A temperature sensor which contains a resistor (typically 100 or 1000 Ohms). The resistance changes with temperature; this can then be correlated to provide a temperature reading. RTDs are considered to be amongst the most accurate temperature sensors available.
In addition to offering very good accuracy, they provide excellent stability, repeatability and have a high immunity to electrical noise. This means RTD Sensors are well suited for applications in process and industrial automation environments, especially around motors, generators and other high voltage equipment.