resistance temperature detector (RTD)
Resistance Temperature Detectors(RTD) are thermistors consisting of a platinum wire or a platinum layer vapor deposited on an oxide platelet using thin-film technology and exploit the positive temperature coefficient of metals, which becomes apparent through higher resistance as the temperature rises. The higher the temperature, the higher the electrical resistance.
RTD elements are used, among other things, as temperature-dependent resistance thermometers, or bolometers. They use platinum (Pt), which is characterized by a particularly high linearity of the resistance value. The measuring accuracy of these temperature sensors is in the range of +/-0.1°C. To ensure that these elements have response times of fractions of a second, the platinum elements are extremely small and have a low heat capacity. In the case of sensors, the RTD elements are housed in encapsulated probes. In addition to platinum, other metals used include copper, nickel, and iron-nickel and other alloys.
To minimize measurement errors due to lead wires, special circuits with three or four lead wires in a bridge configuration are used. These are often Wheatstone bridges.
The temperature range for RTD elements is between -260°C and +1,000°C. RTD thermocouples are commercially available for resistance ranges between 10 ohms and 25 kilo-ohms. Commonly used RTD elements are 100-ohm, 200-ohm, and 1-kilo-ohm strainless platinum. In general, it can be stated that the higher the resistance, the lower the influence of the connecting wires and the circuits.
One of the best known platinum sensors is the Pt100, which got its name from its resistance value of 100 ohms at 0°C.