RTD (resistive temperature device) elements are wire windings or other thin-film serpentines that exhibit changes in resistance with changes in temperature. They are usually made of metallic elements or alloys such as copper, nickel, or nickel-iron. The most linear, repeatable devices are made of platinum, a precious metal that is suitable for temperature measurements over a wide operating range. RTD elements use two basic sensing technologies. Wire-wound devices consist of a coil of insulated wire wrapped around a ceramic or glass core. Thin-film devices also use ceramic substrates, but are smaller than traditional wire-wound devices. Multi-element products combine two or more RTD elements in a single sensor/transducer package to provide redundancy in case the primary element fails. RTD elements are often used with RTD probes and interfaced to RTD temperature transmitters, devices that convert resistance measurements to current signals.
