What type of temperature measuring device requires a reference temperature?

A thermocouple is a temperature measuring device that generates a voltage based on the temperature difference between two junctions made of different metals. One junction is placed in the environment whose temperature is being measured, while the other is kept at a known reference temperature, often referred to as the cold junction. The difference in temperature between these two junctions is what creates the voltage signal, which can be interpreted to determine the measured temperature.

This reliance on a reference temperature is crucial for accurately interpreting the generated voltage and translating it into a temperature reading. The other devices mentioned, such as thermistors, infrared sensors, and resistance temperature detectors (RTDs), operate differently. For instance, thermistors and RTDs measure temperature based on changes in resistance with temperature but do not require a separate reference temperature for their operation in the same way that thermocouples do. Infrared sensors measure temperature from the thermal radiation emitted by an object rather than needing a reference point.