Resistance Temperature Detectors (RTDs) are sensors that measure tem-perature by correlating the resistance of the RTD element with tempera-ture. Most RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core. The element is typically relatively fragile, so it is generally installed inside a sheath to protect it. The RTD element is con-structed from a pure material, the resistance of which, at various tempera-tures, has been documented by various international standards institutes. The material has a predictable change in resistance as the tem-perature varies; it is this change that is used to determine temperature.
RTDs are generally considered to be among the most accurate temperature sensors available. In addition to offering very good accuracy, they pro-vide excellent stability and repeatability. RTDs also feature high immunity to electrical noise and are, therefore, well suited for applications in process and industrial automation environments, especially around motors.