Resistance Temperature Detectors (RTD sensors) are temperature sensors that contain a resistor that changes resistance value as its temperature changes. Resistance Temperature Detectors, as the name implies, are sensors used to measure temperature by correlating the resistance of the RTD element with temperature. RTD Sensors are also called as Resistance Thermometers, Resistive Thermal Devices. As they are almost invariably made of platinum, they are often called Platinum Resistance Thermometers (PRT). They are slowly replacing the use of thermocouples in many industrial applications below 600 °C, due to higher accuracy and repeatability. RTD sensors have been used for many years to measure temperature in laboratory and industrial processes, and have developed a reputation for accuracy, repeatability, and stability. Wireless RTD sensor transmitters transmit the real-time temperature data to industrial computer system.

RTD Sensors Vs Thermistors & Thermocouples

Why use an RTD Sensor instead of a thermocouple or thermistor sensor? Each type of temperature sensor has a particular set of conditions for which it is best suited. In comparison of RTD Sensor Vs Thermistor & Thermocouple, RTD sensors offer several advantages:

  • A wide temperature range (-50 to 500°C for thin-film and -200 to 850°C for wire-wound)
  • Good accuracy (better than thermocouples)
  • Good interchangeability
  • Long-term stability
  • With a temperature range up to 850°C, RTDs can be used in all but the highest-temperature industrial processes.
  • RTD sensors are made using metals such as platinum, they are very stable and are not affected by corrosion or oxidation.
  • RTD sensors in industrial applications are rarely used above 660 °C. At temperatures above 660 °C it becomes increasingly difficult to prevent the platinum from becoming contaminated by impurities from the metal sheath of the thermometer. This is why laboratory standard thermometers replace the metal sheath with a glass construction. At very low temperatures, say below -270 °C (or 3 K), due to the fact that there are very few phonons, the resistance of an RTD is mainly determined by impurities and boundary scattering and thus basically independent of temperature. As a result, the sensitivity of the RTD is essentially zero and therefore not useful.
  • Compared to thermistors, platinum RTDs are less sensitive to small temperature changes and have a slower response time. However, thermistors have a smaller temperature range and stability.

Resistance thermometer RTD sensor elements are available in a number of forms. The most common are: unsupported wirewound RTD element, wirewound element in a ceramic insulator, wire encapsulated in glass, Thin-film platinum-film ceramic substrate RTD element.