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RTDs vs. Thermocouples A Comparison of Properties and Costs


 A Resistance Temperature Detector, or RTD, measures temperature by measuring the electrical resistance of a metallic sensing element. Electrical resistance rises as the element becomes hotter with increasing heat. Electrical resistance falls as the element becomes cooler with decreasing heat.

An RTD measures the change in local temperature by detecting the change in the electrical resistance of specific metals. An RTD sensor element is either a finely coiled platinum, nickel, or copper wire wound around a ceramic core or a thin film of platinum, nickel, or copper wire encapsulated in an element substrate. To protect the element, it is usually installed in a sheath.

RTD sensor elements are constructed from pure materials that have their resistance at various temperatures well documented. As the temperature changes, the material’s resistance changes in a predictable and calculable way, which is used to determine the temperature. An example of the Platinum Resistance vs. Temperature curve can be seen in Figure 1. In addition to providing high accuracy, RTD’s offer excellent short- and long-term stability and repeatability.

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