Figure 2 Internal Construction of a Typical RTD

Temperature Detectors RESISTANCE TEMPERATURE DETECTORS (RTDs) RTD elements are usually long, spring-like wires surrounded by an insulator and enclosed in a sheath of metal. Figure 2 shows the internal construction of an RTD. Figure 2 Internal Construction of a Typical RTD This particular design has a platinum element that is surrounded by a porcelain insulator. The insulator prevents a short circuit between the wire and the metal sheath. Inconel, a nickel-iron-chromium alloy, is normally used in manufacturing the RTD sheath because of its inherent corrosion resistance. When placed in a liquid or gas medium, the Inconel sheath quickly reaches the temperature of the medium. The change in temperature will cause the platinum wire to heat or cool, resulting in a proportional change in resistance. This change in resistance is then measured by a precision resistance measuring device that is calibrated to give the proper temperature reading. This device is normally a bridge circuit, which will be covered in detail later in this text. Rev. 0 Page 3 IC-01