Resistance thermometer (RTD) - definition
Resistance thermometer (RTD) - definition
A resistance thermometer (Resistance Temperature Detector, RTD) is a precision temperature sensor whose operating principle is based on the phenomenon of change in the electrical resistance of a metal as a function of temperature. As the temperature increases, the resistance of the conductor increases in a predictable and measurable manner, allowing the temperature value to be accurately determined by measuring the electrical resistance of the sensing element.
The active element of a resistance thermometer is usually a thin wire or layer of metal with well-known temperature properties, most commonly platinum, due to its chemical stability, resistance to oxidation and the linear nature of resistance changes. Platinum sensors, such as PT100 or PT1000, denote 100 and 1000 ohms of resistance at 0 °C, respectively, and are commonly used in industrial, scientific and laboratory measurements.
RTDs are characterised by high accuracy, repeatability and long-term measurement stability. Their temperature response is well described by a non-linear function that can be converted to a linear approximation or described by the Callendar-Van Dusen equations. Others circuit configurations - two-, three- or four-wire - are used to measure resistance in RTD thermometers, aiming to eliminate errors due to the resistance of the connecting cables.
Resistance thermometers are used in industrial automation systems, process monitoring, HVAC systems, power generation, aerospace and medical and food applications. Their operation can be integrated with analogue and digital transmitters, enabling the processing of the resistance signal into voltage, current or digital signals according to the requirements of the control system and Data Acquisition Systems.
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