometers are generally called Pt100 sensors, even though in reality they may not be the Pt100 type. Pt refers to that the sensor is made from Platinum (Pt). 100 refers to that at 0°C sensor has a resistance of 100 ohms (Ω).
See definition: Resistance thermometer
View Detailed Technical Information: Resistance Thermometer
View sensor designs: Pt100 sensors