RTD Temperature to Resistance calculation formula with Example

RTD

RTD (Resistance Temperature Detector) is a sensor whose resistance changes as its temperature changes. The resistance increases as the temperature of the sensor increases. The resistance vs temperature relationship is well known and is repeatable over time. An RTD is a passive device. It does not produce an output on its own. External electronic devices are used to measure the resistance of the sensor by passing a small electrical current through the sensor to generate a voltage

Resistive Temperature Detectors (RTDs) relate resistance to temperature by the following formula:

   RT = Rref[1 + α(T − Tref)]

Where,

RT = Resistance of RTD at given temperature T (ohms)
Rref = Resistance of RTD at the reference temperature Tref (ohms)
α = Temperature coefficient of resistance (ohms per ohm/degree)

Example:

The following example shows how to use this formula to calculate the resistance of a PT100 RTD with a temperature coefficient value of 0.00392 at a temperature of 35 degrees Celsius:

Assuming Temperature Reference = 0 Degrees

For PT100 RTD the Rref = 100

RT = 100 Ω[1 + (0.00392)(35 − 0)]

RT = 100 Ω[1 + 0.1372]

RT = 100 Ω[1.1372]

RT = 113.72 Ω

For Temperature to Resistance conversion also the same above formula applies.

The above given is a basic equation only for RTD calculation.

Note:

1.The above RTD calculation tool designed for a standard PT100 sensor.