Resistance temperature detectors (RTDs) are temperature sensors whose resistance varies with temperature. Platinum is the most common, most accurate, wire material. Nickel, copper, and other metals may also be used to make RTDs. Characteristics include a wide temperature range (up to +850°C), excellent accuracy and repeatability, reasonable linearity, and the necessity for signal conditioning. Because of their accuracy, stability, and wide temperature range, RTDs are used in a variety of precision applications, including instruments, process control, and automotive systems. For Pt-RTDs, the most common values for nominal resistance at 0°C are 100 Ω and 1 kΩ, though other values are available. The number of wires connected to the two nodes of the RTD varies depending upon the application. Because RTDs are resistive elements, resistance in connecting cables can introduce errors in the measurement. To address this, RTDs that will be used longer distances from the signal conditioning circuitry are available in three or four wire configurations, while a simple two wire RTD is sufficient for short distances.