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Facts at your Fingertips: Temperature Measurement with RTDs

By Scott Jenkins |

Temperature measurement is critical in many types of process equipment, including reactors, distillation columns, furnaces, heat exchangers, evaporators, boilers and more. Among the most widely used instruments for measuring temperatures in chemical process industries (CPI) operations are resistance temperature detectors (RTDs). This one-page reference describes the principles behind the operation of RTDs, and their advantages and limitations. RTD operation RTDs are temperature sensors that operate on the principle that a material’s electrical resistance changes with temperature in a predictable way. When an RTD is supplied with a constant current, the resulting voltage drop can be measured and the resistance calculated. The highly predictable relationship between RTD resistance and surrounding temperature allows the temperature to be determined accurately and reproducibly. RTDs can be connected in a two-, three-, or four-wire configuration, in which current is conducted through the RTD and the resulting voltage measured. The two-wire configuration is the simplest, but also the most prone to error, because the two connecting lead wires add some resistance to the RTD (Figure 1). This introduces error. The three-wire setup is similar,…
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