The operating principle, operating equations, fabrication, calibration recomendations and specifications are given for platinum RTDs. International industrial RTD standards exist only for platinum RTDs. Platinum RTDs are more efficient to produce, cover the widest temperature range by 2x or more and overwhelmingly outperform obsolete base-metal RTDs.
100 Ω platinum RTD 3-wire connections common in industry normally provide adequate cancelation of lead resistance up to tens of feet. 1000 ohm platinum thin film RTDs provide comparable performance with 2-wire connections because series lead resisitance offsets are 10x smaller.
A major advantage of platinum RTDs is that calibration at as few as two temperatures offers accuracy, preserved by high stability, much tighter than defined classes of interchangeability. No other temperature sensor offers specifications for stability that will preserve laboratory accuracies embedded in calibrations over long periods and wide temperature ranges in every configuration.
Doris Garvey is a product engineer at
©RdF Corporation, 2003,
Expanded and retitled.
Originally published as “So, What is an RTD?”
SENSORS, Aug. 1999, AN ADVANSTAR PUBLICATION