What is an RTD? How does it work?

Instrumentation Temperature
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What is an RTD?

RTD – Resistance Temperature Detector

RTD is a positive temperature coefficient resistance which provides a linear rise in its resistance versus the rise in temperature.

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Resistance thermometer use metals that alter their electric resistance when heated.

Platinum is most commonly used material for industrial RTD. However copper and Nickel are also used for some applications. The resistance at 0ºC is called R and it is important parameter to be defined.

The most commonly used RTD element is of Platinum with resistance of 100O at 0ºC. RTD has a positive temperature coefficient. Normally industrial RTD are used up to temperature range of 400ºC.

Working:

  • In RTD, The change in resistance value is very small with respect to the temperature. So, the bridged circuit is used.
  • Constant electric current is supplied to bridged circuit and voltage drop is measured across the resistor, through which resistance is measured. Thereby, the temperature can also be determined.
  • This temperature is determined by converting the RTD resistance value using a calibration expression.