Thin-film RTD elements are made by depositing a very thin layer of metal (usually platinum) onto a ceramic substrate material. They also tend to be more vibration sensitive. However, they are more expensive to manufacture than thin-film types, requiring skilled labor and advanced assembly facilities. Those with glass cores can readily be immersed in many liquids, while those with ceramic cores can be used to accurately measure extremely high temperatures. Wire-wound RTDs (especially the inner-coil type) are the most accurate type of RTD. They can also be fitted into custom housings. This protects them from their surroundings and increases their durability. Wire-wound RTD sensing elements can easily be made into Pt100 probes by mounting them inside metal tubes or sheaths. This wire coil can be packaged inside a ceramic or glass tube (the most common construction) or the wire can be wound around the outside of a ceramic or glass housing material. In the wire-wound type of RTD, the sensing element is comprised of a small coil of ultra-thin wire (typically platinum). Each type is best suited for use in certain environments and applications. One type of RTD contains wire-wound elements and the other type of RTD contains thin-film elements. RTDs available today can generally be categorized into one of two basic types, depending on how their temperature sensing element is constructed.

Siemens, soon discovered that a platinum element yielded more accurate readings at a much wider range of temperatures. The first-ever resistance thermometer was assembled from insulated copper wire, a battery, and a galvanometer in 1860. The invention of a resistance thermometer was made possible by the discovery that the conductivity of metals decreases predictably with increases in their temperatures. Generally, a bare resistance element is too fragile and sensitive to be used in its raw form, so it must be protected by incorporating it into an RTD (Pt100 or Pt1000). These resistance elements are the heart of Resistance Temperature Detectors (RTDs). In this way, by measuring the resistance of the element, the temperature of the element can be determined from tables, calculations, or instrumentation. But they all function in the same manner: each has a pre-specified resistance value at a known temperature which changes in a predictable fashion. Resistance elements come in many types conforming to different standards, capable of different temperature ranges, with various sizes and accuracies available.

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