Skip to content NREL Buildings Research National Renewable Energy Laboratory (NREL)
Field Test Best Practices: A Resource for Practical Residential Building Science

Main menu

Resistance Temperature Detectors (RTD)

Resistance Temperature Detectors, or RTDs, are an alternative to a thermocouple where accuracy and repeatability are of highest importance. An RTD is a resistor whose resistance varies directly and linearly with temperature. It is more expensive and has a slower response than a thermocouple, so is not as appropriate for general temperature measurements. Data logger capabilities and requirements should be considered when planning to use an RTD in a field test.

Typically a current is applied to an RTD, and the voltage drop measured (or vice versa) to calculate resistance. Care must be taken to keep the current below manufacturer stated limits, to prevent RTD self-heating.

Most RTDs measure at 100Ω at 0°C, with a measurement slope of 0.00392/°C. RTDs are very stable over time. Check the calibration sheet with your RTD to ensure the measurement is converted correctly. The signal wiring has a resistance as well, so it should be carefully chosen and measured at installation to ensure that resistance does not skew your measurements. Due to this, 2-wire RTDs are less accurate than 3- and 4-wire RTDs.