What does RTD stand for in temperature measurement?

• A. Resistive Temperature Detector - an electric thermometer that changes its resistance with temperature.
• B. A thermometer using infrared radiation to measure surface temperature.
• C. A device that measures pressure through a fluid column.
• D. A sensor that records humidity.

Answer: (A)

RTD stands for Resistive Temperature Detector, a type of electric thermometer that relies on a metal’s resistance changing with temperature. The sensing element—often platinum—exhibits a predictable increase in resistance as temperature rises. By measuring this resistance with a bridge or ohmmeter and applying a calibration, you convert the resistance reading directly to temperature (the resistance-temperature relationship is typically expressed as R = R0[1 + αΔT]). RTDs provide good accuracy, repeatability, and stability across a broad temperature range, which is why they’re widely used in industrial temperature measurements. Infrared-based devices measure surface temperature from emitted radiation, while other options describe pressure measurement with a fluid column or humidity sensing—different sensing principles that don’t rely on resistance changing with temperature.