Resistance Temperature Detector

A resistance temperature detectors, abbreviated as RTD, are sensors used to measure temperature by correlating the resistance of the element with temperature.  Each RTD has a pre-specified resistance value at a known temperature which changes in a predictable fashion.  By measuring the resistance of the element, the temperature of that element can be determined from tables, calculations or instrumentation.

Most RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core.  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.  The element is usually quite fragile, so it is often placed inside a sheathed probe to protect it.