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